Abstract:Inshore islands are one of the most representative marine areas responsible for a significant part of the oceanic primary productivity. The most representative archipelago in northern China, the Miaodao Archipelago, is located at the confluence of the Yellow Sea and Bohai Sea. It is an important habitat and migration channel for marine life and is a hot spot for biodiversity research. However, the increasing exploitation of marine natural resources in the waters adjacent to inshore islands, such as mariculture, fishing, shipping, and energy exploitation, is putting increasing pressure on marine life. These factors have resulted in marine community disturbance to varying degrees and pose a severe challenge to biodiversity conservation. Due to human activities and climate changes, the Miaodao Archipelago biodiversity has been affected to some extent. Nonetheless, only few investigations have been performed on the bottom fisheries in this area. With the establishment of the Changdao National Wetland Nature Reserve, it is urgent to conduct systematic biodiversity research in this sea area to promote the restoration and protection of marine biodiversity. To systematically understand the diversity distribution characteristics of bottom fishery communities in the Miaodao Archipelago adjacent sea, a single-ship trawl survey was conducted monthly in September, November, and December 2020 and from March to December 2021. Based on the richness index (D), evenness index (J´), biodiversity index (H´), redundancy analysis (RDA), and abundance-biomass comparison (ABC) curves the bottom-fishery biodiversity and its influencing factors were analyzed to provide a scientific basis for biodiversity conservation in the Miaodao Archipelago adjacent sea. It provides basic data and data support for exploring the intrinsic, environmental, and human factors affecting biodiversity in typical islands. A total of 115 species were identified in the sampling survey, including 49 species of fish, 29 mollusks, 28 crustaceans, 8 echinoderms, and one species of brachiopods. The fish are mainly Pennahia argentata, Gobiidae, and other fish. Crustaceans are mainly Oratosquilla oratoria, Alpheus japonicus, and other crustaceans. The bottom fishery communities in the Miaodao Archipelago adjacent sea were primarily composed of Gobiidae, A. japonicus, Echinodermata, and Mollusca. The dominant species composition was different in distinct months. The dominant species were Chaemrichthys stigmatias, P. argentata, Palaemon gravieri, Trachypenaeus curvirostris, O. oratoria, A. japonicus, Charybdis bimaculata, Diogenes edwardsii, Octopus ocellatus, Glossaulax didyma, Rapana venosa, Temnopleurus hardwickii, Asterina pectinifera, Ophiothrix marenzelleri. From March to June, the bottom fishery community was mainly concentrated in the southeast area of the Miaodao Archipelago but changed to the southwest area in July and August. There was no apparent regional distribution in the rest of the months. This may be because, in colder March and April, the warmer seawater brought by the Yellow Sea Warm Current provided a more suitable living environment for the bottom fishery communities, which resulted in more communities gathering in the north Yellow Sea area southeast of the Miaodao Archipelago. In May and June, many migratory marine organisms migrated from the North Yellow Sea to the Bohai Strait, possibly resulting in high biodiversity in the southeast area of the Archipelago during this period. Many migratory organisms had arrived in the Laizhou Bay by July and August. With the increase of phytoplankton along the coast of the Laizhou Bay during summer, many consumer communities are attracted. In addition, the annual water and sediment transfer from the Yellow River in June-July may result in the introduction of large flows of fresh water and nutrients into the waters southwest of the Miaodao Archipelago, resulting in higher summer biomass in this region. The summer and autumn months showed higher biodiversity, while winter showed a single feature with higher abundance and biomass. There was a significant negative correlation between biomass and abundance of P. argentata and A. japonicus. The A. japonicus biomass and abundance may depend on the abundance of its predator, P. argentata. Other species with significant positive correlations may be jointly affected by environmental factors such as temperature. The main taxa and environmental factors RDA showed that water depth and temperature were the main environmental factors affecting the bottom fishery community structure, among which echinoderms and Terebratella coreanica were found in higher amounts. A. japonicus and temperature negatively correlated, while most other species positively correlated with temperature. The ABC curves indicated that the bottom fishery community structure was disturbed to a high degree as a whole, with only some seasons showing moderate disturbance, such as May and June 2021. Since implementing the summer fishing ban in May, the bottom fishery community structure disturbance level in the Miaodao Archipelago has decreased. The off-fishing season effectively protects the young fish of fishery species and dramatically reduces the fishing of other by-catch species, effectively recovering the fishery resources. In addition, from April to May every year, many migratory species began to migrate to the Bohai Sea through the Miaodao Archipelago, providing conditions for the increase of fishery species in this area. However, due to the large area of artificial breeding in the Miaodao Archipelago and the influence of ships navigating between the islands, the sea area experiences a significant degree of disturbance and is in an unstable state. This study provides a scientific foundation for biodiversity protection in the Miaodao Archipelago, exploring the intrinsic, environmental, and human factors affecting typical island biodiversity. However, the formation and evolution mechanisms of biological diversity in typical archipelago ecosystem still need to be explored in long-term and in-depth studies.
