Incidence of Bleaching and Disease in Hermatypic Scleractinian Corals of Biscayne National Park

Zimmer, Beth

The world's coral reefs generate large sums of income and provide a habitat for a wealth of diverse species, making them valuable economic and biological resources. Due to recent increases in the frequency of coral bleaching and disease, concern has developed over the health of coral reef ecosystems. This thesis had two objectives: (1) to determine whether mass bleaching events in the Florida Keys during the 1990's were related to high sea surface temperatures and (2) to establish baseline coral health and disease levels on the reefs ofBiscayne National Park. To determine whether the bleaching events were temperature related, known bleaching years were compared with both annual maximum temperatures and the annual number ofbleaching index days. No statistically significant associations between elevated temperature and bleaching years were determined. However, a general trend was observed between bleaching events and an increased number ofbleaching index days. Reef surveys were conducted to establish the current levels of coral diseases and the general health of scleractinian corals of Biscayne National Park. The disease frequencies were variable among the reef sites, ranging from 0.0% to 3.7% infection. Two diseases were detected in the surveys: White Band Disease which was present in approximately 0.35% of surveyed colonies and Yellow Blotch Disease which had infected 1.1% of surveyed corals. Both diseases were most frequent inMontastrea spp., which may suggest a reduced resistance to infection. The greater frequency of disease on the patch reefs of the carbonate platform, versus the barrier-bank reefs on the edge of the platform, was statistically significant and may be due to the greater volume of Hawk Channel water bathing the patch reefs. A majority of surveyed colonies were classified as healthy, although a considerable percentage (26.0%) exhibited signs of moderate to severe coral stress. Although only a small percentage (2.0%) of colonies were bleached, Agaricia agaricites composed 32.4% ofthese colonies. Approximately 3.3% of the surveyed colonies exhibited pale coloration (partial bleaching). These data will serve as baseline health and disease levels which may be used for comparison with future studies .