Coral reefs are experiencing rapid declines from deteriorating environmental conditions across the globe. Recent reports indicate that 58–70% of coral reefs worldwide are directly threatened by human-associated activities, while over 80% of the Caribbean coral-reef cover has disappeared in the last 30 years. Coral reef communities experiencing persistent environmental disturbances (e.g., coastal development and land-based pollution) are undergoing changes that lead to a loss of coral diversity, increased incidence of disease, reduced growth, reduced reproduction, and mass mortality. From 1996-2000, a time span that included a major El Niño event, corals in the Florida Keys National Marine Sanctuary lost a record 38% of their living coral cover. For some of the majors reefs in the Florida Keys, there has been utter decimation beginning after 1975 (Fig. 1). The causes of these devastating declines, however, remain largely unknown.
The primary question facing resource managers is whether coral declines result from climatic forces, local or regional anthropogenic factors, or the synergistic effects of these different forces. If declines are caused solely by global factors, there may be little resource managers can do to immediately ameliorate the problem. However, if local (defined as a restricted region of about 50 kilometers) factors contribute to coral declines, resource managers may be able to respond with mitigation efforts. For example, if urban effluent is the principle stressor, discharges can be managed and regulated. Unfortunately, conventional coral monitoring and mapping protocols have had limited success in demonstrating the causes of coral reef declines in the Florida Keys and elsewhere. Most monitoring programs were designed to establish baseline conditions and determine trends, not to identify sources of stress. The inability of coral monitoring programs to pinpoint factors affecting local reef declines makes it difficult for resource managers to effectively manage coral reefs.
We have been investigating the Florida Keys since 1999. Our work in 1999 demonstrated that oxidative stress was a significant factor in seasonal coral bleaching, and that the inherent antioxidant capacity of an individual coral in March was a significant predictor of whether a coral would bleach in September (Fig. 2) . In 2001, populations of the coral, Montastraea annularis, were sampled at four sites near Molasses Reef within the Florida Keys National Marine Sanctuary and one reef within Biscayne National Park on a quarterly basis (Fig. 3). Anecdotal observations showed corals at Alina’s Reef in Biscayne National Park appeared healthy in March, 2000, but experienced an acute loss of coral cover by August, 2000. Lacerationregeneration assay data from these corals throughout 2000 indicated that the corals were severely stressed and unlikely to be reproductive viable for all five locations. Cellular diagnostic analysis indicated that corals from Alina’s Reef were in distress: they had been afflicted with a severe oxidative damaging and protein-denaturing stress, both the coral polyps and their symbiotic zooxanthellae. This condition was associated with a significant pollutant-detoxification response in both species, reflecting probable chemical contaminant exposure (localized/regional stressor; Fig. 4).
In 2001, our group of collaborators was awarded a Marine Biotechnology National SeaGrant award to link ecological processes with cellular and molecular processes (Fig. 5). We sampled a number of other organisms at the same sites we sampled coral, including damsel fish, white grunt fish, and a snail that feeds on coral. Population, community, and ecological-level parameters were also measured at these four sites.
To give a non-coral example of this project, we examined white grunts (fish). Fish sampled from the four different location exhibited very different cellular signatures, but the dominant pathology among all sites was associated with pesticide toxicity (Fig. 6). A majority of the grunts taken from Alina’s Reef had dis-colored, cirrhotic livers. Cellular diagnostic analysis indicated that most of the fish had porphyria, an accumulation of porphyrin species (Fig. 7). Environmental chemistry analysis of the livers showed that these fish were contaminated with 20 different pesticides (Table 1). The highest contaminant in all three populations was DDT, which was higher than the threshold concentrations for safe consumption for wildlife consumers (e.g., fish that subsist on grunts) and humans (National Academy of Sciences, 1973; Environment Canada, 1997; U.S. EPA, 1997). It is unlikely that DDT caused the hepatopathology in fish from Alina’s Reef. Instead, the more likely pesticide to induce this pathology was hexachlorobenzene (HCB); a compound renown for inducing porphyria and cirrhotic livers at body burdens in the low parts per billion range.
Scientific papers published from this effort:
Downs, C.A., J.E., Fauth, J.C. Halas, P. Dustan, J. Bemiss, C.M. Woodley (2002) Oxidative stress and seasonal coral bleaching. Free Radial Biology & Medicine 32: 533-543. Fauth J. E., Downs, C. A., Halas, J. C., Dustan, P., and C.M. Woodley (2003) Mid-range prediction of coral bleaching: a molecular diagnostic system approach. In N. Valette-Silver and D. Scavia, eds. Ecological Forecasting: New Tools for Coastal and Ecosystem Management. NOAA Technical Memorandum NOS NCCOS 1. pp. 5-12.
Downs, C.A., Fauth, J.E., Robinson, C.E., Curry, R., Lanzendorf, B., Halas, J.C., Halas, J., C.M. Woodley (2005). Cellular Diagnostics and Coral Health: Declining Coral Health in the Florida Keys. Marine Pollution Bulletin 51:558-569.
Downs, C.A. J.E. Fauth, D. Wetzel, P. Hallock, J.F. Halas, J.C. Halas, R. Curry, C.M. Woodley (2006). Investigating Coral Reef Degradation at Alina’s Reef in the Florida Keys: Cellular Physiology of White Grunt (Haemulon plumieri) as a Biological Indicator. Environmental Forensic Journal 7:15-32.