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Copepoda, Calanoida, Calanidae) in Northern Coastal Waters of Taiwan During the Northeast Monsoon Period

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Copepoda, Calanoida, Calanidae) in Northern Coastal Waters of Taiwan During the Northeast Monsoon Period DIET OF THE COPEPOD CALANUS SINICUS BRODSKY, 1962 (COPEPODA, CALANOIDA, CALANIDAE) IN NORTHERN COASTAL WATERS OF TAIWAN DURING THE NORTHEAST MONSOON PERIOD BY MING-REN CHEN, SAMBA KÂ and JIANG-SHIOU HWANG1) Institute of Marine Biology, National Taiwan Ocean University, Keelung 202, Taiwan ABSTRACT The calanoid copepod, Calanus sinicus is transported into Taiwanese waters during the northeast (NE) monsoon season, during which time cold waters make incursions into Taiwanese coastal areas. Little is known about the feeding ecology of this copepod. We investigated the gut contents of C. sinicus using scanning electron microscopy (SEM). Samples were collected in northern coastal waters of Taiwan in January 2005. Gut content analysis of copepodites stage V (CVs), females, and males showed a large part of their gut contents as unidentifiable chyme, marine snow, or fragments of phytoplankton. However, C. sinicus fed mainly on diatoms and also a little on protozoans, dinoflagellates, bacteria, and coccoliths. Male dietary gut contents differed in composition from that of CVs and females. Additionally, gut fullness shows a significant difference between CVs, females, and males, with the highest ratio observed in females and the lowest in males. There was an offset in time between gut fullness of male and female copepodites. Thus, we suggest C. sinicus is omnivorous, but this species feeds primarily on phytoplankton with some variations in the course of its ontogeny. In conclusion, C. sinicus adapted rapidly and fed on endemic plankton as its main food source in the waters of Taiwan during the NE monsoon. RÉSUMÉ Le copépode calanoide Calanus sinicus est transporté dans les eaux taïwanaises pendant la mousson du nord-est (NE), saison durant laquelle des eaux froides font des incursions dans les zones côtières taïwanaises. L’écologie alimentaire de ce copépode est très peu connue. Nous avons étudié les contenus stomacaux de C. sinicus grâce à la microscopie électronique à balayage (MEB). Les échantillons ont été prélevés dans les eaux côtières au nord de Taiwan, en Janvier 2005. Une grande partie des contenus stomacaux des copépodites V (CV), des males et des femelles étaient non identifiables apparaissant ainsi en forme de chyme, de marine snow ( neige marine )ou de fragments de phytoplancton. Toutefois, la nourriture de C. sinicus était essentiellement constituée de diatomées et dans une moindre mesure de protozoaires, de dinoflagellés, de bactéries et de coccolithes. La composition des contenus stomacaux des males différait de celle des CV et des femelles. En outre, le remplissage de l’estomac montrait une différence significative entre les CV, 1) Author for correspondence; Fax: +886 224629464; e-mail: [email protected] © Koninklijke Brill NV, Leiden, 2010 Crustaceana 83 (7): 851-864 Also available online: www.brill.nl/cr DOI:10.1163/001121610X504360 852 M.-R. CHEN, S. KÂ & J.-S. HWANG les males et les femelles, avec des ratios plus élevés observés chez les femelles et ceux plus faibles chez les mâles. Il y avait un décalage dans le temps pour le remplissage l’intestin entre les males, les femelles et les copépodites. Ainsi, nous estimons que C. sinicus est omnivore, mais se nourrit essentiellement de phytoplancton avec quelques variations ontogéniques. En conclusion, C. sinicus s’adapte rapidement dans les eaux de Taiwan pendant la mousson du NE en utilisant le plancton endémique comme principale source de nourriture. INTRODUCTION The calanoid copepod, Calanus sinicus Brodsky, 1962 is widely distributed in the shelf waters of the western North Pacific, from Japan to Vietnam. In particular, among the population centres in the Bohai Sea, Yellow Sea, and East China Sea, C. sinicus is the dominant zooplankton species, which accounts for 80% of the zooplankton biomass, suggesting its important role in the marine ecosystem (Zhu & Iverson, 1990; Chen, 1992; Huang et al., 1993a; Hulsemann, 1994; Li et al., 2003a; Hwang & Wong, 2005). C. sinicus is the main food source for several fishes, such as anchovy (Engraulis japonicus Temminck & Schlegel, 1846), sardines (Sardina pilchardus Walbaum, 1792), sand eel (Ammodytes personatus Girard, 1856), and mackerel (Scomberomorus niphonius Cuvier, 1832), that are important for the fishing industry (Zhu & Iverson, 1990; Uye et al., 1999; Islam & Tanaka, 2008). Recent studies report that C. sinicus is abundant in the waters off Taiwan during winter and early spring, because of the incursion of cold water masses from the Yellow Sea and the East China Sea during the northeast (NE) monsoon period (September to April) by the China Coastal Current (Lee & Chao, 2003; Liang et al., 2003; Liu et al., 2003; Tseng & Shen, 2003; Hwang & Wong, 2005; Hwang et al., 2006; Dur et al., 2007; Lan et al., 2008). Therefore, we, along with others, consider this species a biological indicator for the intrusion of cold water into the northern part of the South China Sea (Hwang & Wong, 2005; Hwang et al., 2006). Thus, we became interested in investigating the ecology of C. sinicus. Copepod diets are studied to understand the copepods’ significance in terms of secondary production in ocean environments (Irigoien et al., 2002). Feeding stud- ies are considered possible methods to characterize the copepod diet. Many pre- vious works on copepod feeding ecology examined faecal pellets using scanning electron microscopy (e.g., Schrader, 1971; Turner, 1977, 1984a, b, 1986, 1991, 2002; Fleddum et al., 2001; Wexels et al., 2003; Schøyen & Kaartvedt, 2004; Wu et al., 2004; Eskinazi-Sant’Anna, 2006; Jansen et al., 2006). However, faecal-pellet analysis methods to determine food preferences have some limitations, since some food remains are unrecognizable after digestion. The faecal pellets only contain undigested food items such as diatoms or shells. All food items lacking hard parts or composed only of soft tissue (e.g., flagellates) are digested and cannot be iden- tified from faecal pellets (Bathmann et al., 1987; Eskinazi-Sant’Anna, 2006). On.
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