Effects of Nutrient Enrichment and Water Quality on Coral Disease Prevalence in Bonaire, Dutch Caribbean

Trying to understand the extent to which anthropogenic stressors impact coral reefs globally has led to an increase in studies which analyze the effects of nutrient enrichment on the frequency and severity of coral disease. Bonaire, Dutch Caribbean currently has no sewage treatment facility in place, resulting in the percolation of wastewater to the surrounding coastal marine environment. On the reefs near resorts, there is a large volume of groundwater used and subsequently discharged into the ocean. As a result, the reefs directly in front of major resorts are likely to have higher disease levels than reefs without resorts nearby. The goal of this study was to evaluate the difference in prevalence of coral disease between sites located in close proximity to groundwater discharge and sites located further away. In order to achieve this objective, six sites with varying gradients of exposure to sewage discharge were surveyed by laying down 1 m x 30 m transect belts parallel to the shore at 6 m, 12 m and 18 m depths. During each survey, nutrient enrichment, macroalgal cover, water depth and coral colonies displaying signs of disease were recorded. Water quality was assessed using a number of parameters including nutrients (ammonium, ammonia, phosphate and dissolved oxygen), Enterococci bacteria and sedimentation. At sites closer to resorts there were higher nutrient levels and percent cover macroalgae, however sedimentation rates and mean percent coral disease frequency were highest at medium impacted sites. Low impacted sites had a greater presence of coral disease at shallower depths, compared to high impacted sites. This data will be used to illustrate a relationship between coral disease and anthropogenic stressors and provide a baseline for future studies.

This student research was retrieved from Physis: Journal of Marine Science IX (Spring 2011)19: 1-11 from CIEE Bonaire.

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