Population characteristics of the dominant cold-water brittle star Ophiura sarsii vadicola (Ophiurida, Ophiuroidea) in the Yellow Sea

Global warming has severe effects on cold-water habitats. The Yellow Sea Cold Water Mass (YSCWM) is a typical cold-water habitat in the western Pacific Ocean. The southern YSCWM face much more environmental pressure than the northern YSCWM. We hypothesize that the cold-water Ophiuroid species Ophiura sarsii vadicola, the dominant benthic species in the YSCWM, will be less abundant with an ageing population in the northern YSCWM. Based on a survey in 2018, we found the density of O. sarsii vadicola reached 315 inds./m2 in the northern Yellow Sea, higher than previous records. Biomass and organic mass peaked at 45.5 g/m2 and 4.89 g/m2. There was a strong linear relationship between wet weight and dry weight/ash-free dry weight (AFDW). Over 48 000 individuals were measured (diameter: 1.0-17.5 mm) and were notably smaller than related species from higher latitudes. A Gompertz growth model was established by examining ossicle growth bands. Age structures differed between the northern and southern YSCWM, and the former was dominated by younger individuals. This study enriched our understanding on the ecology of brittle star and provides valuable data and insights for future research on the benthic ecosystems of the Yellow Sea.