Impact of the warm eddy on planktonic ciliate, with an emphasis on tintinnids as bioindicator species

Abstract

Mesoscale eddies are a common feature of world oceans. However, their influence on microzooplankton has not been well studied. This study investigated the impact of warm eddies (originating from the Kuroshio Current) on planktonic ciliates in the northern South China Sea and the western North Pacific. We found more tintinnid species in warm eddies than in reference areas in both seas. All species categorized as abundant (maximum abundance > 5 ind. L−1 and occurrence frequency > 10%) could be divided into subsurface-peak and surface-peak groups (highest abundance appeared in subsurface and surface layers, respectively). Subsurface-peak tintinnid species vertical distribution together with temperature-salinity-plankton diagrams at each sampling points revealed higher abundance in warm eddies than in reference areas, which suggested that they can act as warm eddy bioindicator species. Surface-peak tintinnid species were mainly distributed in both warm eddy and reference areas, depth and temperature were the main influence factors. The vertical distribution in warm eddies showed a bimodal pattern in both the South China Sea and North Pacific, with abundance peaks in surface and subsurface layers; whereas in reference areas, abundance peaks in surface layers. The average abundance of ciliate and tintinnids in subsurface layers were higher in warm eddies than in reference areas. Our study contributed to a better understanding of the impact of the warm eddy on microzooplankton and tintinnids function as usefully bioindicator species. Further research is needed to fully understand the ecological influence of eddies on the microzooplankton community.