Niches of four large crustacean species in Laizhou Bay

Niche theory explains mechanisms of interspecific coexistence and competition in communities. Chinese shrimp (Fenneropenaeus chinensis), swimming crab (Portunus trituberculatus), Japanese stone crab (Charybdis japonica), and Japanese mantis shrimp (Oratosquilla oratoria) are all large-bodied commercially exploited crustacean species in Laizhou Bay, China, with similar food habits. Populations of two of these species, F. chinensis and P. trituberculatus, are also regionally enhanced. Study of the community status, interspecific associations, and spatial niche characteristics of these four crustacean species is warranted to guide stock enhancement and fishing quota management. Data for analysis of community status and spatial niche were collected by bottom-trawl surveys at 20 stations in summer from 2010 to 2019. Representative samples of these four crustacean species, and their potential food sources were collected in 2010, 2011, 2018 and 2019. Using stable carbon and nitrogen isotopes we analyze trophic levels, nutritional niches, and diets of these crustaceans. Average F. chinensis biomass (51.0 g/h) was lowest, followed by P. trituberculatus (107.0 g/h). In most years, O. oratoria and C. japonica were most dominant, and F. chinensis and P. trituberculatus were typically important species in the community. Associations between these four species are not strong, with a significant positive association occurring mainly between F. chinensis and the other three species. The niche width of C. japonica is greatest (2.45), followed by O. oratoria (2.13), F. chinensis (1.92), and P. trituberculatus (1.93). A high niche overlap is apparent between F. chinensis and the other three species; trophic levels of each are similar, ranging 3.02-3.28. The total niche area of F. chinensis is the greatest, while that of P. trituberculatus is similar to those of C. japonica and O. oratoria. Nutritional niche overlaps between P. trituberculatus and C. japonica are relatively high. Proportionally more bivalves are ingested by F. chinensis than any of the other species, for which diets are more homogeneous. Although populations of P. trituberculatus and F. chinensis have expanded through enhancement, the crustacean community structure in Laizhou Bay has not changed greatly. On the basis of community status, inter-species connectivity, spatial niche width and overlap, trophic level and nutritional niche, and the diets of these four crustaceans, F. chinensis is least competitive with other taxa, and P. trituberculatus is more competitive with C. japonica and O. oratoria. To maximize benefits of regional crustacean enhancement, we suggest consideration be given to competition between species, and niche similarities, to determine appropriate release sites and quantities.