Upwelling as a nursery for fish larvae: Summer observations from the Taiwan Bank

Abstract

The present study investigated the impact of upwelling on the hydrographic conditions and fish larvae assemblages around the Taiwan Bank. In July 2023, a total of 2061 fish larvae were collected, representing 130 species from 61 families and 99 genera, identified through DNA barcoding. The dominant taxa included Bleekeria mitsukurii, Lactarius lactarius, Sillago ingenuua, Encrasicholina heteroloba, and Selaroides leptolepis. At central region of the bank, a low-temperature, high-salinity water mass extended toward the surface, delineating the principal upwelling zone. Within this region, elevated fluorescence and zooplankton abundance created favorable breeding conditions for fish larvae. Cluster analysis revealed two distinct summer assemblage groups: (i) stations in the northern non-upwelling area and the central upwelling zone, and (ii) stations in the southern bank. Assemblages in the southern group were compositionally distinct from those in both the northern and central regions, largely due to the presence of mesopelagic larvae transported northward by the South China Sea Surface Current. We propose that the upwelling waters act as a barrier, limiting further northward dispersal of these mesopelagic larvae into the upwelling zone and adjacent shallow habitats.