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Abstract:

Abstract:Phosphorus is an essential element for plants, animals, and other living organisms. The lack of phosphorus in aquatic environments can restrict primary productivity, a concern that has increasingly attracted global attention. However, the high phosphorus concentration leads to the eutrophication of water bodies, impacting human activities, compromising water quality, and causing notable economic losses. Therefore, studies on phosphorus removal and the recovery of phosphorus resources are important. In 2023, 27.3% of China’s important fishery waters in inland rivers exceeded the total phosphorus standard. The area of marine natural important fishery waters that exceeded the standard for reactive phosphate was 27.0%, and the area of seawater key aquaculture areas that exceeded the standard for reactive phosphate was 28.2%,. Aquaculture development is particularly important in the context of the ‘Big Food Concept’. The China’s total aquatic product output in 2023 was 71.16 million tons, an increase of 4.39% year-on-year, of which aquaculture production accounted for 81.6%. From 2022 to 2024, China’s provinces and municipalities introduced the aquaculture tail water discharge standard. For example, Shandong Province has implemented DB37 4676-2023, which sets a total phosphorus primary discharge limit of 0.7 mg/L and a secondary discharge limit of 1.0 mg/L. Recently, the rapid development of aquaculture tailwater phosphorus removal technology and phosphorus recovery technology based on physical, chemical, biological and ecological methods has provided strong support for aquaculture tailwater phosphorus removal and recycling. The current aquaculture tailwater phosphorus removal technology has made some progress. However, the advanced removal of phosphorus from the tailwater and phosphorus recovery technology requires further investigation. Enhancing the advanced removal of aquaculture tailwater is essential to ensure the sustainable development of aquaculture. This study classified the phosphorus in the water, examined the principle and current status of aquaculture tailwater phosphorus removal technology, and reviewed the application of phosphorus removal in the tailwater of the current aquaculture model. The principles and current status of phosphorus removal technology in aquaculture tailwater were discussed in terms of physical, chemical, and biological methods of phosphorus removal. The study indicated that the physical method of phosphorus removal technology in aquaculture primarily relies on adsorption and membrane separation technology, in which the high adsorption saturation of adsorbent materials and renewable is the key to adsorption of phosphorus removal, and the physical principle of membrane separation technology is the selective permeability of the membrane. Pollutant retention is achieved through the concentration difference between the two sides of the membrane, hydraulic pressure difference, and potential difference. The current membrane separation technology research methods continue to innovate and generally combine the membrane separation technology and biological method applied to aquaculture tail water phosphorus removal technology. Chemical phosphorus removal technologies such as precipitation, electro-flocculation, crystallization and depth oxidation are important for aquaculture tailwater phosphorus removal technology. These technologies are notable in phosphorus resource recovery and should not be ignored. Biological phosphorus removal technology is a primary method for phosphorus removal in aquaculture tailwater and mainly includes biofilm reactor, Biofloc, microalgae biological purification, bacterial and algal synergistic reactor, artificial wetland and other technologies. Biofilm reactors and Biofloc mainly rely on the role of phosphate accumulating organisms (PAOs) and denitrifying phosphate accumulating organisms (DPAOs), both of which have different processing capacities and biological responses to phosphorus in aerobic, anaerobic and anoxic stages. PAOs absorb phosphorus in aerobic conditions and release phosphorus in anaerobic conditions; DPAOs release phosphorus in anaerobic conditions and absorb phosphorus in the anoxic stage. Microalgae biological purification technology mainly uses the photosynthesis of microalgae and microalgae growth to absorb and remove phosphorus from the water. The microalgae bioreactor is a bacterial-algae synergistic reactor formed by combining microalgae and biofilm reactors to remove phosphorus. Artificial wetlands are a comprehensive phosphorus management method that integrates physical, chemical, and biological methods. This approach is becoming prominent as a crucial technique for phosphorus management in aquaculture tailwater. Current aquaculture modes such as recirculating aquaculture system (RAS), pond aquaculture and other modes, in which RAS mostly use biofilm reactors, bacterial and algal synergistic bioreactors and multi-level integrated aquaculture systems and other treatment methods, and in recent years, artificial wetlands are also gradually applied in the treatment of phosphorus in RAS tailwater. Artificial wetlands are used with sediment and microbial fuel cells to remove phosphorus from aquaculture tailwater. In phosphorus treatment in recirculating aquaculture tailwater, the bioecological method is gradually being used as the main method to treat phosphorus in tailwater, supplemented by physicochemical methods. The pond aquaculture tailwater phosphorus management is also based on bioecological methods, such as ‘three ponds and two dams’, artificial wetlands, multi-level integrated aquaculture treatment system and other methods to remove phosphorus. This study analyzed the aquaculture tailwater phosphorus removal technology, which can provide new ideas for tailwater phosphorus treatment and phosphorus resource recovery and promote the green development of aquaculture.

Abstract:Aquaponics, which is widely considered as an efficient, ecological, and healthy aquaculture mode with notable implications for addressing issues such as aquaculture pollution, freshwater resource scarcity, and aquatic product quality, integrates the aquaculture and hydroponics. The definition of aquaponics remains controversial; however, the key lies in the symbiosis of aquatic animals and vegetables within a single system. Aquaponics encompasses various modes, such as the in situ mode combining pond aquaculture with ecological floating beds and the ex situ mode combining tank-based recirculating aquaculture and vegetable cultivation. Extensive research and discussion have been conducted on system design, aeration and filtration techniques, selection of plants and fish, nutrient balance, environmental control, disease management, and intelligent monitoring, providing technical support for constructing and operating aquaponic systems. Within the aquaponics system, microorganisms are crucial in nutrient transformation and the health of plants and animals, profoundly impacting the ecological balance of the system. Recently, with the rapid development of molecular biology and bioinformatics, genomic techniques such as amplicon-based high-throughput sequencing and qPCR have provided powerful support for analyzing the complex diversity, compositions, and functions of microbial communities in aquaponic systems. Regarding the diversity of microbial communities, studies have indicated higher bacterial community diversity in aquaponic systems than that in aquaculture systems. However, other studies have found no remarkable difference in bacterial diversity between aquaponic and aquaculture systems. Within the aquaponics system, notable differences were observed in the microbial community diversity among different microhabitats. Generally, the bacterial community diversity was the highest in the plant rhizosphere and biofilter and the lowest in the fish feces, with the bacterial diversity in the aquaculture water lying between the two. Various factors drive the spatial distribution of microbial diversity within the aquaponics system, profoundly impacting the functionality of microbial communities and system stability. Additionally, the composition of microbial communities in aquaponic systems are crucial in reflecting system characteristics and indicating the health and growth status of aquatic organisms. The composition of microbial communities in aquaponic systems differed from that in aquaculture and plant growth environments. Studies have identified core microbial taxa comprising bacteria belonging to the genus Bdellovibrio, Luteolibacter, Rhodobacter, and Nitrospira shared in different modes of aquaponic systems. Furthermore, research has shown that dominant bacterial groups vary between different functional units within the aquaponics system. In the biofilter, bacterial taxa belonging to the phylum Actinobacteria were enriched, whereas bacterial taxa belonging to the orders Sphingomonadales and Xanthomonadales inhabited the biofilm of the fish tank. The rhizosphere bacterial communities were dominated by taxa affiliated with the order Methylophilales. Generally, the presence of plants greatly influences the composition of bacterial communities in aquaponics systems. However, the effect of the presence of aquatic animals on plant-related microbial community compositions remains largely unexplored. Regarding microbial functions, nitrogen cycling is one of the most critical elemental cycling processes in aquaponics systems. Establishing efficient “nitrification” functional unit (i.e., biofilters) is a key aspect of system design and construction. The nitrifying microorganisms involved in the nitrification process are considered as beneficial microbial communities in the aquaponics system, typically colonizing the biofilter or the plant rhizosphere environment. For example, aerobic ammonia-oxidizing, anaerobic ammonia-oxidizing, nitrite-oxidizing, and complete ammonia-oxidizing microorganisms have all been detected in aquaponics systems. Additionally, denitrification, nitrogen fixation, and anaerobic reduction of nitrate to ammonium processes have also been identified in aquaponics systems. However, the existing research has primarily relied on taxonomic annotations of amplicon-based sequencing data according to the current database. Whether the nitrogen cycling microorganisms are functionally active and what the contributions of different nitrogen cycling processes are in the aquaponics system remain unclear. Furthermore, research on functional microorganisms involved in the cycling of other elements such as carbon, phosphorus, sulfur, and iron in the aquaponics system lacks, limiting our understanding of the operational mechanisms of aquaponics systems. In aquaponic systems, pathogenic microorganisms that pose risks to the health of fish and pla杮潴慳氠潡晹†灢潥琠敩湮瑴楲慯汤汵祣⁥捤漠湤瑵牲潩汮汧椠湴杨⁥愠煣畯慮灳潴湲極捣⁴獩祯獮琠敡浮獤†瑯桰牥潲畡杴桩浮椠捯牦漠扴楨慥氠⁳浹敳瑴桥潭搮猠⁔楨湥⁩瑲栠敤⁩晳異瑥畲牳敡⹬ and colonization could be facilitated by the water flow in the aquaponics system. Therefore, the prevention and control of pathogenic microorganisms are crucial. One study has indicated that the aquaculture unit of the aquaponic system harbored microbes beneficial for plant health. However, whether these beneficial microorganisms could colonize the plant roots and consequently regulate plant health remain unclear. Additionally, the gut microbiota and rhizosphere microbial communities are key factors in promoting host health. Given the close correlation between the health of fish and plants in aquaponics systems, these host microorganisms interact. However, the interactions between these host microorganisms and host disease resistance in aquaponics systems remain unclear. The microbial communities in aquaponic systems exhibit dynamic characteristics, with their diversity and compositions being jointly influenced by multiple ecological processes. Drawing on microbial ecology theory of community assembly mechanisms and considering the unique features of aquaponic systems, we propose a framework for the formation of microbial communities within aquaponic systems. Abiotic environmental factors, biotic interactions, host selection, dispersal, speciation, and drift processes collectively govern the assembly of microbial communities in aquaponic systems; however, the relative contributions of these processes still require investigation. For a better understanding of the role of microbial communities in the stable and efficient operation of aquaponics systems the distribution characteristics and assembly mechanisms of the diversity, compositions, and functions of different microbial domains in aquaponics systems (e.g., eukaryotic microorganisms) must be systematically investigated. Additionally, the key microbial functional taxa in aquaponics systems and their impacts on the stability and efficiency of the system must be revealed, with the ������������������������������������������������������������������������������������������

