Abstract
The coastal water transported by the combined action of southwest wind jet and anticyclonic eddy substantially influences the biological processes in the midwestern South China Sea. However, how the wind-driven jet affects the zooplankton community remains unclear. In this study, the species number, abundance, and vertical distribution of medusae were investigated in the wind-driven jet (WJR) and non-wind-driven jet regions (NWJR). The low-salinity and nutrient-rich coastal water substantially influenced species composition, abundance, and vertical distribution of medusae in the WJR. The species number of the meroplanktonic hydromedusae in the WJR was approximately twice that in the NWJR due to the horizontal transport of wind-driven jets. The abundances of holoplanktonic hydromedusae in WJR were 38.2 ± 9.3 ind⋅m–3, which were thrice of that in the NWJR regions, caused by the abundant diet in the WJR. Additionally, only the abundance of medusae above the thermocline was affected by the coastal water in WJR, while these showed no significant difference below the thermocline between the WJR and the NWJR. Generalized additive model analyses suggested that the diet was the most important factor affecting the abundance of the holoplanktonic hydromedusae and siphonophore, whereas meroplanktonic hydromedusae were influenced by the combination of temperature, salinity, and diet.
Highlights
The South China Sea (SCS) is a semienclosed ocean basin and the largest marginal sea in Asia
We addressed two key questions with our study: (1) Does the coastal water transported by wind-driven jet affect the community structures and vertical distributions of medusae in the WJR? (2) How does the coastal water affect medusae in the WJR? These results significantly advance our understanding of the community structure of pelagic cnidarians in the midwestern SCS and highlight the role of coastal water intrusion in pelagic ecosystems in the open sea
Low salinity was characteristic of the surface water of TC, which indicated that the TC was influenced by the coastal water
Summary
The South China Sea (SCS) is a semienclosed ocean basin and the largest marginal sea in Asia. The SCS is affected by the southwest monsoon, which induces offshore Ekman transport and brings upwelling near the coast of southeast Vietnam (Xie et al, 2003, 2007; Li et al, 2014; Da et al, 2019; Ngo and Hsin, 2021). The wind curl force of the southwest wind jet causes the double gyre circulation to form in the SCS with a northern cyclonic gyre and a southern anticyclonic gyre (Kuo et al, 2000; Metzger, 2003; Da et al, 2019; Ngo and Hsin, 2021). The cold coastal water could spread eastward over most of the central SCS (approximately 115◦E) in summer (Xie et al, 2003; Chen et al, 2021). The complex physical dynamic processes of the wind jet in the midwestern SCS attracted a lot of attention (Ning et al, 2004; Liu et al, 2012; Chen et al, 2014)
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