Interannual and seasonal changes in zooplankton community in a monsoonal coastal bay

Abstract

Environmental and zooplankton data were analyzed over a 10-year period (2001–2010) to investigate interannual and seasonal patterns of zooplankton dynamics and to identify major factors controlling these dynamics at an estuarine station in the southern coastal waters of Korea. There was a strong positive association in the interannual variation between freshwater discharge and copepod abundance, even though phytoplankton biomass was negatively associated with runoff. Copepod abundance was lowest in the summer when the abundance of predators such as chaetognaths and Noctiluca scintillans was highest. The high density of heterotrophic dinoflagellates (>103 cells m-3) adversely affected both the copepod abundance and, more markedly, the zooplankton diversity. Both the interannual pattern of zooplankton richness and the ratio of gelatinous zooplankton abundance to that of copepods increased with the increase in salinity and temperature following reduced river discharge. The overall shift in the zooplankton community during the study period may indicate range expansion of warm water zooplankton from offshore waters as well as better environmental conditions for them to grow in this bay water. This outcome also appears to reflect ecological processes related to the increase in sea surface temperature that has been underway in the offshore waters.tation in the southern coastal waters of Korea. There was a strong positive association in the interannual variation between freshwater discharge and copepod abundance, even though phytoplankton biomass was negatively associated with runoff. Copepod abundance was lowest in the summer when the abundance of predators such as chaetognaths and Noctiluca scintillans was highest. The high density of heterotrophic dinoflagellates (>103 cells m-3) adversely affected both the copepod abundance and, more markedly, the zooplankton diversity. Both the interannual pattern of zooplankton richness and the ratio of gelatinous zooplankto