Northward shift of Pacific copepods into the Chukchi Sea during summer: Implications of the Bering Summer Water (BSW) temperature

Abstract

The Chukchi Sea is the only gateway to the Arctic Ocean from the Pacific Ocean and is a major route to the influx of Pacific zooplankton. The recent oceanographic changes, such as rising water temperatures and shifting sea ice cover, have resulted in sub-polarization of zooplankton communities from the Arctic boundary. We collected zooplankton at 14 stations in the Chukchi Sea in 2015 and 2016. In addition, the mooring systems installed at the entrance of the Chukchi Sea were analyzed to obtain water temperature and salinity data for the corresponding period. As a result, the abundance of Pacific copepod species (Eucalanus bungii, Metrida pacifica, and Neocalanus spp) was high in 2015, and water temperature and salinity were also high. On the other hand, Pacific species were rarely found in 2016, and water temperature and salinity were relatively low. To further demonstrate, we have also reviewed the past 2007 and 2012 zooplankton data and temperature and salinity data of the mooring systems. And, we found a very similar result to our data in which the abundance of Pacific species was proportional to the temperature of the water entering the Chukchi Sea. In conclusion, the Pacific species introduced into the Chukchi Sea are known to flow along the Bering Summer Water (BSW), but the Pacific species show high abundance only in the relatively high temperature (> 3 °C) of the BSW.