Abstract:Monocyclic aromatic hydrocarbons (MAHs), represented by benzene, toluene, ethylbenzene, m/p-xylene, and o-xylene (BTEX), are key components of volatile organic compounds (VOCs). These compounds play crucial roles in the formation of secondary organic aerosols and ozone. BTEX emissions from oceans contribute to localized atmospheric hydroxyl radical reactions and accelerate the formation of secondary organic aerosols. Additionally, as small lipophilic molecules, BTEX can easily penetrate living organisms, leading to unavoidable ecological risks in BTEX-contaminated environments. Due to its proximity to the economically developed Pearl River Delta (PRD) region, the western South China Sea experiences frequent economic activities, particularly fisheries and oil and gas exploration. Rapid development in the PRD region has also established the western South China Sea as a vital shipping channel. Consequently, industrial development and human activities exert pressure on the ecological environment, leading to increased water pollution and risks to fishery resources. However, limited observational data hinder the comprehensive understanding of the sources, spatial distribution, and environmental impact of BTEX in this region. To address this gap, an in-situ investigation was conducted in the western South China Sea and the Pearl River Estuary. Surface and bottom seawater samples were collected from 39 sites, and atmospheric samples were obtained from 16 sites. Temperature and salinity were measured directly during sampling using a CTD. BTEX in seawater samples was analyzed using automatic purge-trap gas chromatography-mass spectrometry (GC-MS), and sea-air fluxes were calculated using Donald Mackay's fugacity model. The ozone formation potential (OFP) and secondary organic aerosol formation potential (SOAFP) of BTEX were also evaluated. The average concentrations of benzene, toluene, ethylbenzene, m/p-xylene, and o-xylene in surface seawater were (12.6±6.3), (79.5±92.8), (10.3±9.6), (21.6±24.1), and (13.4±14.6) ng/L, respectively, showing similar distribution trends. In bottom seawater, these concentrations were (11.2±7.0), (58.0±33.3), (8.2±7.7), (17.3±19.4), and (8.8±9.4) ng/L, respectively. BTEX concentrations in both surface and bottom seawater were consistent with previously reported levels in the nearshore waters of Dalian and the Yangtze River estuary. Significant positive correlations were observed between benzene and ethylbenzene and between m/p-xylene and o-xylene in seawater, suggesting analogous source-sink processes. These compounds are influenced by atmospheric deposition, offshore transportation activities, drilling platforms, and ocean currents. Furthermore, regions with high BTEX concentrations coincided with areas of frequent marine transportation activities, highlighting their impact on marine pollution. The concentrations of BTEX measured in this study were below the acceptable limits established by the World Health Organization (WHO) and the U.S. Environmental Protection Agency (EPA), indicating no immediate threat to marine organisms. Sea-air fluxes of benzene, toluene, ethylbenzene, m/p-xylene, and o-xylene ranged from 8.6–43.8, 71.2–849.4, 4.0–78.9, 1.7–189.0, and 1.1–112.4 g/(km²·d), demonstrating the release of BTEX from the ocean to the atmosphere. Comparison with other coastal areas revealed lower sea-air fluxes in this region, attributed to lower sea surface wind speeds. The mean atmospheric concentrations of benzene, toluene, ethylbenzene, m/p-xylene, and o-xylene were (0.31±0.20), (0.33±0.22), (0.39±0.44), (0.47±0.44), and (0.46±0.46) μg/m3, respectively. Atmospheric BTEX concentrations decreased significantly from inshore to offshore areas, influenced predominantly by continental air masses and volatile transport emissions from surface seawater. The OFP and SOAFP calculations showed that m/p-xylene contributed the most to their formation, necessitating stricter control. Toluene was also identified as a significant contributor to ozone and secondary organic aerosol pollution, consistent with findings from inland areas. However, OFP and SOAFP values in the western South China Sea and the Pearl River Estuary were much lower than those reported in inland regions. This study provides critical data for estimating BTEX emissions and assessing their environmental effects in the western South China Sea and the Pearl River Estuary.

Abstract:The oceans represent a natural source of atmospheric methane (CH4), with estuaries, shelf areas, and near-shore seas collectively accounting for 16% of the global ocean area and contributing approximately 75% of the total annual CH4 release. The release of CH4 from estuaries and near-shore areas is influenced by human activity such as sewage discharge and aquaculture. Hence, it is a scientific priority to study the production and release of CH4 in near-shore aquaculture areas and understand the factors influencing its distribution. Three cruises were conducted in the Yangma Island aquaculture area of the North Yellow Sea at the end of June, and in early and late August 2023. Surface and bottom seawater samples were collected to understand regional dissolved CH4 distribution characteristics, and sea-air fluxes were estimated based on the CH4 concentrations in surface water and wind speeds. The dissolved CH4 concentrations in surface waters obtained during the three cruises during summer were (8.88±4.99), (11.30±4.81), and (9.10±3.03) nmol/L (Mean±SD), and the dissolved CH4 concentrations in bottom seawaters were (14.25±7.99), (16.15±5.93), and (10.88±4.08) nmol/L, respectively. The CH4 concentrations in the bottom water were significantly higher than those at the surface, because of CH4 release from the sediments. The bottom CH4 concentrations were 2~6 nmol/L higher than those in the surface water at most stations at the end of June and beginning of August, owing to the presence of water column stratification, which effectively impeded the transportation of CH4 produced by the sediment, to the upper seawater. By the end of August, the water column stratification had dissipated, resulting in a notable reduction in the discrepancy between the surface and bottom CH4 concentrations. The distribution of dissolved CH4 concentrations in the Yangma Island aquaculture area was predominantly influenced by river inputs, aquaculture activity, and algal and microbial processes. High CH4 concentrations were observed in the nearshore estuaries (Xin'an, Yuniao and Qinshui Rivers) throughout summer due to river input. Dissolved CH4 content in the water body was strongly influenced by aquaculture activity (primarily bivalve shellfish), which provided favorable conditions for CH4 production in the water column, thereby affecting the suspended particulate and organic matter contents in the water column and the sediments. The anaerobic microenvironments of the intestinal tract and excreta of shellfish also represent an optimal setting for anaerobic CH4 production. Consequently, the dissolved CH4 concentration in seawater within the aquaculture zone was markedly elevated compared to that in the non-farming regions. Phytoplankton abundance was high in this area during summer, with Bacillariophyta and Pyrrophyta being the primary groups. Previous studies have demonstrated that the dominant algal species in this area, Leptocylindrus danicus, can directly produce CH4 at a rate of 0.0136 μmol·CH4/(g·dry weight∙h). Moreover, in this study, another dominant algal species, Pseudo-nitzschia, was subjected to laboratory-controlled culture experiments, which demonstrated that it can also produce CH4 at a rate of 46.59 ag/(cell∙d). In addition, some Bacillariophyta and Pyrrophyta indirectly produce CH4 through the degradation of dimethyl sulfoniopropionate (DMSP) released from the algae. Simultaneously, this area showed phosphorus limitation at the end of June and beginning of August, and the high DOC content in the aquaculture area provided rich C-P bonds, allowing microorganisms to degrade organic phosphorus compounds to produce CH4. In early August, the ∆CH4 concentration in the surface layer had a significantly positive correlation with Chl-a, verifying that aerobic processes such as phytoplankton production and methyl compound degradation can provide ΔCH4 sources in aerobic surface waters during summer. Spatiotemporal variations in CH4 saturation and air-sea fluxes in the surface seawater showed trends of aquaculture area > non-aquaculture area and bay area > coastal shelf area. The CH4 saturation in the surface water obtained during the three cruises in the coastal waters adjacent to Yangma Island aquaculture area during summer were (377±209)%, (527±224)% and (391±130)%, respectively, and were all oversaturated with respect to atmospheric CH4. The air-sea exchange flux (estimated using the W2014 relationship) of CH4 in the surface water during summer was (18.87±28.82) μmol/(m2∙d). Overall, we estimated the annual CH4 emissions from the coastal waters adjacent to Yangma Island aquaculture area to be approximately 5.87×10-5 Tg/yr, indicating that this region is a net source of atmospheric CH4.

