Understanding the role of the Yellow Sea Bottom Cold Water Mass (≤10ºC) on the survival strategy of Euphausia pacifica throughout the hot summer in the Yellow Sea

Abstract

The Yellow Sea Bottom Cold Water Mass (YSBCM: ≤10°C) is a unique physical feature of the Yellow Sea.It forms through winter cooling and mixing and it is persistently observed in the deep central region during summer. Although the important role of YSBCM on physical and biological processes in Yellow Sea has been recognized, few studies have been conducted to understand its role. Particularly, it provides a refuge (i.e. oversummering sites) for some organisms (i.e. Euphausia pacifica) to survive through the hot summer (>20°C in surface). Therefore, various studies of E. pacifica, such as their feeding ecology, live experiments, and their spatial and seasonal distribution using net sampling with acoustics, are being conducted to better understand the role of the YSBCM on E. pacifica. According to preliminary results, high egg abundance of E. pacifica was found during the spring before the YSBCM was formed but no eggs were found in the summer. However, E. pacifica lipid content (about 10% of dry weight), which is closely linked with living strategy, was not significantly changed between seasons. Therefore, in order to fully understand E. pacifica’s over-summering strategies (e.g., migration,hibernate, shrinkage, minimizing metabolism) and the YSBCM role on E. pacifica, further analyses (acoustics, net sampling, stomach analysis, so on) are currently being done.