Kathryn P. Sutherland , and James W. Porter

The Etiology of White Pox, a Lethal Disease of the Caribbean Elkhorn Coral, Acropora palmata

Kathryn P. Sutherland, and James W. Porter University of Georgia, Athens, GA

Kim B. Ritchie Scripps Institution of Oceanography, La Jolla, CA MicroGenomics, Carlsbad, CA

Shawn W. Polson Clemson University, Clemson, SC

Erich Mueller Mote Marine Laboratory, Center for Tropical Research, Summerland Key, FL

Esther C. Peters Tetra Tech, Inc., Fairfax, VA

Deborah L. Santavy Gulf Ecology Division, U.S. EPA, Gulf Breeze, FL

Garriet W. Smith University of South Carolina, Aiken, SC

Epizootics have been reported for several coral species and evidence is mounting of substantial declines in the biodiversity and abundance of reef-building corals. The greatest losses within the Caribbean are among the branching elkhorn and staghorn corals, Acropora palmata and Acropora cervicornis. White pox disease, which exclusively affects A. palmata, was first documented in 1996 on reefs off Key West, Florida and has since been reported on reefs throughout the Caribbean. In Florida, populations of A. palmata are being decimated by white pox. Between 1996 and 1999, the average loss of A. palmata at seven reef sites in the Florida Keys was 85% and at some reefs losses were as high as 98%. These severe population declines of the coral community’s most important primary producer and shallow water framework builder are especially important given the longevity and slow recruitment of this species. We have identified a common fecal enterobacterium, Serratia marcescens, as the causal agent of white pox. This is the first time that a bacterial species associated with the human gut has been shown to be a marine invertebrate pathogen. It is unlikely that the mid-1990’s are the first time that Serratia marcescens entered the tropical marine environment. Additional factors that may contribute to this bacterium’s increased virulence include elevated water temperatures and elevated nutrients, both of which have been documented in EPA’s long-term water quality assessment program in the Florida Keys. In general, increased nutrients and temperatures favor microbial growth, and the disease prognosis for a warmer, more polluted ocean is worrisome.

Coral colonies affected by white pox are characterized by the presence of irregularly shaped distinct white blotches of recently dead coral skeleton surrounded by a necrotic front of normally pigmented living coral tissue. Lesions range in area from a few square centimeters to greater than 80 cm2 and can develop simultaneously on all surfaces of the coral colony. White pox lesions exhibit tissue loss along the perimeter and increase in area as tissue is lost from the leading edge of the infection. The rate of tissue loss is rapid, averaging 2.5 cm2 day-1, and is greatest during periods of seasonally elevated temperature. White pox is highly contagious with nearest neighbors most susceptible to infection. The disease spread rapidly within and between reefs in the Florida Keys during the late 1990s.

Substantial population losses of acroporid corals are changing the composition, structure, and probably function of Caribbean coral reef ecosystems. Acropora palmata, is an important Caribbean shallow water species, providing elevated rates of calcium carbonate deposition and the highly complex three dimensional structure of the shallow water fore reef. Acroporids reproduce almost exclusively by fragmentation. While vegetative reproduction may be well adapted to recolonization following mechanical disturbances such as hurricanes, colony fragmentation is ineffectual following severe population declines due to disease, which frequently kills the entire coral colony. If colonies are too rare or too far apart for high fertilization success, then A. palmata may be experiencing an Allee effect, making rapid recovery of this species in the Florida Keys impossible.

Patterson, K.L., J.W. Porter, K.B. Ritchie, S.W. Polson, E. Mueller, E.C. Peters, D.L. Santavy, and G.W. Smith. 2002. The etiology of white pox, a lethal disease of the Caribbean elkhorn coral, Acropora palmata. Proceedings of the National Academy of Sciences USA 99:8725-8730. Kathryn, Patterson Sutherland, Department of Marine Sciences, University of Georgia, Athens, GA, 30602, Phone: 706-542-3410, Fax: 706-542-6040, [email protected].