How does water quality correlate with coral disease, bleaching, and macroalgal growth on coastal reefs? A comparative study of various anthropogenic threats on Bonaire, N.A.

Coral reefs worldwide are currently jeopardized by anthropogenic factors such as land-based pollution, coastal development, and sediment erosion. In the Caribbean alone, nearly two-thirds of coral reefs have been deemed as threatened. This study investigated the potential negative effects of water quality and eutrophication, Enterococci bacteria (found in human gut), and sedimentation on coral disease, bleaching, and macroalgal growth on the near shore reefs of Bonaire, N.A. Monitoring sites were defined according to their proximity to anthropogenic activity: “more impacted” or “less impacted” (< 200 m and > 200 m from coastal development, respectively). Water samples at 5 m were collected weekly and at 12 m biweekly from each site and tested for nutrient concentrations (NO3, NO2 - , NH4-N, PO4), Most Probable Number of Enterococci bacteria, sedimentation rates, and particle size distributions. Video transects (100 m) were also taken at defined depths and analyzed for live coral cover and diversity, percent disease and bleaching, and macroalgal cover. Data showed elevated NH4-N levels at all sites, Enterococci bacteria present at 3 of the 4 sites (mainly at 5 m), and sediment particle counts showed significant differences among sizes at both depths and between the interaction of size and impact at 12 m. There was also a strong trend of finer grained sediments at high impact sites and coarser grained sediments at low impact sites. Very little overall coral disease (1.105 ± 1.563 % at more impacted sites and 0.400 ± 0.566 % at less impacted sites in 12 m) and bleaching (3.245 ± 0.615 % at more impacted sites and 1.390 ± 1.966 % at less impacted sites in 12 m) was found on the reefs however, neither were present at 5 m. There was significantly more macroalgae at 12 m and a strong trend of more macroalgae at the deeper, more impacted sites. This study suggests that increased anthropogenic activity on Bonaire is contributing to the increased NH4- N levels, Enterococci bacteria presence, and finer particle sediments, which future studies may correlate significant interactions between these parameters and coral disease, bleaching, and macroalgal growth.

This student research was retrieved from Physis: Journal of Marine Science VI (Fall 2009)19: 35-43 from CIEE Bonaire.

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