Species composition and abundance of zooplankton community in spring and autumn around Dokdo

Abstract

Species composition and abundance of zooplankton were investigated around Dokdo in the East/Japan Sea in autumn 1999 and spring 2000. Vertical and horizontal hauls of a bongo net (300 μm mesh size, 60 cm diameter) were made to collect zooplankton sample. Surface temperature and salinity ranged from 24.2°C to 25.1°C, and from 32.9 psu to 33.2 psu in September 1999, respectively. In May 2000, surface temperatures were 13.9°C and 14.2°C at stations of A1 and A8, and salinity was 34.5 psu at both stations. Zooplankton community was dominated by copepods which comprised 61% (September) and 60% (May) of total numerical abundance, respectively. The next dominant groups were appendicularians (11%) and chaetognaths (9%) in September 1999, and other crustaceans (27%) and appendicularians (4%) in May 2000. The 15.7% (September) and 23.2% (May) of copepods were in the juvenile stage of copepodite. The most dominant copepods were Oncaea media (10.4%) and Clausocalanus sp. (8.2%) which preferred warm water in September. In contrast, cold-water copepods such as Pseudocalanus minutus (9.4%) and Metridia pacifica (8.0%) were dominant in May. The results of cluster analysis based on Bray-Curtis index showed that zooplankton community were classified into two groups which represented different water mass. The average abundance of zooplankton in September was 2.1 times higher than that in May, and species number of them in September outnumbered that in May by 29 species. Zooplankton community varied in associated with a characteristic of warm waters which affected marine ecosystem differently in the study area depending on seasons.