Mass Occurrence of Pacific Copepods in the Southern Chukchi Sea During Summer: Implications of the High-Temperature Bering Summer Water

Jee-Hoon Kim,Sung-Ho Kang,Kyoung-Ho Cho,Won Kim,Eun Jin Yang,Kohei Matsuno,Eun Jung Choy,Hyoung Sul La

doi:10.3389/fmars.2020.00612

Jee-Hoon Kim, Sung-Ho Kang + Show 6 more

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https://doi.org/10.3389/fmars.2020.00612

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Abstract

The Bering Strait is the only gateway to the Chukchi Sea from the Pacific Ocean and is a major route of Pacific water inflow. We recently investigated the occurrence of Pacific copepod species along with the warming of the Chukchi Sea and sought to identify the cause of the mass occurrence these copepods through an analysis of the water masses flowing through the Bering Strait. Zooplankton and Conductivity-Temperature-Depth (CTD) data collection was conducted in the Chukchi Sea and Bering Strait from 2014 to 2016. In addition, mooring systems installed in the Bering Strait were analyzed to obtain water temperature and salinity data during summer to understand the properties of the water masses. In 2015, a high abundance of Pacific copepod species (Eucalanus bungii, Metridia pacifica, and Neocalanus spp.) was observed in Bering Summer Water (BSW), which was relatively warm compared to measurements obtained from 2014 and 2016. As further confirmation, our results were consistent with 2007, 2009, and 2012 data, which showed that the abundance of Pacific copepod species was proportional to the temperature of the BSW entering the Chukchi Sea. In conclusion, we reconfirmed that Pacific copepod species are entering the Chukchi Sea along with BSW, and we newly discovered that their high abundance coincides with the relatively warm BSW, not Alaskan Coastal Water (ACW). These findings suggest that the inflow of the high-temperature BSW (>3°C) plays an important role in the mass occurrence of Pacific copepod species in the southern Chukchi Sea

Highlights

Large amounts of Pacific heat, nutrients, freshwater, and biota pass through the shallow Bering Strait and into the Chukchi Sea, entering the Arctic (Pickart et al, 2010; Corlett and Pickart, 2017; Danielson et al, 2017)
Like the Arctic Ocean, the Chukchi Sea exhibits a predominance of copepods in terms of zooplankton abundance and biomass (Kosobokova and Hopcroft, 2010; Ershova et al, 2015b; Smoot and Hopcroft, 2017; Carstensen et al, 2019; Kasyan, 2020), larvaceans and meroplankton contribute to the abundance and biomass of the zooplankton community during summer (Lane et al, 2008; Matsuno et al, 2016)
We focused on the relationship between the occurrence of Pacific copepod species and water masses to elucidate the cause

Summary

Introduction

Large amounts of Pacific heat, nutrients, freshwater, and biota pass through the shallow Bering Strait and into the Chukchi Sea, entering the Arctic (Pickart et al, 2010; Corlett and Pickart, 2017; Danielson et al, 2017). Pacific Copepods Occurrence in SCS environment (e.g., rising water temperatures and melting ice) of the Chukchi Sea (Shimada et al, 2006; Brugler et al, 2014; Wood et al, 2015; Pickart et al, 2016). The increasing water temperature and Pacific water inflow are causing changes in the zooplankton community across the Arctic boundary (Nelson et al, 2009). Among these changes is the appearance, reported in previous studies, of a large number of Pacific copepod species (Eucalanus bungii, Metridia pacifica, and Neocalanus spp.) in the Chukchi Sea since the late 2000s (Matsuno et al, 2011; Ershova et al, 2015a,b). To verify the response of marine organisms and their communities to changes in the marine environment, it is necessary to observe oceanographic environmental factors over the long term

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