Effect of light and zooplankton on skeletal δ13C values in the eastern Pacific corals Pavona clavus and Pavona gigantea

Abstract

 Skeletal δ¹³C levels in symbiotic reef corals are believed to be predominantly influenced by metabolic fractionation. Therefore, environmental variables influencing coral metabolism should also affect skeletal δ¹³C levels. To test this hypothesis, we measured the effects of light (which drives photosynthesis) and relative zooplankton levels (heterotrophy) on skeletal δ¹³C values in the corals Pavona clavus and P. gigantea at two depths (1 m and 7 m). For both species, decreases in light or increases in zooplankton resulted in significant decreases in skeletal δ¹³C levels. A significant decrease in δ¹³C values with depth was observed in Pavona gigantea only. Thus, light and zooplankton directly affect coral skeletal δ¹³C values, supporting the hypothesis that metabolic fractionation significantly contributes to skeletal δ¹³C levels. Simultaneous decreases in both light and zooplankton resulted in decreases in skeletal δ¹³C values, reflecting decreases in light. In Pavona clavus, intra-annual variation in skeletal δ¹³C values over one year correlated with seasonal changes in irradiance. Further study is needed to resolve how skeletal δ¹³C values vary at intermediate levels of irradiance and zooplankton, and in other coral species.