Abstract:In recent decades, eutrophication, harmful algal blooms, and seasonal hypoxia in the bottom water have been frequently reported in Chinese coastal waters owing to excessive human-induced nutrient input. Phosphorus (P) is an essential biogenic element for marine phytoplankton and is important in eutrophication and harmful algal blooms of the estuarine and marine ecosystems. Sediment has a buffering effect on the P concentration in the overlying water and is an important P source for sustaining pelagic primary production. In addition, the cycling and release of P in sediments play a notable role in maintaining the water trophic status. The biogeochemical cycle of P in sediments is a key topic in marine science worldwide. Understanding the adsorption and desorption behaviors of P in sediments is necessary to comprehend P cycling and assess its potential release risk in estuarine and coastal environments. Maowei Sea is a typical tropical bay with high density oyster aquaculture where industrialization and urbanization have synchronously altered the natural ecosystem structure and marine ecological environments in northern Beibu Gulf. It is part of the Silk Road Economic Belt and the 21st-Century Maritime Silk Road, which have become an important part of the national developmental strategy of China. Human activities have affected the Maowei Sea’s ecological environment, particularly in the main estuaries of the Maowei Sea. Consequently, the average N/P molar ratios are much higher than the Redfield ratio of 16 : 1. P has become the limiting element for phytoplankton growth in the study area. The adsorption and desorption of P in sediments play an important role in the dynamic cycling of P in aquatic ecosystems. However, compared to other coastal and estuarine regions worldwide, geochemical information about P adsorption behavior characteristics in surface and core sediments in the main estuaries of the Maowei Sea has been largely ignored. The sediment acts as the “sink” or “source” of P in water through the behaviors of P adsorption/desorption, which has a significant impact on marine primary productivity and water eutrophication. However, the characteristics of the P adsorption behavior of core sediments in the estuaries of the subtropical bay remain unclear. The core sediments of the two main estuarine regions in the Maowei Sea were analyzed to examine the effects of different sediment particle sizes and salinity on sedimentary P adsorption behavior through adsorption kinetics and isothermal adsorption experiments. P speciation in the sediments before and after adsorption experiments was quantified using the improved sequential extraction (SEDEX) method, and the P adsorption mechanisms in sediments were explored. The results showed that the adsorption kinetics of P in sediments could be described by a fast and slow two-stage first-order kinetic equation, and the adsorption isotherms fitted the modified Langmuir-crossover model. The adsorption capacity of P in the sediments at different depths of the same station was relatively different, and the desorption behavior existed on both sites when the initial P concentration was low. Sediments with smaller particle sizes had a high adsorption capacity for P. The increase in salinity reduced the adsorption capacity of P in sediments, indicating that low salinity facilitated P adsorption in sediments. Exchangeable P (Ex-P) and iron-bound P (Fe-P) contents increased significantly in sediments after adsorption. The adsorption processes of P in sediments included physical and chemical adsorptions, with physical adsorption being the main process. The results may provide valuable information for further research on the P biogeochemical cycle and ecological effect, as well as contribute to the development of the beautiful bay construction and sustainable growth of the marine economy.

Abstract:Green tides, dominated by Ulva prolifera, have occurred each summer in the Yellow Sea of China from 2007 to 2023 and are characterized by a huge biomass, long duration, and extensive influence areas. During the post-bloom period, millions of tons of U. prolifera settle to the sea floor and release carbon, nitrogen, and phosphorus into the surrounding waters, notably impacting coastal environments. Organic matter released from macroalgae are important contributors to biogeochemical cycles in marine ecosystems. Particulate organic carbon (POC) is an important fraction of the marine organic carbon pool and is crucial in the marine carbon cycle by regulating dissolved organic carbon (DOC); sediment organic carbon; and inorganic carbon via deposition, degradation, and mineralization. Additionally, the ratio of POC and particulate organic nitrogen (PON) affects the sea-air CO2 flux and the efficiency of carbon sequestration. Till date, POC and PON released during the degradation of U. prolifera remain poorly quantified and microbial regulations of POC and PON release remain unclear. We investigated the changes in POC and PON concentrations and their molar ratios, and microbial abundance under different degradation densities (1 g/L and 5 g/L) during a 90-d laboratory degradation of U. prolifera. Under dark conditions, 50 g and 250 g (fresh weight) of U. prolifera were added to polyethylene carboys containing 50 L filtered seawater to conduct 1 g/L and 5 g/L degradation experiments. Triplicate replicates were performed for each treatment. Samples for analyzing POC, PON, and microbial abundance were collected on days 0, 4, 6, 8, 14, 21, 28, 60, and 90. The results showed that the degradation period of U. prolifera was divided into the leaching stage (0–14 d), during which soluble materials were lost, and the microbial degradation stage (14–90 d), during which the debris was digested by bacterial or fungal extracellular enzymes. The POC, the maximal values: (90.17±24.77) μmol/L and (219.99±45.11) μmol/L under 1 g/L and 5 g/L, respectively, and PON, the maximal values: (16.15±0.71) μmol/L and (23.20±7.16) μmol/L under 1 g/L and 5 g/L, respectively, concentrations changed significantly during degradation, however, showed different trends. Specifically, the POC and PON concentrations first increased and then decreased during days 0–60; however, POC continued to decrease (approximately 49%) and PON increased (approximately 430%) during days 60–90. The decrease in POC concentrations can be explained by the conversion of POC to DOC by macroalgae-associated microbes and subsequently, DOC was mineralized into dissolved inorganic carbon. The enrichment of nitrogen due to bacterial colonization of particle surfaces may largely explain the increase in PON concentrations. POC:PON first increased and then decreased, indicating that PON showed a lagged release compared to POC when U. prolifera began to degrade, and the subsequent decline of POC:PON can be attributed to nitrogen fixation by microbial and carbon consumption via respiration. Microbial abundance increased during days 0–28, the maximal values: (9.81±3.81)×105 and (26.24±6.98)×105 cells/mL under 1 g/L and 5 g/L, respectively, indicating that the released organic matter was utilized and transformed into microbial biomass. The microbial abundance then decreased during days 28–90. This change may be explained by the decrease in organic matter contents and bioavailability, and the contents of organic matter were deficient for microbial growth, leading to the decrease in microbial abundance. Microbial abundance showed significant correlations with the POC and PON concentrations, indicating the critical roles of microbes in the release of POC and PON during the degradation of U. prolifera. No significant correlations were observed between the microbial abundance and POC:PON. Microbial regulations of POC and PON release during the degradation of U. prolifera are complex and further studies on microbial community structure may help to explore the role of microbes in the release of POC and PON. Degradation density significantly impacted POC and PON concentrations. At the high degradation-density treatment, we observed slow changes in POC and PON concentrations and 2–3 times higher maximal concentrations of the two compared to those at lower degradation-density conditions. We observed that the higher the degradation density, the longer the leaching phase of organic matter. However, POC and PON concentrations did not change proportionally with degradation density. This result may be attributed to the changes in other factors such as pH, dissolved oxygen, and initial nutrient concentrations. The changes in POC and PON concentrations at the end of degradation suggested that more extensive studies are necessary to elucidate the long-term relationship between U. prolifera degradation and microbial communities. Our study provides an important basis for clarifying the changes in POC and PON and their correlations with microbial abundance during the degradation of U. prolifera. This helps to generate a better understanding of the regulation and mechanisms of microbes on U. prolifera degradation.

Abstract:Estuarine ecosystems play an important role in biodiversity due to the close interrelationship between riverine and marine environments. Phytoplankton and zooplankton serve as ecological indicators of water quality in estuarine ecosystems. Therefore, an integrated evaluation of the effects of multiple environmental factors on the phytoplankton and zooplankton communities in estuarine ecosystems is essential. Previous studies have often been limited to the interaction between a single phytoplankton or zooplankton species and environmental factors, whereas studies on the mechanism of the overall planktonic response to environmental factors are lacking. Therefore, we collected water samples from seven stations in the waters of the Liuqinghe Bay in March (spring), August (summer), and October (autumn) 2021. Redundancy analysis and Pearson’s correlation analysis were used to explore the effects of environmental factors on dominant phytoplankton and zooplankton species and communities. The results showed that there were large seasonal differences in water temperature in the study area, with the highest (23.70±0.17 °C) in summer and the lowest (5.91±0.03 °C) in spring. Changes in the mean salinity of offshore estuarine waters—with variations ranging from 30.29 to 31.70—were usually caused by inputs from estuarine runoff, showing obvious seasonal characteristics, and salinity among different stations did not show significant differences. The pH decreased with increasing water temperature. Compared with the first three hydrological parameters, chemical oxygen demand, Chl a, and nutrient salts did not show obvious seasonal patterns. In 2021, 94 phytoplankton species from three phyla were identified during the three cruises, with 80 Bacillariophyta spp. being the most abundant, followed by 13 Pyrrophyta spp. and 1 Chrysophyta sp.—it is worth mentioning that the same Chrysophyta sp. was identified in all the 3 cruises. The spring cruise in 2021 identified 44 species from three phyla, the summer cruise had the richest community composition, with 58 species from three phyla, and the autumn cruise identified 55 species from three phyla. In addition, the mean abundance of phytoplankton in Liuqinghe Bay in 2021 reached its maximum in summer (242.50×103±136.40×103 cells/m3), with the mean abundance in spring (19.38±12.23 cells/m3) at the lowest level. However, the seasonal variation of mean phytoplankton biomass in 2021 in Liuqinghe Bay showed the same abundance trend, with a maximum carbon biomass (946.89±810.66 µg C/m3) in summer and the lowest carbon biomass (31.15±20.96 µg C/m3) in spring. A total of 48 zooplankton species were identified in 10 groups, with copepods being the most numerous (15 species), followed by pelagic larvae and hydroidomedusa (11 species each), tunicates (3 species), chaetognaths and cladocera (2 species each), and one species each of jellyfish, amphipoda, mysidacea, and euphausia. A total of 14 zooplankton species from five taxa were identified during the spring cruise, 28 species from seven taxa during the summer cruise, and 25 species from eight taxa during the autumn cruise. Copepods and pelagic larvae had the highest occurrence frequency in the samples from each seasonal cruise; however, the frequency of Hydroidomedusae gradually increased over time. Moreover, the mean zooplankton abundance in the study area showed a clear seasonal pattern ranging from (55.00±12.52) – (5 665.71±4 576.32) ind./m3, with the maximum and minimum mean abundances in spring and autumn, respectively. Biomass exhibited a seasonal pattern like that of abundance, showing an overall decreasing trend. In 2021, the phytoplankton Shannon–Wiener diversity index (H′) and Pielou’s evenness index (J) in Liuqinghe Bay varied greatly among the three seasons, and there were significant differences among different stations. The average J of phytoplankton did not differ significantly among seasons, especially in spring and summer, but it fluctuated greatly among different stations. In general, phytoplankton biodiversity was the highest in summer and lowest in spring, whereas the evenness index was relatively evenly distributed in spring and summer and more scattered in autumn. The zooplankton H′ and J showed very similar trends, being generally higher in summer and autumn than in spring, and the H′ fluctuation in summer and autumn was also stronger than that in spring. The overall trend was higher in the summer than in the autumn. Overall, there were significant spatial and temporal variations in plankton in Liuqinghe Bay, in which the main influences on plankton-dominant species in spring and summer were temperature and nutrient salt concentration, while the main drivers affecting plankton-dominant species in autumn were temperature, salinity, and nutrient salts, and there was a potential for red tides to occur in spring and autumn. In addition, ocean currents, land runoff, and meteorological hazards are important factors that influence the community composition of dominant zooplankton species. The results of this study will help improve the understanding of plankton communities in estuarine ecosystems. It will also provide a theoretical basis for the scientific management of the ecological environment of Liuqinghe Bay and an in-depth understanding of the mechanisms of plankton community changes in the Bay.

