Potential shift in mesozooplankton community structure in response to climate-driven changes during summer in the Ulleung basin

Abstract

The sea surface temperature exhibited increasing trend over the last decade during the summertime in the Ulleung basin. The community of mesozooplankton may be used as indicator of climate change due to their rapid response to changing environment. This study aims to characterize mesozooplankton community composition in relation to the climate-driven physical features in the Ulleung basin of the East Sea/Japan Sea during the summer of 2009-2020. The SST ranged 19.3-28.0°C (mean: 25.1°C) and risen by 0.7°C in 2020 compared to 2009. SST anomalies had two negative (2009–2011 and 2014) and two positive (2012–2013 and 2015-2020) phases. The surface chlorophyll-a (chl-a) concentrations showed slightly increasing trend and highly positive anomaly in 2020. The average abundance of mesozooplankton ranged 2,906–40,558 inds.m-3 (mean: 10,129 inds.m-3) and showed slightly increasing long-term trend (r2 =0.31, p<0.1). The cluster analysis was carried out to identify the mesozooplankton community that contributed to the changes in long-term community structure. The community that contributed to the increasing trend were distinctive, in which Noctiluca scintillans contributed to the increasing trend in 2009, 2012–2015 and 2017, and immature copepods contributed to higher abundance during 2010–2011 and 2018, and abundance of Pyrocystis noctiluca contributed to rapid increase of mesozooplankton abundance in 2020. Our results suggest that gradually increasing abundance of N. scintillans and P. noctiluca are probably related to the increasing trends of SST and chl-a concentrations, and that there may be shifts in the community structure in the future.