Changing Distributions of Zooplankton Communities in a Coastal Lagoon in Response to Rainfall Seasonality

Abstract

Choi, J.-Y.; Kim, J.-C., and Kim, S.-K, 2020. Changing distributions of zooplankton communities in a coastal lagoon in response to rainfall seasonality. In: Jung, H.-S.; Lee, S.; Ryu, J.-H., and Cui, T. (eds.), Advances in Geospatial Research of Coastal Environments. Journal of Coastal Research, Special Issue No. 102, pp. 69-74. Coconut Creek (Florida), ISSN 0749-0208.Coastal lagoons are unique and complex ecosystems which exhibit very high primary and secondary production rate, and their productivity is underpinned by plankton communities. Empirical studies suggest that summer rainfall determines the spatial and temporal pattern of not only physicochemical variables but also zooplankton communities in coastal regions. It was hypothesized that drier or wetter than average summer rainfall years would change the environmental variables (e.g., salinity, dissolve oxygen, and nutrients) in coastal lagoons, thereby disrupting the spring growth trend of zooplankton communities. Long-term (2014–2017) monitoring data (rainfall, environmental variables, and zooplankton) were divided into two groups: Rainy and Dry years, corresponding to years with an annual rainfall that was higher or lower than the total annual average, respectively. The results showed that summer and autumn densities of zooplankton fell sharply in Rainy years but increased steadily in Dry years. The highest density of rotifers was mainly observed in sites adjacent to the inflow of tributary streams, while copepods were abundant near the outlet to the ocean. The differing spatial distribution of rotifers and copepods is attributed to the salinity gradient in the study site, and changed with freshwater inflows. Based on these findings, it is suggested that summer rainfall variations play an important role in driving the spatial and temporal distribution of zooplankton.