Alterations in dimethylsulfoniopropionate (DMSP) levels in the coral Montastraea franksi in response to copper exposure

Symbiotic corals routinely experience hyperoxic conditions within their tissues due to the photosynthesis of the endosymbiotic dinoflagellate microalgae (Symbiodinium spp.). Symbiodinium spp. produce high intracellular levels of the osmolyte dimethylsulfoniopropionate (DMSP). It has recently been discovered in marine algae that DMSP and its enzymatic breakdown products also play a significant role in the scavenging of cellular reactive oxygen species (ROS). To examine this potential for DMSP in corals, we exposed the hard coral Montastraea franksi to 1, 10 and 50 μg L−1 (ppb) concentrations of the oxidative stressor, copper. Levels of total (DMSPt, all coral tissue) were higher than particulate DMSPp (algal component only), demonstrating partitioning of DMSP between algal symbionts and coral host. Significant changes in levels of DMSPt and DMSPp occurred in M. franksi after 48 h, demonstrating a response to copper and indicating a potential antioxidant role for DMSP. DMSPt and DMSPp levels decreased with copper dose, although at the highest copper dose DMSPp levels increased, whereas DMSPt levels did not. This observed differential response to copper between DMSPt and DMSPp demonstrates that physiological changes may be overlooked if conclusions are based upon DMSPt levels alone, which is a common measure used in coral studies. Decreases in chlorophyll a and algal cell numbers in response to elevated copper were also observed. These indices are important physiological indicators and are often used as indices to normalize DMSP levels. Our data suggest that the use of these common indices for normalizing DMSP may not always be appropriate.