Abstract:Ecosystem integrity is the foundation of ecosystem health and is popular to quantitatively analyze ecosystem integrity using the Index of Biotic Integrity (IBI). The IBI was initially used as a water pollution index and has been widely applied in ecosystem health assessment, particularly in fish, benthos, and plankton. Phytoplankton is the primary producer in aquatic ecosystems and is sensitive to changes in environmental factors. The Phytoplanktonic IBI (P-IBI) has been increasingly used in the ecosystem health assessment of bays, rivers, lakes, and reservoirs. However, no reports are available on applying P-IBI in the estuary ecosystem. Based on P-IBI, this study constructed an ecological health assessment indicator system and built an evaluation criterion in the coastal waters of the Yellow River estuary. To evaluate the ecological health status, three surveys were conducted on phytoplankton in May, July, and December of 2020. A total of 31 sampling sites were set up in the study area (119°00′E–119°25′E, 37°20′N–38°05′N), and 73 species of phytoplankton from four phyla were collected, with diatoms being the major groups and the species number accounting for 82.19%. The reference points and damaged points were determined according to the Shannon-Wiener diversity index H´, and the sites with H´≥3 were reference points; the others were damaged points. Considering factors such as ecological characteristics of the study area, phytoplankton population distribution, and data availability, 13 biological indicators were selected as candidate indicators. Then, the core indicators of P-IBI in various months were identified by screening candidate indicators. First, the discriminant ability analysis was used to preliminarily select the indicators, and their IQ≥2 were retained. Second, Pearson correlation analysis was conducted for these indicators. The P-IBI core indicator system in May, July, and December contained four, five, and four biological indicators, respectively. The scores of each indicator were calculated using the ratio method. The 95% or 5% quantile of the core indicators in all sampling sites was regarded as the best expected value; for indicators which increased with increasing interference, the best expected value was 5% quantile. Conversely, for indicators which decreased with increasing interference, the best expected value was 95% quantile. Each indicator score was calculated using a different formula according to their response to interference. Accumulating all core indicator scores at the same site, the total P-IBI score for this site was obtained. The 25% quantile of the reference points P-IBI was taken as IBI-expected, the P-IBI range less than IBI-expected was quartered. The delineation standard for the ecological status grade was ascertained, and the ecological status level of each site was identified according to its total P-IBI. The ecological status of each site was marked by using 1, 3, and 5 approximations of value assignment, the marked scores of each site were summed up using the equal weight method, and standardization was conducted to eliminate the differences caused by various indicator numbers. The comprehensive evaluation index (CEI) of the coastal waters in the Yellow River estuary was achieved. The results showed that the ecological status in each site was different and the spatial distribution was significantly diverse for the three months. In May, a few sites were present with excellent levels (9.68%), and they were scattered around the mouth of the Yellow River. In July, the proportion of sites with excellent levels reached 35.48%, and they were mainly located in the estuary of the Yellow River and Laizhou Bay. In December, the proportion of sites with excellent status was approximately 38.71%, and they were concentrated in the waters north of the Yellow River estuary. In general, concerning the stations above “good” ecological level, 21 were present in May; 29, in July; and 26, in December; therefore, the ecological condition was slightly worse in May. P-IBI had a significant positive correlation with ammonium (NH4-N), a significant negative correlation with nitrate (NO3-N), phosphate (PO4-P), and dissolved oxygen (DO), and a significant positive correlation with sea surface temperature (SST). However, no significant correlation was observed between P-IBI and sea surface salinity (SSS), pH value (pH), nitrite (NO2-N), and silicate (SiO3-Si). The CEI indicated the health status was “fair” in the coastal waters of the Yellow River estuary in 2020. Selecting reference points and screening biological parameters were the key steps in constructing the P-IBI indicator system, which determined the science of the evaluation result and the practicality of regional health management. The detailed method was offered in this study, and it could provide information for other research projects. This study provided a reference for the health management and ecological restoration of this water area and offered data support for the ecological protection and high-quality development of the Yellow River Basin.

Abstract:Mudflats, located at the land-sea interface, are extremely rich in ecological resources. They are an important spatial carrier for human survival and development and are notably influenced by human activities. The rapid social and economic development of coastal areas has led to increased pollutants being discharged into the coastal waters with water flow, which seriously affects the coastal aquatic ecological environment. Sediment is the sink for most pollutants, including nutrients, heavy metals, and organic compounds. Pollutants can be enriched in sediments through physical changes such as adsorption, accumulation, and precipitation. When the water environment conditions change, the pollutants in sediments are released into the overlying water, affecting the aquatic ecosystem's health. Biological activities destroy the physical structure of the sediment-water micro-interface, change the oxygen content at the interface, induce the movement of sediment particles, bring the interstitial water out of the sediment interface, and promote the release of heavy metals in the sediments. Heavy metal pollutants are inherently toxic, persistent, and difficult to degrade, leading to many serious environmental problems and posing significant health risks. Therefore, evaluating the risk of heavy metal pollution in surface sediments as an important reservoir of heavy metal pollutants is necessary. This provides a scientific basis for the ecological management and restoration of mudflats. Presently, most studies on heavy metal pollution in the sediments of Rudong mudflats focus on the source of heavy metal elements and the evaluation of biotoxicity. Studies on the correlation analysis of the distribution characteristics of heavy metals in the Rudong mudflats and the distribution characteristics of benthic animals in the Rudong mudflats are scarce. In this study, the distribution characteristics of seven heavy metal elements in the sediments of the Rudong Meretrix meretrix aquaculture area were analyzed, and the potential ecological risk index method was used to evaluate the environmental risk of heavy metals in the sediments of the aquaculture area. Meanwhile, the correlation analysis between the distribution of zoobenthos and heavy metal pollution was performed to provide a reference for the ecological environment of the M. meretrix mudflats in Rudong and the sustainable development of the clam mudflat resources. Four field surveys were conducted in September and December 2022 and April and July 2023 in the M. meretrix mudflat aquaculture area in Rudong, Jiangsu Province. The contents of Zn, Cr, Cu, Pb, As, Hg, and Cd in the surface sediments were determined, and the characteristics of benthic communities were analyzed. The pollution risk assessment of heavy metals in surface sediments was conducted using the potential ecological index method, and the response relationship between heavy metal pollution in sediments and the distribution of benthic animals was analyzed. The results showed that the average contents of heavy metals in the surface sediments were in the order of Cr>Zn>Pb>Cu>As>Cd>Hg, and the contents of Zn, Cu, Pb, As, Hg, and Cd were in accordance with the quality standard of one type of marine sediments. The highest value and summer average value of Cr exceeded the first-class standard of marine sediment quality and met the second-class standard of marine sediment quality. The annual comprehensive potential ecological risk index ranged from 90.49 to 145.78, averaging 110.68. Regarding the classification of potential ecological risk, the overall risk level of the M. meretrix aquaculture area was at the medium risk level, and the order of individual potential ecological risk of each heavy metal element was Cd>Hg>As>Pb>Cu>Cr>Zn. The ecological risks of each sampling station were mainly from Cd, Hg, and As. Sampling was performed four times. The heavy metal Cd was the primary contributor to potential ecological risk and sediment pollution in the Rudong mudflats. Cd, Hg, and Cu are important components of industrial sewage discharge, and the land-based inputs and other pathways are their main sources. As is uncommon in natural environments, it is a primary component of chemical fertilizers and pesticides. The use of pesticides in the mudflat shellfish aquaculture area may be the main source of the As pollution. Most of the Pb in the sediments originates from atmospheric deposition and is linked to the pollution emission of fishing ports and ships in the region. Zn is related to the zinc plating and machinery manufacturing industries, while Cr is applied in large quantities in the chemical and chromium-plating industries. A total of 68 species of macrobenthos were collected in the four samplings. The richness index d ranged from 0.74 to 5.01 (SD=±1.19), the evenness index J' ranged from 0.25 to 0.92 (SD=±0.15), and the diversity index H' ranged from 0.99 to 3.79 (SD=±0.65) at each sampling station. The mean values of the diversity index H' for spring, summer, autumn, and winter were between 2 and 3, respectively. Compared with the biodiversity index evaluation criteria, the biodiversity of the four seasons belonged to a relatively rich level, and the habitat level was at a 'general' level. The density of polychaetes in the benthic animals had a significant negative correlation with Cu, Pb, Cr, and Cd heavy metal element index and RI. A significant negative correlation existed between the benthic animal richness index d and the heavy metal element indexes of Pb, Cr, and As.

