Community structure of planktonic copepods in I-Lan Bay and the adjacent Kuroshio waters off northeastern Taiwan

Abstract

Our knowledge on seasonal fluctuation of the planktonic copepods in the waters off northeastern Taiwan is limited. To estimate whether the regional fishery production is at a reasonable level or not, the study of marine copepods could be necessary. Plankton samples for copepod studies were collected by a ring trawl net with 335 μm mesh size at five fixed stations along a transect extending eastward from I-Lan Bay to about 40 nautical miles (approx. 72 km) offshore, in 2004. A total of 137 species of copepods belonging to 4 orders, 25 families, and 53 genera were identified. Twentysix dominant species contributed to the main components of seasonal abundance of the copepod community. Four of these, i.e., Cosmocalanus darwini, Clausocalanus minor, Oithona plumifera, and Oncaea venusta, were the most widely distributed species that occurred at all stations in each season. The principal results have shown that copepod abundance was higher in the continental shelf waters and lower in the Kuroshio waters, but the number of species was higher in the Kuroshio waters than that on the continental shelf, except in autumn. Apparent seasonal fluctuations in the composition of dominant species were observed by replacement rates at all stations. Geographical variation in distributional associations of the copepod community occurred over a seasonal scale, and the intermediate region was mainly influenced by the Kuroshio Current. Calanus sinicus might be considered an indicator species for the intrusion of eddy waters from the East China Sea into I-Lan Bay and its adjacent waters. Notre connaissance des fluctuations saisonnieres des copepodes planctoniques dans les eaux au large du nord-est de Taiwan est limitee. Afin d'estimer si la production regionale des peches se situe a un niveau raisonnable, l'etude des copepodes marins pourrait s'averer necessaire. Des echantillons de plancton destines aux etudes de copepodes ont ete recoltes a l'aide d'un filet a plancton de 335 μm de vide de maille sur 5 stations fixes sur un transect s'etendant vers l'est, de I-Lan Bay jusqu'a environ 40 miles nautiques (environ 72 km) au large, en 2004. Un total de 137 especes de copepodes appartenant a 4 ordres, 25 familles, et 53 genres ont ete identifiees. Vingt-six especes dominantes constituaient les elements principaux de l'abondance saisonniere de la communaute de copepodes. Quatre d'entre elles, Cosmocalanus darwini, Clausocalanus minor, Oithona plumifera et Oncaea venusta, etaient les plus largement reparties, presentes dans toutes les stations a chaque saison. Les principaux resultats ont montre que l'abondance des copepodes etait superieure dans les eaux du plateau continental, et inferieure dans les eaux du Kuroshio, mais le nombre d'especes etait plus eleve dans les eaux du Kuroshio que sur le plateau continental, sauf en automne. Les fluctuations saisonnieres apparentes de la composition des especes dominantes ont ete observees par des taux de remplacement a toutes les stations. La variation geographique des associations de distribution dans la communaute de copepodes existe a l'echelle de la saison, et la region intermediaire est principalement influencee par le courant du Kuroshio. Calanus sinicus peut etre consideree comme une espece indicatrice de l'intrusion de courants venant de la mer de Chine orientale dans la baie de I-Lan et ses eaux adjacentes.