The coexistence of seagrass and coral at Bise, Okinawa, Japan

Abstract

Interaction between the seagrass Thalassia hemprichii and the coral Montipora digitata in the combined community at Bise was investigated by using dome type of chamber incubations at in situ. Nutrient dynamic, dissolved organic carbon (DOC) and microbial community in four habitats as sand, seagrass, coral and seagrass with coral (sg+cr) were examined. Experiments were conducted for 24 hours under the natural light and temperature. Coral habitat showed higher dissolved oxygen (DO) values than other habitats. In this experiment, DO was significantly negatively correlated with alkalinity (r = 0.48, p ≤ 0.01, n = 28). Alkalinity values were higher in seagrass habitat due to the lack of capacity of the seagrass Thalassia hemprichii to use bicarbonate from the surrounding water while, in coral habitat low alkalinity values than other habitats were found due to coral calcification. Influence of ground water lead to high increased of nitrate in the seagrass habitat. During the light period, DOC concentrations were high in seagrass habitat whereas, the high value of DOC during the dark period in coral habitat was found due to mucus released from coral. Increased of organic matter in the surrounding water leads to increase of microbial abundance, therefore high abundance of bacteria in seagrass habitat was exhibited. In sg+cr habitat, bacterial abundance was lower than other habitats whereas, DO, Interaction between seagrass and coral |16 pH, nutrients and DOC values were exhibited intermediate values between seagrass habitat and coral habitat. In the combined community, DOC was supported from seagrass exudation, while coral supply dissolved oxygen and carbon dioxide during calcification process.