Scleractinian coral diseases in south Florida and Dominica (West Indies): Epizootiology and effects on host tissue structure and reproduction

Coral diseases are contributing to the decline of coral reefs worldwide and have been demonstrated to effect changes in community structure and diversity. This study focused on the spatial and temporal dynamics of coral diseases (black band disease (BBD), white plague (WP), dark spots syndrome (DSS) and white band disease (WBD)) in south Florida and Dominica (West Indies), as well as the examination of the effects of diseases on coral reproductive activity, total lipid content, and tissue and cellular structure. Transmission electron microscopy was utilized to examine the ultrastructural anomalies associated with BBD and WP type II, which included the degeneration of endosymbiotic algae, membrane disruption, karyolysis, an increase in the density of mucus secretory cells, the loss of flagellar structures, and liquefactive necrosis. Ultrastructural changes unique to BBD infections (swollen mitochondria, swollen microvilli and cilia, and the degeneration of the mesoglea) were indicative of hypoxia and toxin (sulfide) related tissue death. A histological examination of DSS demonstrated that this condition may be caused by the invasion of the coral calicoblastic epithelium by endolithic fungi when the coral is stressed. WP had significant negative impacts on the reproductive activity of Montastraea faveolata. However, these effects were localized to the region of tissue directly impacted by the WP disease band/lesion. In both south Florida and Dominica, DSS was the most common syndrome, but BBD and WP caused the largest amount of coral tissue death. The only disease that exhibited a linear increase in incidence with elevated temperature was BBD. However, WP and WBD were most active during the warmest survey months. In most cases, disease progression rates were noted to increase with warmer water temperatures. DSS and BBD were the most persistent conditions, while WP infections were comparatively short-lived (approx. 1–3 months). Disease density (WP and DSS) at each site was significantly, positively correlated with the relative frequency of target species. The species noted to be most susceptible to WP and BBD varied in each survey year. Coral diseases predominantly affected the larger colonies of most susceptible species, and the re-infection rates of colonies between survey years was approximately 25%. Scleractinian recruitment rates (onto areas of the skeleton exposed via disease-related mortality) were low, and the comparatively high occurrence of algae may result in a shift towards algal-dominated reefs.