Invading is not always bad: A study of positive interactions between the invasive coral Tubastraea coccinea and native reef species of Bonaire, NA
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, I assessed the interaction of this exotic coral with the native reef community. I 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 visually monitored in the field over several the morning (8:00), noon (12:00) and evening (18:00) sessions to capture how native species interact with and use the coral in a natural setting. Colonies of T. coccinea were also collected, defaunated, and experimentally caged-off so that consumers would not be able to graze the biofilm and/or algae growth on the colonies. Percent cover of cyanobacteria and macroalga growing on the corals was monitored over the 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 biofilm and algae. Cyanobacterial percent cover changed significantly over the duration on the study (increasing to 18% and decreasing to 3% in closed and increasing to 10% and decreasing to 1% in open cages ) as well as differed between closed and open cages (18% versus 9% at highest percent cover, respectively). The percent cover of macroalgae in closed cages was significantly higher than in partially closed cages (45% versus 25%, respectively) from day ten to the completion of the study. This was likely due to the exclusion of herbivorous fishes in the closed cages. Native species richness within both cage treatments increased throughout the duration of the experiment, but showed a fourfold increase between day 5 and10 within closed cages versus a leveling-out in open cages. Native fishes and annelids were observed in both the natural and experimental settings utilizing T. coccinea as both a habitat and a food source. These interactions of native species with T. coccinea suggest that the coral is positively interacting with the ecosystem in which it has successfully invade settled in and has become a facilitator of native species.