Mesozooplankton trends at a coastal station in Jinhae Bay, Korea

Abstract

Mesozooplankton and environmental data were analyzed over a 10-year period (2001&#8211 2010) to investigate seasonal and interannual patterns of mesozooplankton dynamics and to identify the main factors controlling these dynamics at a coastal station in Jinhae Bay of Korea. The total mesozooplankton abundance showed no significant trend but the interannual variation was characterized by two noticeable increases and decreases in the cumulative totals. Copepods, the most dominant group among the major groups of mesozooplankton, displayed no significant variation in their abundance during the 10 years. In contrast, the abundance of cladocerans, meroplankton, and gelatinous zooplankton increased significantly, and gelatinous zooplankton in particular displayed the most distinctive increasing trend. The 20 most dominant taxa were responsible for over 95% of the total mesozooplankton abundance, and this proportion displayed little interannual variation (~2.0%). Among the dominant taxa, eight (Acartia steueri, Oikopleura spp., Oithona spp., polychaete larvae, molluscan veliger, cirripede larvae, hydromedusae, and Evadne tergestina) displayed significantly increasing trends, whereas three (Acartia omorii, decapod larvae, Calanus sinicus) had decreasing trends during the 10-year period. However, why these dominant taxa either increased or decreased in relation to environmental factors has not been clearly determined. According to the results of a redundancy analysis (RDA) on environmental factors and the mesozooplankton community, sea surface temperature (SST), salinity, and rainfall significantly influenced the seasonal and interannual variations of the mesozooplankton community. Significant trends were detected in the species diversity of the mesozooplankton community, and the constant increase during the winter season led to interannual variations. The overall shift in the mesozooplankton community during the study period may indicate a range expansion of warm water mesozooplankton from offshore locations into the bay. This also appears to reflect ecological processes related to the increase in SST observed in the offshore waters.