Study on the annual variation of crab species diversity in spring in the waters near Zhongjieshan Islands, Zhejiang Province

Objective This study aims to examine the interannual variation in the species diversity of crabs in the waters around Zhongjieshan Islands, Zhejiang Province during spring.

Methods Based on the bottom trawl fishery resource survey data in spring (April) from 2016 to 2020, the abundance density index, relative importance index, biodiversity index, species turnover rate, abundance density contribution rate, and redundancy analysis method (RDA) were applied to study the species composition, species turnover, dominant species, abundance density status, community stability, contribution of dominant species to the abundance density of crabs during spring, and their relationships with environmental factors, respectively.

Results The study showed that a total of 14 species of crabs, belonging to 1 order, 6 families and 9 genera, were caught in spring over the five years, among which, 8 species were caught in 2016, 6 species were caught in 2017, 10 species were caught in 2018, and 9 species were caught in each of 2019 and 2020. The turnover rate of the number of species between the adjacent years ranged from 36.36% to 44.44%. Both biomass and number density were the highest in 2018, with the lowest biomass occurring in 2016 and the lowest number density in 2019. Portunus trituberculatus, Charybdis japonica and C. bimaculata were all co-dominant species over the five years, in which the total contribution of P. trituberculatus and C. japonica to crab biomass was more than 54% in each year. The richness and evenness were both the highest in 2018, while the highest diversity occurs in 2019, and both diversity and evenness were the lowest in 2017, while the richness was the lowest in 2020. The abundance of P. trituberculatus and C. japonica showed a significant positive correlation with dissolved oxygen (DO) at the bottom of seawater (P<0.05), and a significant negative correlation with water depth and bottom seawater salinity (P<0.05), while the abundance of C. bimaculata showed a significant positive correlation with bottom seawater temperature (P<0.05).

Conclusion The crabs community in the waters around the Zhongjieshan Islands in spring of 2016—2020 was lightly disturbed.