Abstract:In recent years, continuous high temperature and marine heat waves in summer have become major limitations for the sustainable development of sea cucumber aquaculture. In 2019, our team invented a cooling equipment based on cooled atomization air, which can reduce the water temperature of the culture pond in summer. Previous tests showed that the survival rates of the sea cucumbers in the equipped ponds were higher than the unequipped ponds during the high temperature. In this study, five equipped ponds were selected as experimental groups (groups E1 and E2 were labeled according to their geographic location) and three unequipped ponds were selected as control groups (labeled group C), then the water quality, sedimental quality, and the sedimental microbial community structure of the eight ponds were analyzed in order to reveal the mechanism of the higher survival rate using the cooling equipment. The results showed that the temperature of the bottom water of the two experimental groups was significantly lower than that of the control group (P<0.05). The dissolved oxygen (DO) level in the bottom water of the experimental groups was significantly higher than that of the control group (P<0.05). Both the ammonia nitrogen concentration in the bottom water and the concentrations of nitrite nitrogen, and chemical oxygen demand (COD) and ammonia nitrogen in pond sediments of the two experimental groups were significantly lower than that of the control group (P<0.05). The sedimental microbial community structure of all the ponds was also investigated, and the OTUs (optical transform units) were numbered from 707 to 808. Alpha diversity analysis showed that the abundance and diversity of the experimental group were higher than those of the control group. PCoA (principal coordinates analysis) showed that the bacterial composition and community structure among the two experimental groups were more similar, while there were significant differences between the experimental and the control groups. The species distribution analysis on the order level showed that the similarity between the two experimental groups is higher than that between the experimental and control groups. The relative abundance of Rhizobiales, Lactobacillales, and Micrococcineae in the experimental groups were significantly higher than that in the control groups. Thirteen OTUs with significant differences among three groups were selected using LEfSe (LDA effect size) analysis. The correlation analysis between microbial community structure and environmental factors showed that the abundance of microbial species involved in the nitrogen cycle was significantly higher in the experimental groups than that of the control groups. Then OTU7, OTU29 and OTU108 were screened and significant correlation was found with ammonia nitrogen concentration in all of the tested ponds, and they are classified as Ochrobactrum, Escherichia-Shigella and Bacillus, respectively. In the 25 predicted COG (clusters of orthologous groups of proteins) metabolic pathways in prokaryotes, 18 metabolic pathways exhibited significant differences (P <0.05) between the experimental groups and the control groups. All the results indicated that the use of the equipment could significantly improve the pond water quality and sediment environment, and positively affect the sedimental microbial community structure of the bottom water. The results of this study would provide scientific support for the popularization and application of the equipment.
