Abstract

The Yellow Sea Bottom Cold Water (YSBCW) refers to seawater with a water temperature of 10 °C or less found at the bottom of the center of the Yellow Sea. The spatiotemporal variability of the YSBCW directly affects the distribution of organisms in the marine ecosystem. In this study, hydroacoustic and net surveys were conducted in April (spring) to understand the spatial distribution of the sound scattering layer (SSL) and estimate the density of Euphausia pacifica (E. pacifica) in the YSBCW. Despite the shallow water in the YSBCW region, E. pacifica formed an SSL, which was distributed near the bottom during the daytime; it showed a diel vertical migration (DVM) pattern of movement toward the surface during the nighttime. The mean upward and downward swimming speeds around sunset and sunrise were approximately 0.6 and 0.3–0.4 m/min, respectively. The E. pacifica density was estimated in the central, western, and eastern regions; the results were approximately 15.8, 1.3, and 10.3 g/m2, respectively, indicating significant differences according to region. The results revealed high-density distributions in the central and eastern regions related to the water temperature structure, which differs regionally in the YSBCW area. Additional studies are needed regarding the spatial distribution of E. pacifica in the YSBCW and its relationship with various ocean environmental parameters according to season. The results of this study contribute to a greater understanding of the structure of the marine ecosystem in the YSBCW.

Highlights

  • Published: 4 January 2022The Yellow Sea, a semi-enclosed marginal sea located between the Korean peninsula and the China mainland, is connected to the northwestern Pacific Ocean and has a mean depth of approximately 44 m [1]

  • It was confirmed that Copepoda consisted of individuals less than 2 mm in L, and Euphausiacea mainly consisted of juvenile and adults of E. pacifica

  • It is assumed that the density of E. pacifica was related to the water temperature

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Summary

Introduction

The Yellow Sea, a semi-enclosed marginal sea located between the Korean peninsula and the China mainland, is connected to the northwestern Pacific Ocean and has a mean depth of approximately 44 m [1]. The maximum water depth in the central part of the sea, which has the characteristics of a continental shelf, is less than approximately. The Yellow Sea Bottom Cold Water (YSBCW), an important oceanic phenomenon in the Yellow Sea, occurs from spring to autumn at the bottom of the central area [3,4]. The. YSBCW, which occupies more than 70% of the total area of the Yellow Sea, has a low water temperature of less than 10 ◦ C and a high salinity of 32–33 practical salinity unit (psu) [5,6].

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