Shrimp community structure and its relationship with environmental factors in the offshore waters of Zhoushan Islands

Abstract

In order to learn about the condition of shrimp resources in the waters outside Zhoushan Islands, the relationship between shrimp species composition, dominant species, biodiversity, community structure characteristics and environmental factors was analyzed in April (spring) and October (autumn), 2018. The research indicates that:firstly, there are 32 varieties of shrimp in outer waters of Zhoushan Islands, belonging to 10 subjects, 21 genera, 22 species in spring and 29 kinds in autumn. Compared with historical survey results, the number of shrimp species in this sea area has decreased and the trend has slowed down. Secondly, the dominant species changes significantly, with the spring dominant species being <italic>Metapenaeopsis dalei</italic> and <italic>Metapenaeopsis barbata</italic>, which are mainly inhabited in the southeastern sea of the survey area, and the autumn dominant species is <italic>Parapenaeopsis hardwickii</italic> and <italic>Solenocera crassicornis,</italic> which are mainly found in the north and southwest of the survey area. Thirdly, both Shrimp Richness Index (<italic>D</italic>) and diversity index (<italic>H'</italic>) in spring are lower than those in autumn, while uniformity index (<italic>J'</italic>) value in spring is greater than that in autumn. Shrimp is the most abundant in the water depth of 60-70 meters and the uniformity index (<italic>J'</italic>) value is the highest in the water depth zone from seventy to ninety meters. That’s because spring is the breeding season for most shrimps, shrimp mainly spawning grounds and habitats in the near shore waters, when the richness and species diversity of the outer waters are low, and in autumn, with the weakening of Taiwan’s warm currents resulting in a decrease in warm waters, some shrimp species are in the deep waters of the sea that contribute to the richness of species in autumn. In spring, there is more shrimp in this field with better uniformity, and the autumn shrimp in the sea is mostly adults. The hydrologic environment has less influence on it, so the uniformity is lower than that in the bottom. Fourthly, according to cluster analysis and non-measured multi-dimensional scale sequencing analysis, spring at 45 percent of the similar level is divided into 4 communities, while autumn at 60 percent of the similar level is divided into 3 communities. The similarity between the sea communities is lower than the degree of similarity, and the similarity of autumn shrimp communities is higher than that in spring, indicating that the similarity of autumn shrimp species in the waters outside the Zhoushan Islands is higher than that in spring. Spring in the biological volume and species level are lower than those in autumn. The average similarity in the spring group is lower than that in autumn, and the characteristics with the highest similarity contribution rate in the spring and autumn groups are Dai's prawns and Haas imitation prawns, and the inter-group sex of the two seasons is as high as 82.36%, which may be because in the spring and autumn shrimp catches, individual species has a larger amount of each season or a significant advantage in their respective seasons. SIMPER analysis shows that the shrimp with the highest similarity contribution rate in the spring and autumn groups is consistent with the species of each dominant species. The ANOSIM test demonstrates the shrimp community structure is significantly different in the two seasons. fifthly, CCA analysis makes it clear that temperature is one of the main environmental factors affecting the distribution of shrimp in this area. In autumn, the high temperature high saline system impacted by Taiwan's warm currents becomes the main water group factor in the survey area, and the salinity is regulated by the physiological activities of shrimp, such as shrimp metabolism and osmosis pressure regulation, thus influencing the structure of the shrimp community. Salinity only has a significant effect on the structure of shrimp communities in autumn.