Community structure and abundance of copepods in summer on a fringing coral reef off Ishigaki Island, Ryukyu Islands, Japan

Abstract

Mesozooplankton is an important component of coral reef ecosystems. This study investigated the community structure and abundance of copepods in the fore-reef environment around channel mouths and the adjacent offshore waters of Ishigaki Island in the summer. The fore-reef station group of copepods was significantly distinguishable from the offshore station group in terms of community structure. Unlike the fore-reef group, the offshore group showed high species diversity, low density of calanoids and was composed mainly of oceanic species. The fore-reef group was characterized by the littoral species Acartia fossae, Bestiolina similis, Oithona simplex, and Oithona dissimilis. High densities of these species were recorded near channel mouths. The pattern of tidal changes near the channel mouth accorded with the characteristics of the environment. The channel mouths might be preferred because they offer a food-rich environment for the coral reef species A. fossae, passive transportation by the ebb current for the estuarine species O. dissimilis, and reef system circulation for the euryhaline species B. similis and O. simplex. The species composition and densities of the calanoids in the fore-reef stations differed between the east and west sides of the channel mouths, suggesting tidal and topographical influences.