Water mass transport through the northern Bashi Channel in the northeastern South China Sea affects copepod assemblages of the Luzon Strait

Wen-Tseng Lo,Hans-Uwe Dahms,Jiang-Shiou Hwang

doi:10.1186/s40555-014-0066-7

Abstract

Abstract Background It is controversial to what extent the intrusion of the Kuroshio Branch Current to the Luzon Strait and the South China Sea circulation can shape copepod assemblages around southern Taiwan. We tested the hypothesis that currents such as the Kuroshio Current bring marine zooplankton and copepods from subtropical and tropical waters to the south of Taiwan. We studied copepod assemblages from the Bashi Channel in the northeastern South China Sea at the coast of southwest Taiwan during early October 1996. Results A total of 77 copepod species were identified from 34 genera that included calanoids, cyclopoids, harpacticoids, and poecilostomatoids. Several indicator species suggest that the study area is highly influenced by water masses from the northern South China Sea as well as from the Kuroshio Current. Acrocalanus gracilis (Paracalanidae, Calanoida) was most abundant (with a relative abundance (RA) of 22.07 and an occurrence rate (OR) of 100%), followed by Paracalanus aculeatus (Paracalanidae, Calanoida) and Oncaea venusta (Cyclopoida). The stations close to the Kuroshio Current showed a higher species diversity (H') and a higher species richness with 3.9 to 4.6 at moderate abundance, whereas station 11 showed lowest species diversity (H') with (2.1), accompanied by the far lowest species number (14) and abundance (880 ind./100 m3). Conclusions Several indicator species suggest that the study area is highly influenced by water masses from the northern South China Sea as well as from the Kuroshio Current.

Highlights

It is controversial to what extent the intrusion of the Kuroshio Branch Current to the Luzon Strait and the South China Sea circulation can shape copepod assemblages around southern Taiwan
The characteristic of the T/S diagram in the upper waters at station 1 was between the South China Sea Surface Current and the Kuroshio Current, while deeper zones were influenced by the warmer Kuroshio Current (Figure 2)
A total of 77 copepod species were identified from 34 genera that include calanoids, cyclopoids, harpacticoids, and poecilostomatoids (Table 1)

Summary

Introduction

The complexity of oceanic circulations around the island of Taiwan generated a high diversity of marine life, comprising about 10% of the world's total marine fauna and including a large number of endemic species Such high diversity is suggested to be enhanced by ocean currents and water movements that affect the structure of copepod communities at spatial and temporal scales. Sea to the Taiwan Strait (Liu et al 2003; Tseng and Shen 2003; Hwang and Wong 2005; Hwang et al 2006; Chang et al 2010) Water circulation in this area varies seasonally with changes in wind direction. Physical oceanography indicates that the Kuroshio Current intrudes into both the northern South China Sea and the coastal waters of southern Taiwan via the Luzon Channel, during winter (Tseng and Shen 2003). The Luzon Channel is an important water way transporting marine fauna from the Kuroshio Current towards the northeastern South China Sea and the coastal waters of southern Taiwan (Hwang et al 2006; Hsieh et al 2011; Hsieh et al 2012)

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