마니크로네시아 연방 축 환초 라군의 식물플랑크톤 군집 구조

Abstract

Tropical atoll lagoons have been described as a biological oases, isolated in an extremely oligotrophic ocean. Coral reef systems within the tropical atoll lagoons are among the most productive and biologically diverse ecosystems on earth. However, little is known about phytoplankton community structure in tropical lagoon, and whether and how its composition differs from that in the adjacent ocean. To better understand phytoplankton ecosystem of this tropical lagoon, a survey was conducted in the Chuuk Lagoon, near Weno Island and the Northeast passage. Physical characteristics(temperature and salinity), nutrient concentrations, phytoplankton biomass(chlorophyll a) and phytoplankton community structure were examined for a total of nine stations in the Chuuk atoll lagoon, Federated States of Micronesia. The temperature and salinity of surface waters ranged 28.41-28.86℃ and 33.9-33.99PSU, respectively, and relatively a little higher temperature was observed near Weno Island, and a little higher salinity was observed in the passage. The surface water TIN(total inorganic nitrogen) and phosphate concentrations were 0.09～0.20μM and 0.02～0.04μM, respectively, where higher concentrations were observed inside of the lagoon than the passage albeit showing the characteristic of oligotrophic environment. Pico-fraction(<3㎛) of total chlorophyll-a ranged 65.3～88.2%. This high pico-fraction chlorophyll-a was observed both inside and outside of the lagoon. The abundance of cyanobacteria Prochlorococcus and Synechococcus was 1.24x106～52.50x106 cells/ℓ and 13,17x106～39,97x106 cells/ℓ, respectively. Synechococcus showed higher concentrations within the Chuuk Lagoon and showed a decreasing trend toward the passage whereas lower concentrations was observed for Prochlorococcus inside of the lagoon. The abundance of autotrophic flagellates ranged 5.32x104～13.34x104cells/ℓ showing higher numbers inside of the lagoon. The coccolithophores concentrations were 0.64x103～4