An Investigation into the Effect of a Marine Protected Area on the Juvenile Coral Densities and Communities Around St. Croix and Buck Island Reef National Monument, U.S. Virgin Islands

Wright, William

This study tests the effects of marine protected areas on coral recruitment. It also relates the substrate composition, topography and grazer abundance to the protected area. The dissertation includes background information on coral reef ecology in The U.S. Virgin Islands (St. Croix and St. John), methods, results, discussion, conclusion and references. The density and community structure of juvenile corals were examined at depths from 0.5m to 4m on the reefs of St. Croix, Buck Island Reef National Monument (BIRNM) and St. John (U.S. Virgin Islands), to see if a no fishing policy indirectly enhanced juvenile coral recruitment. The substrate composition, topography, and the grazing pressure were also recorded to test for associations with the juvenile coral density and community composition. There was no significant difference in the mean density of juvenile corals inside and outside a marine protected area (BIRNM, Marine Garden), even though the area had been protected for over 30 years. The study also showed that there was no significant difference in the substrate composition or the topography between these two areas. There was however significantly different densities of urchins, higher outside the BIRNM, Marine Garden and triggerfish, higher inside the BIRNM, Marine Garden. There was also evidence to support a strong preditator/prey relationship between triggerfish and urchin densities. The diversity of fish species was also found to be significantly higher inside the BIRNM, Marine Garden, indicating a more stable and robust fish community, that is less likely to suffer from changing environmental conditions. The study also showed that the percentage cover of rock had a significant positive relationship with the density of juvenile corals and was the best single predictor, and that a combination of rock and algae >5cm was the best combined predictor. With algae >5cm having an inhibitory effect on juvenile coral densities. The density of grazers did not seem to have a direct relationship with the density of juvenile corals. Juvenile coral community analysis showed that there was no significant difference in the communities inside and outside the BIRNM, Marine Garden, or those found in different reef zones. The study also suggested that there might be a relationship between parrotfish densities and juvenile coral communities although this was not proved. The main conclusions that can be drawn from this project are that the creation of a marine protected area did not have a significant affect on juvenile coral densities. Thus if active management practices cannot enhance recruitment, they should concentrate on protecting the new recruits as well as the corals already present. Since post-recruitment mortality may be the most important factor controlling adult community structure. This project also suggests that the amount of rock is important in successful coral recruitment, and thus grazing, which creates areas of rock must also be important.