2003년 여름 장목만 정점에서 식물플랑크톤의 일변화

Abstract

Daily changes in phytoplankton abundance and species composition were monitored from July to September 2003 (n=47) in order to understand which factors control the abundance at a station in Jangmok Bay. The phytoplankton community was mainly composed of small cell diatoms and dinoflagellates, and the dominant genera were Chaetoceros, Nitzschia, Skeletonema and Thalassionema. On the basis of the N/P and Si/N ratios, the sampling period could be divided into two periods such as an inorganic silicate limitation period (ISLP, 14th July-12th of August) and an inorganic nitrogen limitation period (INLP, 13th of August - the end of the study), suggesting that P was not an important limiting nutrient for phytoplankton growth in the Bay. Twelve high concentrations (>3x106 cells/l) and eight low concentrations (<3x105 cells/l) of the phytoplankton abundance were encountered during the ISLP and the INLP, respectively. The replacement of diatoms by dinoflagellates appeared to start when the Si/N ratio became high, and then dinoflagellates dominated during the INLP. Blooms by harmful algal species were not detected and harmful algal species were not abundant. On the basis of chlorophyll-a concentrations, nanophytoplankton was a major component and the picophytoplankton was also not negligible. We found that during the study the phytoplankton abundance had significant relationships with temperature and salinity, and positive relationship with NO2 and mesozooplankton. This study suggests that the phytoplankton abundance might be mainly controlled by resource limitation (bottom-up), and that although there appeared to be a predation effect of mesozooplankton (top-down) it may not be significant.