The orange cup coral, Tubastraea coccinea, was introduced into the Caribbean in the 1930s from the Indo-Pacific.  Since then, it has spread throughout the Caribbean and into the near-shore reefs of Bonaire.  In this study, we assessed the interaction of this exotic coral with the native reef community.  We hypothesized that the three-dimensional structure of T. coccinea facilitates native species among which it successfully grows by providing habitat and food.  To investigate this, colonies of T. coccinea were monitored in the field over several morning, noon, and evening sessions to capture how native species naturally interact with the coral.  Colonies of the coral were also collected, defaunated, and experimentally caged-off so that consumers would not be able to graze from their surfaces and compared with open cage controls.  Percent cover of cyanobacteria and macroalgae growing on the corals was monitored over the 21 day duration of the study.  Species richness within open and closed cages was also measured to assess which native species utilized the habitat as well as the biofilm and algae that grow on the surfaces of the coral.    

Results/Conclusions

Cyanobacterial percent cover changed over the duration of the study as well as differed between experimental treatments, increasing to 18% and decreasing to 3% in closed cages versus increasing to 9% and decreasing to 1% in open cages between days 10 and 21.  The percent cover of macroalgae in closed cages was significantly higher than in partially closed cages (45% and 25%, respectively) by day 21.  This was likely due to the exclusion of native herbivores from the fully closed cages.  Native species richness within both caging treatments increased throughout the study, but showed a 4-fold increase (from 2 to 8 species) within closed cages between days 5 and 10 versus a leveling-out (3 species) in open cages.  A variety of native fishes, crabs, gastropods, and annelids were observed in both natural and experimental settings utilizing T. coccinea as habitat and/or a food source.  These interactions between native and non-native species suggest that the coral is positively interacting within the ecosystem it has successfully invaded and has become a facilitator of native species.