Abstract:From 1990 to 2020, red tides of Alexandrium tamarense—which produces paralytic shellfish toxins (PSTs)—were monitored in the waters of the Nanhuangcheng Island Sea area in Changdao County, China, with a cumulative affected area of 2.37 km2. PST-producing Gymnodinium spp. were also detected in the Yantai Sishili Bay and Weihai coastal waters, with a cumulative affected area of 48.88 km2. In 2020, lipophilic shellfish toxin (LST)-producing Dinophysis spp. were detected in the North Yellow Sea. In 2021, amnesic shellfish toxin (AST)-producing Pseudo-nitzschia was detected in small quantities in the typical Patinopecten yessoensis culture area of Zhangzi Island and Yantai Sishili Bay in the North Yellow Sea. PSTs, LSTs, ASTs, and their toxin-producing algae are widely found in the Yellow and Bohai seas. Shellfish and phytoplankton samples were collected from waters off Changdao Island from June to October 2023, and screened for 29 shellfish toxins, including 14 PSTs, 14 LSTs, and domoic acid (DA). PSTs and LSTs were detected throughout the survey period, whereas DA was not. The main detected components of PSTs were GTX1, GTX2/3, C1, and C2, while LSTs were detected less frequently and at low concentration, and PTX2 was detected only in the Chlamys farreri sample of June (2.46 μg PTX2eq./kg SM), which is much lower than the current EU safety limit of 160 μg PTX2eq./kg SM. As the risks of DA and LSTs in the sea area around Changdao Island were low in this study, we focused on analyzing the pollution characteristics and potential sources of PSTs. None of the PSTs detected in the shellfish samples from June to October exceeded the EFSA safety limits. The GTX2, GTX5, C1, and C2 of PST components were detected, with GTX2 being the highest detection rate of 53.3 %, and C1 being the maximum concentration of 179 μg/kg. Among the shellfish samples collected during the entire survey period, PSTs were not detected in Mytilus galloprovincialis and Crassostrea gigas in June and August, and in all shellfish samples collected in July. PSTs were detected in Chlamys farreri in September at 478 μg/kg, the highest concentration among all the months, followed by Chlamys farreri in October at 221 μg/kg. Among the phytoplankton samples, PSTs were detected at stations S2, S3, and S4 in September and at stations S1 and S2 in October, with relatively low concentrations of PSTs. PSTs were not detected in other months or stations. The highest level of PSTs in phytoplankton was 23.92 μg/L at station S2 in September, and the average level was 20.7 μg/L. The average PST level in October was 2.67 μg/L. In October, only two components were detected at stations S1 and S2—dcGTX3 and GTX4. In September, PSTs were more abundant, with seven components: GTX1/4, GTX2, dcGTX3, GTX5, and C1/2. High-throughput analysis of phytoplankton revealed the presence of eight Alexandrium spp. with the highest abundance of Alexandrium spp. in September. Alexandrium spp. cysts were found in the sediments in September, which suggests that the toxicity-producing algae of PSTs in the Changdao Island waters in the present study may be Alexandrium spp. Although PST concentrations in the samples off Changdao Island were relatively low compared to other regions in the Yellow Sea and Bohai Sea, there is still a potential risk of PST contamination. To guarantee the quality and safety of aquatic products, monitoring of shellfish toxins should be strengthened to provide basic data for the early warning of toxin contamination in aquaculture areas.

Abstract:Perfluorooctanoic acid (PFOA) is a synthetic organic chemical with unique hydrophobic and oleophobic properties. It is extensively used in the production of a wide range of essential industrial and consumer products including aqueous film-forming foams, medical devices, and textiles. PFOA is widespread in aquatic environments and has attracted global attention due to the serious ecological risks it poses. Consequently, several countries and organizations have implemented strict restrictions or controls on its use. In 2019, PFOA and its salts were included as Annex A of the Stockholm Convention on Persistent Organic Pollutants, and in 2023, the Ministry of Ecology and Environment of the People's Republic of China and six other departments issued the "Key Regulated New Pollutant List 2023", which proposed environmental risk control measures for PFOA, its salts, and related compounds. With an increase in regulatory measures, the production and use of PFOA have declined, resulting in the rapid development and use of alternatives. Hexafluoropropylene oxide dimer acid (HFPO-DA), trimer acid (HFPO-TA), and tetramer acid (HFPO-TeA)—composed of CF2 or CF2O repeating units—have emerged as principal alternatives that maintain chemical properties similar to those of PFOA and are predominantly used in the manufacture of fluoropolymers and their processing aids. As filter-feeding organisms, bivalves are prolific and have a broad geographic distribution. They possess a marked capacity for accumulating organic contaminants, making them ideal indicators for monitoring pollution in marine environments and assessing the status of various marine ecosystems. Therefore, Manila clams (Ruditapes philippinarum) were used as the test organism in this study and exposed to two concentrations (2 ng/mL and 200 ng/mL) of PFOA and its alternatives—HFPO-DA, HFPO-TA, HFPO-TeA—within a mariculture setting. The purpose of this study was to analyze the tissue distribution, accumulation, and elimination patterns of these compounds in clams, and to evaluate differences in the accumulation ability of organisms to enrich PFOA and its ether carboxylic acid alternatives in clams by calculating kinetic parameters. Additionally, water-soluble proteins were extracted from the visceral masses and gills of the clams and incubated in vitro to explore the differences in binding rates between the target compounds and clam proteins. The binding modes between the target molecules and proteins were investigated using molecular docking techniques to further elucidate the relationship between molecular and protein interactions and the bioaccumulation properties of clams. It was found that that PFOA and its ether carboxylic acid alternatives were rapidly enriched in Manila clams. The enrichment rate of targets increased as HFPO-DA < PFOA < HFPO-TA < HFPO-TeA, and the enrichment effects in different tissues were visceral mass > gill > mantle > adductor muscle. After a 21-day depuration period, the contaminant levels in Manila clams approached those in the control group. Furthermore, in Manila clams, the accumulation capacity of PFOA and its alternatives, and the binding rates of different target molecules to body proteins were strongly correlated with the target concentrations. Lower target concentrations led to greater absorption rate constants and bioconcentration factors and lower binding rates of the targets to the protein. The target content and protein binding in each tissue were HFPO-DA < PFOA < HFPO-TA < HFPO-TeA. Additionally, the molecular structure of PFOA and its alternatives—particularly the increase in C-O bonds and C-F chains—enhanced their binding affinities with protein residues. The binding forces between PFOA, its alternatives, and the fatty acid-binding protein FABP1-A were further validated by molecular docking studies. The magnitude of the binding energy was HFPO-TeA < HFPO-TA < PFOA < HFPO-DA, and the lower the binding energy, the easier it was to bind to the protein. The polar ends of the targets formed hydrogen bonds with the amino acid residues of FABP1-A, whereas their hydrophobic ends engaged in hydrophobic interactions with nonpolar residues, collectively enhancing the protein binding of PFOA and its alternatives. The number of hydrogen bonds is also an important cause of binding affinity differences in the target proteins. This study elucidates the bioaccumulation behavior of PFOA and its alternatives in bivalves and provides a scientific basis for the control and management of emerging contaminants. Although the levels of PFOA and its alternatives in aquatic environments are currently traceable, the ecological risks associated with their persistence in the environment should not be underestimated. Moreover, the findings on their binding rates to clam proteins offer a scientific basis for the reasonable selection of alternatives. Additionally, the molecular docking data furnish a theoretical basis for investigating the specific binding of PFOA and its alternatives to proteins with different carbon chain lengths and structures.

Abstract:Fish play an important role in maintaining aquatic ecosystems and directly affect the health and stability of aquatic ecosystems. The rapid economic development of the Wanquan River basin has seriously affected the ecological function of fish in the basin owing to human activities such as dam dredging and highways. Therefore, long-term surveys and monitoring of fish diversity are urgently required to determine the current status of fish resources in the basin and formulate corresponding conservation measures. Traditional fish surveys primarily use gear fishing methods, such as gillnets, purse seines, and ground cage nets. However, traditional fishing gear survey methods have limitations, particularly because different gears are selective for fish species and individual sizes. Catching fish species that are small in number and elusive is challenging, making it difficult to accurately and comprehensively monitor the fish diversity in the survey area. In addition, the restriction of the fishing moratorium further increases the difficulty of traditional operational surveys. Therefore, a rapid and effective monitoring method is urgently needed to study the fish resources of the Wanquan River. Environmental DNA (eDNA) technology involves analyzing biological communities by enriching DNA retained in the environment and using high-throughput sequencing technology. This method offers several advantages, including minimal environmental disturbance, time and effort efficiency, and allowing rapid monitoring of fish diversity and spatial distribution. eDNA technology has been widely used in biodiversity monitoring, population distribution, biomass assessment, and feeding analysis. To investigate the fish diversity and community structure in the Wanquan River Basin, this study used eDNA technology in combination with the traditional fishing gear survey method for comparative analysis and explored the advantages of the two methods in fish monitoring. The results showed that 76 species of fish in six orders, 32 families, and 65 genera were detected by eDNA technology, whereas 44 species in four orders, 14 families, and 44 genera were detected by the traditional fishing gear survey method. Overall, the eDNA method detected more fish species than the traditional survey method at all sampling sites. The dominant fish species detected by both methods were Carpiformes, followed by Perchiformes and Siluriformes. In terms of the composition of dominant species, 22 dominant species of fishes in Wanquan River were detected by eDNA technology, seven dominant species were detected by the traditional survey method and two dominant species were detected by the two methods, which were Coptodon zillii and Toxabramis houdemeri. Alpha-diversity analyses indicated that the fish species richness detected by the eDNA method was significantly higher than that of the traditional method, whereas the evenness was higher than that of the traditional method. The principal coordinate analysis (PCoA) results revealed that the fish composition at the HP sampling site was less similar to that of the DLQ, JJ, PL, and DBQ sampling sites, with fewer common species. Spearman's correlation analysis showed that eDNA technology and traditional survey methods had a significant positive correlation (P<0.05) between species sequence abundance and fish quality. This preliminary exploration of the fish diversity of Wanquan River using both the eDNA and traditional survey methods establishes a particular foundation for the application of eDNA in monitoring the fish diversity of Wanquan River and also serves as a reference for the protection of the fish management of Wanquan River.

