CHARACTERISTIC DISTRIBUTION OF PHYTOPLANKTON AND BACTERIA IN THE ENVIRONMENTAL TRANSITION ZONE OF TROPICAL MANGROVE FOREST

Abstract

Mangrove forests play important roles in nutrients cycling and primary production in the tropical marine ecosystems. In order to understand phytoplankton and bacterial distribution in tropical coral reef ecosystems in relation to mangrove waters, their biomass and activities were measured in seawater of the Chuuk and the Kosrae lagoons of Micronesia. Chlorophyll-a and bacterial abundances showed maximal values in the seawaters near the mangrove forests, and then steeply decreased along the distance away from, indicating that environmental conditions for these microorganisms changed greatly in lagoon waters. Chlorophyll-a, cyanobacteria and phototrophic picoeukaryote abundances as well as a variety of indicator pigments for photosynthetic eukaryotes showed similar spatial distribution patterns, suggesting that phytoplankton assemblages may respond to the environmental gradient by changing community compositions. In addition, primary production and bacterial production were also higher in the bay surrounded by mangrove forest and lower at outside of the lagoon. These results suggested that waters of mangroves forests in the tropical system may contribute significant proportion in total energy production and nutrient cycling in tropical coastal ecosystems.aters, their biomass and activities were measured in seawater of the Chuuk and the Kosrae lagoons of Micronesia. Chlorophyll-a and bacterial abundances showed maximal values in the seawaters near the mangrove forests, and then steeply decreased along the distance away from, indicating that environmental conditions for these microorganisms changed greatly in lagoon waters. Chlorophyll-a, cyanobacteria and phototrophic picoeukaryote abundances as well as a variety of indicator pigments for photosynthetic eukaryotes showed similar spatial distribution patterns, suggesting that phytoplankton assemblages may respond to the environmental gradient by changing community compositions. In addition, primary production and bacterial production were also higher in the bay surrounded by mangrove forest and lower at outside of the lagoon. These results suggested that waters of mangroves forests in the tropical system may contribute significant proportion in total energy production and nutrient cycling in tropical coastal ecosystems.