Interactions of coral, algae, fish and abiotic factors on a eutrophic fringing reef in Barbados

Abstract. Many coral reefs have experienced worldwide deterioration due to increased anthropogenic disturbance and rising sea temperatures. Regardless of their complexity, fundamental patterns have been characterized. Increases in macroalgae, depth, sedimentation and current have been linked to decline in corals, while herbivorous fish prevent harmful algal overgrowth. To better understand deteriorated reefs, we investigate these associations on two eutrophic fringing reefs near the Bellairs Research Institute in Barbados. Four transects were used to sample three depth zones, where coral and algae were quantified along with fish richness. Sedimentation, current and coral stress are also assessed. Depth was not correlated with coral diversity or percent cover; however, colony height of the coral Porites asteroides colonies was less in shallow waters (F=5.6, p=0.0082). Herbivorous fish correlated with palatable algae at shallow depths (R2=0.213, p=0.015). Further, algae cover was positively correlated with coral diversity at medium depths, against common predictions (R2=0.471, p=0.014). Sedimentation was not a significant predictor. Overall, the depth range may not have been large enough to allow for variation in coral diversity across depths. P. asteroides may be shorter at lower depths to prevent exposure to waves and air. Abiotic conditions favoring algal growth in shallow depths may maximize fish feeding. Finally, at medium depths Porilithon pachydermum a crustose algae, may be facilitating the initial establishment of corals rather than overtaking them. Overall, not all the expected patterns were seen. These differences may represent fundamentally altered patterns in reef ecosystem processes. Documenting these changing interactions across impacted reefs may help further understand their vulnerabilities.