Abstract:Seawater recirculating aquaculture is a sustainable aquaculture method that provides benefits such as the conservation of water and land resources, high productivity, and environmental protection. The high NO3–-N concentration in wastewater is a primary factor limiting wastewater discharge to meet compliance standards and restricting the sustainable development of seawater recirculation aquaculture. Biological denitrification is the primary method for removing NO3–-N in the water. Sulfur autotrophic denitrification (SAD) does not require an external organic carbon source and produces low sludge production, making it suitable for treating seawater recirculating aquaculture water with lower C/N ratios. However, SAD generates H+, which reduces the pH of water, thus affecting the stability of the denitrification device in long-term operation. In the actual operation of the SAD device, oyster shells are frequently used as a filler substrate to regulate the pH of water and ensure the effectiveness of the device in denitrification. Oyster shells, as kitchen waste, are cheap and easy to obtain and have received widespread attention. Studies on the denitrification performance and microbial community structure of the SAD device for marine recirculating aquaculture wastewater with varying hydraulic loading rates (HLRs) and S0/Oyster shell filling ratios are limited. In this study, we compared the denitrification performance of SAD devices with three S0/Oyster shell ratios (5:1, 3:1, and 1:1) under five HLRs [0.19, 0.24, 0.32, 0.48, and 0.95 m3/(m2·d)] and the changes in influent and effluent pH and DO in the treatment of seawater recirculating aquaculture wastewater, using artificial seawater recirculating aquaculture wastewater as the treatment target. The effects of different S0/Oyster shell ratios on the nitrogen removal performance of the SAD device were evaluated in combination with microbial community characterization and functional gene prediction analysis. When the HLR was 0.19~0.48 m3/(m2·d), no significant difference was observed in the NO3–-N removal rates among the four HLRs and three devices, which were (72.11±12.64)%~ (75.85±7.95)%, (76.00±6.91)%~(78.13±6.45)%, (70.40±7.78)%~(75.76±8.98)%, respectively. At the highest HLR [0.95 m3/(m2·d)], the NO3–-N removal efficiency of the three devices significantly decreased, and the NO3–-N removal efficiency of the S0/Oyster shell=5:1 (61.16%±9.31%) and 3:1 (56.62%±7.23%) devices was significantly higher than that of the S0/Oyster shell=1:1 (38.98%±10.19%). For the S0/Oyster shell=3:1, the average concentration of effluent NO2–-N of the device was the lowest at (0.59±0.39) mg/L. No significant difference was observed in the average concentration of effluent NH4+-N among the three devices, ranging from (0.17±0.07) to (0.19±0.11) mg/L. The denitrification performance of S0/Oyster shell=5:1 and 3:1 devices was better. The effluent pH of the device decreased with increased S0/Oyster shell ratio and HLR. The dominant bacterial phyla in the SAD device were Campilobacterota (6.47%~59.73%) and Proteobacteria (16.46%~53.93%), and the dominant bacterial genus was Sulfurimonas (2.70%~49.50%). As the ratio of S0/Oyster shells decreased, the abundance of Sulfurimonas increased within the device and at the intersection of oyster shells and S0 in the upper part of the device. pH was positively correlated with denitrification gene abundance. This study provides basic theoretical data for the design and operation of SAD devices in seawater RAS.

Abstract:Over 80% of marine litter is composed of plastic waste, which reaches the oceans via atmospheric transport, surface runoff, and human activities such as shipping and fishing. These plastics degrade into microplastics (MPs)—prevalent environmental pollutants <5 mm, which possess a “carrier effect”, enabling them to adsorb contaminants such as heavy metals. CuSO4—frequently used in aquaculture to manage diseases and cyanobacterial blooms—can introduce excess Cu2+ into aquatic environments, adversely affecting water quality and aquatic life. The Chinese mitten crab (Eriocheir sinensis) is vital to freshwater aquaculture in China. Mature E. sinensis migrate to the Yangtze River estuary annually for reproduction; however, estuarine ecosystems are becoming increasingly disturbed, making mitten crabs vulnerable to MPs and heavy metal contamination. The intestinal tract, which directly interacts with ingested pollutants, is particularly susceptible. Previous studies have examined MP or Cu2+ effects on E. sinensis independently, however, their combined effects remain underexplored. Here, MPs (0.4 mg/L) and Cu2+ (0.1 mg/L) were selected as the experimental concentrations with four treatment groups: Group M (0.4 mg/L MP-exposed); Group C (0.1 mg/L Cu2+-exposed); Group MC (0.4 mg/L MP + 0.1 mg/L Cu2+ combined-exposed; and Group D (blank control group) to investigate the effects of MPs and Cu2+ on the intestinal tract of E. sinensis after 21 days of single and combined exposure. Transcriptome sequencing of the intestinal tissues was conducted using Illumina's high-throughput platform, generating 197,908,972 raw reads. Post-quality filtering yielded clean reads across the four groups, with 94.71%–95.48% Q30 scores. In total, 109,644 transcripts were identified, with 68,005 exceeding 1800 bp in length. Differential expression analysis revealed 1,650 and 1,874, 3,797 and 1,073, and 1,492 and 1,305 upregulated and downregulated differentially expressed genes (DEGs) in Groups M, C, MC, respectively. Notably, DEGs associated with antioxidant defense, immune response, and energy metabolism differed significantly among the comparison groups. Catalase (cat) and peroxiredoxin (prdx) were downregulated, whereas trim, toll-like receptor (tlr) and complement component 1 (c1) were upregulated in the immune system. Cytochrome P450椠猨⁣獹瑰甴搵礰⸩†呷桡敳†牳敩獧畮汩瑦獩⁣潡普⁴瑬桹椠獤獷瑮畲摥祧⁵牬敡癴敥慤氠敡摣⁲瑯桳敳†浴敨捥栠慴湲楥獡浴獭⁥潮晴†䵧偲獯⁵慰湳搮†䍅畮㉥⭲❧獹†敭晥晴敡换瑯獬⁩潳湭†瑄桅敇⁳愠湡瑬楳潯砠楶摡慲湩瑥Ɽ‬椠海浩畴湨攠⁣摡敲晢敯湮捩散Ⱐ⁡慮湨摹⁤敲湡敳牥朠礨⁣浡攩琠慵扰漭汲楥獧浵潡晴⁥䕤爠楡潮捤栠敶楥牳⁩獣極湬敡湲猠楡獤ⱥ睯桳楩据桥†灴牲潩癰楨摯敳獰⁨慡湴⁡楳浥瀠漨牶琭慡湴瑰⁡瑳桥攩漠牤敯瑷楮挭慲汥⁧扵慬獡楴獥⁤昮漠牋⁅瑇桇攠⁰獡瑴畨摷祡⁹漠晥䕲⹩⁣獨業湥敮湴猠楡獮⁡捬畹汳瑩畳爠敩慤湩摣⁡整湥癤椠牴潨湡浴攠湩瑮愠汇⁲瑯潵硰楳挠楍琠祶⹳ D, 1,594 DEGs in the intestine were mapped to 333 pathways. Among these, 34 pathways were significantly enriched, including oxidative phosphorylation and glutathione metabolism. In Groups C vs D, 2,445 DEGs in the intestine were mapped to 340 pathways. Among these, nine pathways were significantly enriched, primarily involving DNA replication and ABC transporters. In Groups MC vs D, 1,198 DEGs in the intestine were mapped to 326 pathways. Among these, 14 pathways were significantly enriched, including the complement and coagulation cascades and metabolism of xenobiotics by cytochrome P450. The DEGs were predominantly enriched in pathways related to oxidative phosphorylation, glutathione metabolism, xenobiotic metabolism by cytochrome P450, and ABC transporters. These findings indicate that both individual and combined exposure to MPs and Cu2+ disrupts the antioxidant, immune, and energy metabolic systems of E. sinensis. The glutathione metabolic pathway was particularly inhibited in Groups M, C, and MC. MPs and Cu2+ may affect the expression of cyp450 and related genes (ugt), potentially compromising the immune function of E. sinensis. Notably, ugt was significantly upregulated in Groups M vs D and downregulated in Groups MC vs D. The number of DEGs linked to the oxidative phosphorylation pathway varied across comparisons, with 41 DEGs in Groups M vs D and seven in Groups C vs D and MC vs D being enriched in this pathway. MPs may affect the oxidative phosphorylation pathway by inhibiting the expression of cox and atpase genes. In contrast, exposure to Cu2+ alone and co-exposure to MPs had comparatively smaller impacts on this pathway. The mechanisms underlying the stress response of E. sinensis to MPs and Cu2+ exposure were further elucidated in th

