Synergistic impacts of environmental drivers on mesozooplankton community composition in the Ulleung Basin: A decadal analysis

Abstract

The mesozooplankton community may be used as an indicator of climate change due to their rapid response to changing environment. The sea surface temperature exhibited an increasing trend over the last decade during the summertime in the Ulleung basin, East/Japan Sea. The structural changes of mesozooplankton community in relation to the climate-driven factors in the surface mixed layers of Ulleung basin were investigated during the summers of 2009- 2022. The anomalies of foraminiferans, Pyrocystis noctiluca, and larvae of macrobenthos showed a significantly increasing long-term trend (p < 0.1) whereas Noctiluca scintillans, chaetognaths, and ostracods showed a slightly increasing long-term trend. The mesozooplankton showed a slightly increasing long-term trend with peaks in 2015 and 2020. The two peaks of mesozooplankton abundance were mainly due to the dominance of N. scintillans, and the common feature was the close passage and meandering of East Korea Warm Current (EKWC). The next dominant taxa were thaliaceans and P. noctiluca in 2015 and 2020, respectively. The volume of Tsushima warm current in the western channel (v-west) was 1.3 times greater in 2020 compared to 2015, and the occurrence of marine heatwave was detected in 2020 while not detected in 2015. The peaks of mesozooplankton were due to the meanders of EKWC, however, the strong v-west together with the occurrence of MHW may have transported a high abundance of subtropical species P. noctiluca and allowed its persistence during 2020. Thus, the climate-driven factors may have a synergistic influence on the long-term changes in mesozooplankton community composition