Effects of the alga Turbinaria ornata on the growth of the coral Pocillopora verrucosa

Coral reef decline throughout the world is partly due to sedimentation, environmental and anthropogenic disturbances. Increased nutrients have lead to shifts from coral-dominated to algal-dominated coral reefs. Thus it is important to understand the competitive interactions between dominant coral and algal species.  In the lagoons of Moorea, French Polynesia the brown macrophyte Turbinaria ornata and the branching coral Pocillopora verrucosa are both dominant species. We hypothesized that T. ornata negatively affects coral growth due to abrasion, shading, and allelochemicals, but also noted the possible positive effect of protection from corallivores. To determine the effects of T. ornata on the growth of juvenile P. verrucosa, we tested the interaction between these two species by outplanting corals in six manipulative treatments: control (with no T. ornata), corals in the presence of plastic algal mimics, half caged corals, half cage control with no T. ornata, full caged corals and full caged corals in the presence of T. ornata. Ten setups were replicated in both high and low flow sites, for a total of 20 setups (n=60 corals), and growth of the corals was measured by weighing corals at the beginning and end of 29 days. There was no significant difference in coral growth among any treatments. However, results suggest a trend in which corals in the absence of T. ornata demonstrate lower growth rates than corals in the presence of T. ornata. In conclusion, further studies are needed to clarify the effects of T. ornata on corals.