Copepod Assemblages of the Northern South China Sea

COPEPOD ASSEMBLAGES OF THE NORTHERN SOUTH CHINA SEA

LI-CHUN TSENG1), HANS-UWE DAHMS1), QING-CHAO CHEN2) and JIANG-SHIOU HWANG1,3) 1) Institute of Marine Biology, National Taiwan Ocean University, 2 Pei-Ning Road, Keelung 202, Taiwan 2) South China Sea Institute of Oceanography, Chinese Academy of Sciences, Guangzhou, China

ABSTRACT We studied copepod assemblages in the northern South China Sea during October 2004. A total of 78 copepod species was identiﬁed from 24 families and 42 genera that include the four orders Calanoida, Cyclopoida, Harpacticoida, and Poecilostomatoida. The high copepod diversity in the study area may mainly be caused by both the year-round Kuroshio Current intrusion and the SW monsoon, prevailing in the South China Sea during summer. Water currents in the region transport marine planktonic fauna, that comprises predominantly Copepoda from subtropical and tropical water masses. Calanus sinicus did not appear, indicating that there was no cold water mass intrusion in that area during October 2004. Clausocalanus furcatus and C. arcuicornis were most dominant, occurring in 27 of a total of 28 samples (occurrence rate (OR): 96.43%). Thirteen copepod species were found once in all samples. The three most dominant copepods considering all samples were Clausocalanus furcatus (RA: 15.32%), C. arcuicornis (RA 13.52%), and Paracalanus nanus (RA: 9.28%). Most species of copepods performed a common diel vertical migration, descending during daytime and ascending at night at different rates to different depth zones. There were smaller numbers of species and lower diversity indices in surface waters (1-2 m depth) as compared to depths below 50 m.

ZUSAMMENFASSUNG Copepoden Gemeinschaften des nördlichen Südchinesischen Meeres waren Gegenstand einer Untersuchung im Oktober 2004. Insgesamt 78 Copepodenarten aus 24 Familien und 42 Gattun- gen und vier Ordnungen (Calanoida, Cyclopoida, Harpacticoida und Poecilostomatoida) konnten dort bestimmt werden. Die hohe Diversität im Untersuchungsgebiet wird massgeblich auf den ganzjährigen Einﬂuss eines westlichen Zweiges der Kuroshio Strömung und den im Sommer im Süchinesischen Meer vorherrschenden Südwestmonsoon zurückgeführt. So erzeugte Strömungen bringen marines Plankton in die Region, das von den Copepoda aus subtropischen und tropischen Wassermassen dominiert wird. Calanus sinicus konnte nicht gefunden werden was einen Kaltwasser- masseneinﬂuss in der Region im Oktober 2004 ausschliesst. Clausocalanus furcatus und C. arcuicornis waren dominant, und in 27 von 28 Proben vertreten (Präsenz (OR): 96,43%). Dreizehn Copepo- denarten konnten in allen Proben nachgewiesen werden. Die drei in allen Proben vorherrschenden

3) Corresponding author; Fax: +886.224629464; e-mail: [email protected] © Koninklijke Brill NV, Leiden, 2008 Crustaceana 81 (1): 1-22 Also available online: www.brill.nl/cr 2 LI-CHUN TSENG ET AL.

Copepodenarten waren Clausocalanus furcatus (RA: 15,32%), C. arcuicornis (RA: 13,52%), und Paracalanus nanus (RA: 9,28%). Die meisten Copepodenarten zeigten tägliche Vertikalwanderun- gen, mit einer Wanderung in die Tiefe tagsüber und einer gegenläufigen Wanderung nachts, aber artspezifischen Trends. Im Oberflächenwasser (1-2 m Tiefe) konnten geringere Diversitäten (Arten- zahlen und Diversitätsindizes) festgestellt werden als in Tiefen unterhalb 50 m.

INTRODUCTION The complexity of oceanic circulations around the island of Taiwan generates a high diversity of marine life, comprising about 10% of the world’s total marine fauna, and including a large number of endemic species (Shao, 1998; Hwang et al., 2000a). Such high diversity is suggested to be enhanced by ocean currents and water movements that also affect the structure of copepod communities at spatial and temporal scales. Along the Taiwan Strait and the southern edge of the East China Sea, water circulations are strongly influenced by monsoon winds. During the NE monsoon period in winter (September to April), the China Coastal Current brings cold water from the Yellow Sea and from the East China Sea to the Taiwan Strait (Lee & Chao, 2003; Liang et al., 2003; Liu et al., 2003; Tseng & Shen, 2003). Water circulation in this area varies seasonally with changes in wind direction (Jan et al., 1995, 2002; Lee & Chao, 2003; Liang et al., 2003; Tseng & Shen, 2003). Physical oceanography indicates that the Kuroshio Current intrudes into both the northern South China Sea and the coastal waters of southern Taiwan via the Lu- zon Channel, particularly during winter (Jan et al., 1995, 2002). Recently, Hwang & Wong (2005) have used Calanus sinicus Brodsky, 1962 as a biological indicator to trace water movements. They suggested that during the NE monsoon prevailing in winter, Calanus sinicus has been transported from the Bohai Sea, the Yellow Sea, and the East China Sea to the waters north of Taiwan and along the China coast southwards to the waters of Hong Kong. The Luzon Channel is an important water way transporting marine fauna from the Kuroshio Current towards the northern South China Sea and the coastal waters of southern Taiwan (Hwang et al., 2006). The diel vertical migration (DVM) process is a reasonable cause of assemblage shifts in certain water layers. Particularly in the subtropical waters of the present study, both thermal stratification and upwellings may not be efficient enough to act as a barrier to limit the DVM of copepods. Different copepods and different stages of the same species may prefer different depth zones and perform different patterns of DVM. Furthermore, multiple biotic and abiotic factors, such as food abundance and distribution, predation pressure, and hydrographical heterogeneities, may interactively influence the DVM of copepods. The objective of this study was to investigate spatial patterns of copepod biodiversity at six stations of the northern South China Sea, and the diel vertical