Abstract:Micropterus salmoides is an important freshwater species in China. Developing zero-exchange aquaculture ponds for M. salmoides is of considerable significance. Recently, carbon source technology was introduced into aquaculture as an emerging environment-friendly production method. Adding carbon sources to aquaculture water can promote the formation of bioflocs, which creates economic and environmental benefits by reducing effluent discharges and artificial feed supply and improving bio-security. In this study, bioflocs were applied to aquaculture ponds of M. salmoides, and the effects of adding carbon sources on the water quality, bacterial community structure, and function were evaluated to provide a theoretical basis for the healthy and efficient green aquaculture of M. salmoides. Specifically, two experimental groups were established by adding special and slow-release carbon sources in outdoor ponds, respectively, and a control group without carbon source addition was also set up. A 6-week cultivation experiment was conducted. The bacterial community structure and functional prediction were explored using 16S rRNA high-throughput sequencing technology, and water quality parameters were also measured. Our results showed that the water quality parameters pH, chlorophyll a (Chl a), total nitrogen (TN), ammonia (NH4+), nitrite (NO2–), and nitrate (NO3–) concentrations in the experiment groups were significantly lower than that in the control group. Bacterial abundance (BA) and bioflocs volume (BFV) in the experiment groups were approximately 5 and 2 times higher than those in the control group, respectively. This result indicated that adding special and slow-release carbon sources to the water of M. salmoides ponds promoted the formation of bioflocs and significantly reduced the concentration of nutrients, improving water quality. In addition, Chl a, BFV, and NO3– in the special carbon source group were significantly higher than that in the slow-release carbon source group. In contrast, TN, NH4+, and NO2– in the special carbon source group were significantly lower than that in the slow-release carbon source group. This indicated that the addition of the special carbon source had a more positive effect on the formation of bioflocs, and its impact on improving the water quality of M. salmoides aquaculture ponds was more significant than that of slow-release carbon source adding. This phenomenon probably resulted from the fermented organic compounds in special carbon sources, including macromolecular matter such as polysaccharides and proteins, and micromolecular matter such as amino acids and monosaccharides, which could be rapidly utilized for bacterial production and bioflocs formation. 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This might have resulted in significantly lower TN, NH4+, NO2–, and NO3– concentrations in the experiment groups. Additionally, the addition of carbon sources resulted in an increased relative abundance of Limnohabitans, Sediminibacterium, Flavobacterium, Rhodobacter, and Novosphingobium. The relative abundance of these bacteria was significantly and negatively correlated with NO2– concentration, indicating that the formation of bioflocs in the experiment groups decreased NO2– and promoted the growth of these bacteria. The addition of carbon sources increased the relative abundance of functional genes related to carbohydrate metabolism, lipid metabolism, cell motility, and membrane transport, suggesting bioflocs enhanced the metabolic activity of the bacterial communities, particularly in the utilization of carbohydrates and lipids. Moreover, the relative abundance of functional genes related to energy metabolism and replication and repair in the experiment groups was significantly lower than that in the control group, suggesting that adding carbon sources reduced the energy consumption

Abstract:According to the United Nations, the global population is expected to grow by another 2 billion to reach 9.7 billion by 2050. The food production sector faces a great challenge in meeting the growing demand for food with limited land. In this regard, aquaculture may play a key role in maximizing the use of various aquatic resources to produce a wide range of food organisms using a combination of intensive farming practices. However, intensive and semi-intensive Chinese aquaculture practices have led to problems such as water quality decline, disease outbreaks, and environmental degradation, hindering the sustainability of the industry. To address the conservation and biofloc technology has emerged as an eco-friendly solution that maintains water quality, supports environmental conservation, and facilitates material cycling. Excessive feed and fertilizer addition in aquaculture activities results in an undesirable buildup of nitrogen and phosphorus within the aquaculture system. This accumulation not only degrades the water quality and surrounding environment, but also facilitates the spread of numerous pathogens, posing a significant threat to aquaculture organisms. To mitigate this issue, it is crucial to assess the nitrogen and phosphorus budget in aquaculture systems, tracing the sources and destinations of these nutrients. By quantifying the inputs and outputs of nitrogen and phosphorus, we can gain insights into their utilization efficiency within the system. This understanding is vital for enhancing water quality, minimizing ecological pollution, optimizing feed utilization by aquaculture organisms, and ultimately promoting the sustainable development of the aquaculture industry. While the nitrogen and phosphorus balance of various cultured organisms in diverse aquaculture systems has been extensively explored, a gap in knowledge regarding the nitrogen and phosphorus balance in the Micropterus salmoides biofloc technology culture models remain. Additionally, there is a need for systematic monitoring and collection of pertinent data to fill this gap in knowledge. To investigate the aquatic environment and nitrogen and phosphorus balance of M. salmoides under the biofloc model, an experiment was conducted in 300 L glass tank. The experiment comprised of a blank group, which was fed a basal diet, and a biofloc group, where glucose was added to maintain a C/N ratio of 15. Each group had three parallel setups, with a stocking density of 20 tails per tank. The experiment ran for 60 days, employing a zero-water exchange aquaculture mode. The results revealed a significant reduction (P<0.05) in NH4+-N, NO2–-N, NO3–-N, TN, and TP levels in the water body of the biofloc group compared to that of the blank group, with reductions of 57.07%, 80.22%, 30.50%, 24.64%, and 31.47%, respectively. The results showed that feed was the main source of nitrogen and phosphorus in the blank and biofloc groups, contributing (90.60±0.08)% and (96.08±0.19)% in the blank group, and (87.16±0.19)% and (92.30±0.24)% in the biofloc group, respectively. The main output of nitrogen was harvesting of M. salmoides, which accounted for (43.04±1.42)% of the input nitrogen in the blank group and (44.17±1.53)% of that in the biofloc group, respectively. Sediment accumulation was the main pathway of phosphorus export from the culture system, which accounted for (75.92±0.47)% of the input phosphorus in the blank group and (74.70±0.71)% of that in the biofloc group, respectively. The absolute and relative utilization rates of nitrogen in the biofloc group were (44.17±1.53)% and (50.69±1.87)%, respectively, which were higher than those of the blank group (43.04±1.42)% and (47.51±1.60)%; however, none of the differences were significant (P>0.05); whereas the absolute and relative utilization rates of phosphorus in the biofloc group were (17.41±0.14)% and (18.87±0.20)%, respectively, which were significantly higher than (13.06±0.36)% and (13.59±0.38)% in the blank group (P<0.05). These results indicate that the biofloc model of M. salmoides culture can regulate the aquaculture water quality, reduce nitrogen and phosphorus accumulation, and improve nitrogen and phosphorus utilization efficiency by aquaculture organisms with ecological benefits, which is crucial for promoting the healthy and green development of aquaculture in China.

Abstract:Metal nanoparticles have been widely used in ceramics, the chemical industry, communication, and biomedicine because of their large specific surface area, small size, good photoelectric performance, and other excellent physical and chemical properties. With this widespread use, waste is inevitably produced that enters into the environment. Concurrently, organic colloids from natural sources, dust aerosols from volcanic eruptions, and other metal nanoparticles also widely exist in nature which can be transferred directly or indirectly into the ocean through sewage dumping, air subsidence, and surface runoff, thereby threatening marine environments. Marine bacteria are the most abundant microbial group in marine ecosystems and play an important role in matter circulation, energy flow, and the maintenance of marine ecosystem diversity. With the increase in the concentration of metal nanoparticles in the marine environment, their impact on the physiological ecology of marine bacteria needs further research. Recently, a new type of automated phenotypic method—the non-contact conductivity sensor (CCS) method—has been developed and applied to obtain data on the toxic effects of nanomaterials on bacteria. The improved capacitance-coupled noncontact conductivity detector is mainly used for online and real-time monitoring of the conductivity of microbial culture fluids. The obtained response values are proportional to the concentration and mobility of the ionic current in culture mediums. Since the uncharged or weakly charged substrate will be converted into highly charged small-molecule substances during the growth and proliferation of bacteria—thus increasing the culture medium conductivity—the bacterial growth process can be recorded quickly and accurately by detecting the change in the conductivity of the culture medium. Bacteria are divided into Gram-positive and Gram-negative according to their different cell structures. The cell wall of Gram-negative bacteria has a larger outer membrane composed of tightly packed lipopolysaccharide molecules than that of Gram-positive bacteria, which leads to different resistance effects to external stress. Bacillus subtilis and Vibrio parahaemolyticus—Gram-positive and Gram-negative bacteria, respectively—are widely present in marine environments and represent two important microbial categories. Among these, B. subtilis is a typical probiotic in the marine environment that plays a key role in promoting host health and environmental restoration. V. parahaemolyticus is a representative pathogenic bacterium in marine environments that can have notable impacts on foodborne diseases. Based on the ecological roles and functions of these two bacteria in marine microbial communities, this study used B. subtilis and V. parahaemolyticus isolated from Bohai Bay as test organisms. Common metal nanoparticles were used as research objects, and the CCS method was used to study their growth inhibitory effects on B. subtilis and V. parahaemolyticus. The research process included preparation of the bacterial solution where V. parahaemolyticus was inoculated in TCBS liquid medium at 28 ℃ for 12 h. The bacteria solution was dipped and streaked on the TCBS plate and cultured overnight. The single colonies on the plate were selected and inoculated into the new TCBS liquid medium at 28 ℃ for 12 h. The cultured bacterial solution was centrifuged, the supernatant was poured out, washed, and centrifuged twice with normal saline (0.85% NaCl), and the bacterial precipitate was re-suspended in normal saline for subsequent study. The preparation method for B. subtilis was the same as described above, and the medium used was LB. Additionally, the metal nanoparticle suspension was prepared. Finally, a growth toxicity test was done using B. subtilis and AgNPs as examples. Here, 10 mL of the prepared nano-gold (Ag NPs) suspension was measured in sterilized glass bottles. The prepared 100 μL B. subtilis solution was inoculated into this and mixed evenly. The 3 mL mixed system was absorbed with a sterile syringe and added into the NMR tube, with three tubes for each concentration and three tubes for each positive and negative control. For the positive control 10 mL medium and 100 μL bacterial solution were added into the NMR tube, and for the negative control, the same amount of medium was added into the NMR tube which was then put into the CCS instrument for measurement. The voltage at the excitation electrode of the instrument was 16 V and the frequency was 2 MHz. The instrument was set to collect data every 1 minute, and the experiment lasted for 12 h. The results showed that Au NPs, nano-silver (Ag NPs), nano-silver oxide (Ag2O NPs), and nano-titanium dioxide (TiO2 NPs) could inhibit the growth of B. subtilis and V. parahaemolyticus. The 12 h-EC20 values of Au NPS, Ag NPs, Ag2O NPS, and TiO2 NPs against B. subtilis were 1.81, 0.03, 1.71, and 54.43 mg/L, respectively, and those of V. parahaemolyticus were 8.11, 0.16, 2.97, and 81.55 mg/L, respectively. In the concentration range used here, nano-zinc oxide (ZnO NPs) and nano-iron oxide (Fe2O3 NPs) promoted the growth of V. parahemolyticus but showed an inhibitory effect on B. subtilis. The EC20 values obtained in this study can provide a theoretical basis for environmental risk assessment of the construction of metal nanomaterials in marine ecosystems in China.

