Distributions of Nutrients in Relation to Phytoplankton Community Heterogeneity in the Makassar Strait, Indonesia

Abstract

The Monitoring of Indonesia Throughflow (MITF) with scientific cruise across the Indonesian waters that are connecting the islands of Kalimantan and Sulawesi or strait of Makassar. This cruise carried out in August 2015 in an area between 2° and 4° South and 118° and 119° East. This cruise aims to characterize the concentration of nutrients and abundance of phytoplankton groups as well as explain their distribution based on the environmental conditions. Nutrient concentrations consisting of Inorganic Dissolved Nitrogen (DIN), Inorganic Dissolved Phosphate (DIP) and Inorganic Dissolved Silicate (DSi) were measured at seven depth layers, i.e. 10, 30-60, 100-150, 300, 500, 750 and 1000 meters. The study showed that in the transitional season (August), the upper layer of study sites were characterized by salinity between 34.05 and 34.76 PSU, temperature between 26.85 and 29.88 °C, and relatively high nutrient concentration, i.e. DIN = 8.91-36.74 μM, DIP = 0.02-0.16 μM, and DSi= 31.88-249.49 μM. The phytoplankton community groups found were Cyanophyta, Bacillariophyta (Diatom), and Dinophyta, where the highest abundance was Cynophyta for the genus Trichodesmium sp. The composition of phytoplankton community in the surface layer is strongly influenced by sea surface temperature, salinity and nutrient concentration. We found that nutrient utilization in the surface layer is relatively high.