Monsoon driven seasonal succession of copepod assemblages in the coastal waters of the northeastern Taiwan Strait.

Abstract

Monsoon-driven succession of copepod assemblages in coastal waters of the northeastern Taiwan Strait. Zoological Studies 47(1): 46-60. Monsoon winds (a southwesterly (SW) monsoon during summer and a northeasterly (NE) monsoon during winter) were shown to play pivotal roles in shaping species richness and diversity of planktonic organisms in the water masses of the Taiwan Strait (TS). We investigated monsoon-related variations in copepod assemblages in the northeastern TS from Aug. 1998 to May 1999 on 4 research cruises. Our data provide basic information for the biological monitoring of the TS, using improved index measurements. In total, 36 copepod species belonging to 21 genera and 14 families were identified. The abundance of Calanoida showed a negative correlation with salinity (r=-0.381, p=0.011, Pearson's product moment correlation) and a positive correlation with temperature (r=0.662, p＜0.001, Pearson's product moment correlation). Application of the indicator value index proposed by Dufrêne and Legendre indicated that cold-water species become dominant in this region only when the NE monsoon weakens and retracts from the southern part of the TS. Regardless of the seasonal succession, the calanoid copepod, Acrocalanus gibber, was the dominant species with a mean density of 3868 individuals (ind)/1000 m^3 (with a relative abundance of 36.5%), followed by Acartia erythraea with a mean density of 1874 ind/1000 m^3 (17.7%), and by Labidocera euchaeta with a mean density of 1178 ind/1000 m^3 (11.1%). Four copepod communities were distinguished prior to the advent of the NE and SW monsoonal winds and during the peak periods of the respective monsoons. Our results also reveal the influence of the Kuroshio Branch Current in the study area on copepod assemblages, with temporal successions being determined by the SW and NE monsoonal winds.