Spatial characteristics of Salpa fusiformis in the surface waters of the western East/Japan Sea

Abstract

In order to understand the distribution characteristics of solitary blastozooid form of Salpa fusiformis with increasing frequency of occurrence, we investigated spatial heterogeneity of near-surface zooplankton using a Manta trawl (mesh size of 330 μm) and the related environmental factors on board R/V Eardo in the western East/Japan Sea from July to August in 2019. S. fusiformis distributed evenly along the center from south to north in the study area. S. fusiformis with size classes of 0.33-1mm, 1-2mm and 2-5mm showed relatively high abundances in the southern part, whereas the plankton >5mm peaked in the southern and northernmost stations of the study area. Log-transformed abundances of the plankton (0.33 1mm, 1-2mm and 2-5mm) showed significant correlation with environmental factors and 16 neustonic zooplankton taxa (330μm-1mm), especially salinity (p<0.05) and fish larvae (p<0.01). Except plankton >5mm, S. fusiformis of the other 3 size classes was negatively correlated with salinity, indicating that the high abundances were existing in the less saline waters. On the other hand, the plankton in the range of 5.75-88.50 mm (ave. 21.68mm) was likely associated directly with the currents rather than other environmental factors. And, S. fusiformis of all size classes was not significantly correlated with the most neustonic zooplankton groups except fish larvae, indicating that the widespread S. fusiformis did not affect most taxa in the near-surface zooplankton during the study. Our results suggest that S. fusiformis showed range expansion at seas around Korea associated with currents and salinity during the study considering the previous studies.