A Stable Isotope Study of the Relationship between Coral Tissues and Zooxanthellae in a Seasonal Tropical Environment of East Kalimantan, Indonesia

This study assessed variations in the relationship between zooxanthellae and their coral hosts seasonally and spatially. Carbon and nitrogen stable isotopes (d13C and d15N) were used to analyze the patterns of nutritional transport between coral and zooxanthellae. Studies of temporal differences were conducted during two dry seasons and one rainy season in the Berau Marine Conservation Area, East Kalimantan, Indonesia. To assess spatial variations, coral samples from three genera (Porites, Seriatopora and Stylophora) were collected from three localities, designated as nearest, medium, and farthest from the Berau River mouth. The lower d13C of Seriatopora compared with the other two genera suggested that corals in this genus were more actively utilizing particulate organic matter and adopting a heterotrophic feeding mode. The d13C values of coral tissue and zooxanthellae also were affected by differences in seasons, localities, and depth, whereas the d15N values varied significantly with seasons alone. Differences in d15N values between coral tissue and zooxanthellae were always positive in the first and second dry seasons, but negative in the rainy season. This finding indicated that zooxanthellae were the main source of coral nutrients during the dry season, while host coral may support zooxanthellae nutrition during rainy season of low turbidity. Spatially, sedimentation does not show significant impact to the relationship between coral and zooxanthellae.