Feeding activity of the copepod Acartia hongi on phytoplankton and micro-zooplankton in Gyeonggi Bay, Yellow Sea

Abstract

In order to improve our understanding of the trophic link between microzooplankton and copepods in Gyeonggi Bay, Yellow Sea, we estimated diet composition, ingestion rates and prey selectivity of Acartia hongi, known as the most abundant and widespread copepod species, conducting in situ bottle incubation throughout the different seasons. The results showed that A. hongi preferentially grazed on ciliate and heterotrophic dinoflagellate with size ranging from 20 to 100 ？m over phytoplankton. Although microzooplankton comprised only the average 13.7% of the total carbon available in the natural prey pool, microzooplankton accounted for > 70 % of the total carbon ration ingested by A. hongi throughout the year except for winter diatom blooming periods, when A. hongi obtained about 60% of its carbon ration from phytoplankton. Our results demonstrated that: (i) A. hongi modified their diet composition and feeding rates in response to change in composition and size of prey available to them, and (ii) A. hongi preferentially ingested microzooplankton over phytoplankton. Therefore, feeding activity of A. hongi could affect the species composition and size structure of natural plankton communities in this study area, particularly regarding microzooplankton. Thus, strongly selective feeding and high grazing pressure by A. hongi on microzooplankton implicate trophic coupling between copepods and the microbial food web in the pelagic ecosystem of Gyeonggi Bay.