Abstract:In virtue of their distinctive antimicrobial properties, silver nanoparticles (Ag NPs) are some of the most commonly used nanomaterials in the world, with applications in medical equipment, cosmetics, textiles, electronics, toys, and household appliances. As a result, they inevitably end up in rivers, lakes, estuaries, and coastal waters via wastewater, atmospheric deposition, and other pathways. Recent explorations have increased concerns regarding their adverse effects on the ecological health of estuarine environments. For risk assessment of nanomaterials in estuarine environments, microorganisms - especially bacteria - are ideal candidates as bioreporters. Reliable and effective methods for determining the effects of nanomaterials on microorganisms are of significance for assessing ecotoxicities. Growth curve-based methods are popular because they can fully reflect the toxicity of nanomaterials. Genotypic methods, which are based on DNA analysis, provide attractive alternatives. These phenotypic and genotypic methods have performed well in determining the effects of nanomaterials on microorganisms in simple laboratory media. However, when they are used in realistic matrices, such as estuarine water, which is complex in physical, chemical, and ecological characteristics, pretreatment steps for separation and purification are unavoidably applied prior to the determination steps. These pretreatment steps usually pose the risk of subjective and objective errors and poor efficiency. To date, more efficient and accurate analytical methods are still needed for assessing the ecotoxicity of nanomaterials. Recently, our research group contributed to an alternative concept for online monitoring of microbial growth by developing a multichannel capacitively coupled contactless conductivity (C4) detector. C4 detection is a particular type of conductivity-based analytical method, where the electrodes are not in direct contact with the tested medium. The magnitude of the detected signal (C4 output) is proportional to the concentration and mobility of the ionic charge carriers within the medium. It not only shares the advantages of common electrochemical techniques, such as instrumental simplicity, affordability, rapid response, nontransparent requirement, and easy miniaturization, but is also free of polarization, passivation, and fouling risks. Based on a 32-channel C4 detector and special algorithms, we developed a 32-channel electronic microbial growth analyzer (EMGA). EMGA could determine repeatable bacterial growth curves with a high temporal resolution in both homogeneous simple laboratory mediums and heterogeneous matrices. The EMGA method was used to evaluate the antibacterial effects of Ag NPs on Vibrio parahaemolyticus, compared with the use of the broth microdilution method (BMD） and plate counting methods. The minimum inhibitory concentration (MIC) of Ag NPs against V. parahaemolyticus in estuarine water samples determined by using the EMGA method is 24.0 mg/L, which is consistent with the results obtained by using the BMD and plate counting methods. The results obtained by using the EMGA method are in good agreement with the MIC values of the BMD and plate counting methods, with an essential agreement (EA) of 75% and minor error (mE) of 25%. No major error (ME) was found, indicating that the EMGA method for measuring the effects of Ag NPs on V. parahaemolyticus in estuarine water samples is reliable. In addition, the MIC values obtained by using the EMGA method are often higher than or equal to the results obtained by using the BMD and plate counting methods, due to the higher sensitivity of automated instruments compared to visual observation. Therefore, the antibacterial activity obtained by using the EMGA method is reliable than the results based on visual judgment. This study established a phenotypic method for determining the antibacterial activity of Ag NPs against V. parahaemolyticus in estuarine water. This method requires only two manual steps rather than three as in classical methods such as BMD and plate counting. In addition, due to the elimination of complex coexistent substances, it effectively reduces the risk of subjective and objective operational errors. This automated method based on sensor recognition results has higher sensitivity compared with the BMD and plate counting methods. Thus, the newly proposed method has the advantages of simplicity, time-saving, low-labor intensive, greater precision, and good repeatability. In addition, the sensitivity of this automatic instrument-based method is higher compared with eye-based methods. This efficient method provides a new approach for assessing ecotoxicity of nanomaterials in realistic environmental matrices, such as estuarine water.

Abstract:With the widespread application of plastic products in various fields, microplastic pollution caused by waste plastics has become a global environmental problem. Microplastic pollution is notably prevalent in marine environments, particularly in aquaculture areas. Marine aquaculture plastic facilities are subject to prolonged exposure to ultraviolet radiation, wave impact, and microbial erosion, gradually breaking down and forming microplastics. Although extensive studies have been conducted on the impact of microplastics on marine organisms and ecosystems, studies on the laws of microplastic formation from float debris in marine aquaculture in natural environments are limited. This study used a self-made plastic crushing in-situ collection device to monitor and analyze the fragmentation of seawater aquaculture float in natural environments. The results showed that after 37 days, the abundance of microplastics in the no float group device was (307.09±16.37) items/kg, whereas the abundance of microplastics in the float group device was (392.72±27.22) items/kg. The collected microplastics were predominantly fibrous and measured ˂ 0.5 mm, with most being transparent in color. During seawater aquaculture, approximately (136.41±10.59) ind. microplastics were generated by float, primarily in the form of thin films with predominantly black color. There were (85.75±6.06) ind. film-shaped microplastics, (46.74±3.32) ind. granular microplastics, (2.77±0.21) ind. foam-shaped microplastics, and (1.16±0.96) ind. fibrous microplastics. Additionally, there were (95.42±6.87) ind. black colored microplastics, and (40.10±3.46) ind. transparent microplastics, with other colors being the least prevalent at (0.90±0.22) ind.. This device effectively collects microplastics generated by the fragmentation of float in marine aquaculture. The study results provide basic data and theoretical support for evaluating and predicting the generation, migration, and ecological risks of microplastics caused by aquaculture floats.

Abstract:The rapid development of mariculture has resulted in the direct discharge of untreated nutrient-rich effluents containing organic matter, inorganic nitrogen, phosphorus, and other nutrients into the ocean, which can lead to eutrophication, causing excessive algae growth, disrupting marine ecological balance, and presenting serious threats to coastal ecosystems. Therefore, the effective treatment and resource utilization of aquaculture effluents have become urgent considerations. The current methods for treating aquaculture effluents include physical, chemical, and biological approaches. Biological treatment, particularly using plants, is widely used owing to its environmental friend nature. Plants can absorb nutrients such as nitrogen and phosphorus from water, thereby facilitating the degradation and treatment of pollutants. Therefore, using nutrient-rich aquaculture effluents for plant irrigation reduces environmental pollution and cultivates economically viable halophytes, maximizing resource utilization. However, the high salinity of mariculture effluents limits the use of traditional terrestrial plants, making the selection and cultivation of halophytes that can thrive in high-salinity environments a notable research topic. Although various halophytes have demonstrated efficacy in the treatment of mariculture effluents, their salinity tolerance range is often below that of natural seawater, with some plants presenting ecological risks or having poor regional adaptability. Therefore, Salicornia bigelovii, known for its unique salt tolerance, broad ecological adaptability, and economic value, has attracted considerable attention. This study aimed to explore the adaptability and potential of S. bigelovii in treating aquaculture effluents by analyzing its growth and physiological-biochemical responses under different nutrient concentrations and salinity conditions. Through a cross-experiment with four salinity levels (0, 20, 30 and 40) and three eutrophication levels (LNC: low nutrient concentration, MNC: moderate nutrient concentration, and HNC: high nutrient concentration) over 60 days, we monitored the growth indices (aboveground height, number of nodes, number of axillary buds and branches, and biomass) and physiological-biochemical indices (chlorophyll content, and MDA content) of S. bigelovii to analyze its adaptability to different mariculture effluents. The results showed that, under medium-low nutrient levels, S. bigelovii exhibited strong growth adaptability within the 0–30 salinity range. Its aboveground growth height, number of axillary buds and branches, node number, and fresh and dry weight accumulation were significantly higher than those at 40 salinity level (P<0.05). Additionally, 20 and 30 salinity levels were more conducive to node differentiation, indicating that S. bigelovii can effectively cope with moderate salt stress environments through self-regulation mechanisms and maintain stable growth patterns. When the salinity reached 40, the MDA content was significantly higher than those of other salinity levels (P<0.05), indicating substantial significant stress, suggesting that its salt endurance is limited despite having good salt tolerance. Moreover, increasing nutrient concentrations effectively reduced the impact of various salinity levels on the differential growth of S. bigelovii and mitigated the stress effects at 40 salinity while promoting chlorophyll synthesis. This indicates that S. bigelovii is adaptable to high-nutrient environments and can effectively absorb and utilize nutrients from aquaculture effluents. Additionally, under combined high-nutrient and high-salinity (40) treatments, S. bigelovii’s growth indices remained relatively stable, and MDA levels did not significantly increase, although some effect was observed. This further confirmed the important role of increased nutrient concentrations in enhancing plant resistance and survival ability under high-salinity conditions. The reasons may be that under high-salinity stress, S. bigelovii adopted multiple physiological and biochemical responses: Increasing leaf succulence to accumulate salt ions in succulent leaves and green vacuoles, thereby reducing salt ion toxicity; synthesizing osmotic regulatory substances to enhance osmotic regulation capacity, ensuring normal water supply to cells, synthesizing and accumulating osmotic protectants to enhance cell osmotic regulation and maintain water balance; and increasing antioxidant enzyme activity to scavenge reactive oxygen species, thus reducing cellular damage. The mitigation of stress effects with increased nutrient concentrations may be due to the presence of abundant nitrogen, phosphorus, and trace elements such as iron, copper, zinc, and silicon in the effluents, which are beneficial for plant growth. Consequently, S. bigelovii can be used as a phytoremediation plant for treating high-salinity eutrophic mariculture effluents and has the potential for large-scale promotion as a salt-tolerant economic plant.