By Kathryn L. Patterson, James W. Porter, Kim B. Ritchie, Shawn W. Polson, Erich Mueller,Esther C. Peters, Deborah L. Santavy, and Garriet W. SmithPNAS June 25, 2002 99 (13) 8725-8730; https://doi.org/10.1073/pnas.092260099

1. Communicated by Eugene P. Odum, University of Georgia, Athens, GA (received for review December 12, 2001)

Abstract

Populations of the shallow-water Caribbean elkhorn coral, Acropora palmata, are being decimated by white pox disease, with losses of living cover in the Florida Keys typically in excess of 70%. The rate of tissue loss is rapid, averaging 2.5 cm²⋅day⁻¹, and is greatest during periods of seasonally elevated temperature. In Florida, the spread of white pox fits the contagion model, with nearest neighbors most susceptible to infection. In this report, we identify a common fecal enterobacterium, Serratia marcescens, as the causal agent of white pox. This is the first time, to our knowledge, that a bacterial species associated with the human gut has been shown to be a marine invertebrate pathogen.

Epizootics have been reported for several coral species (1–6), and evidence is mounting of substantial declines in the biodiversity and abundance of reef-building corals (7). The greatest losses within the Caribbean are among the branching elkhorn and staghorn corals, Acropora palmata and Acropora cervicornis, for which losses have been documented in St. Croix (8), Belize (9), Jamaica (10–12), Florida (13), and the Bahamas (14). Since the mid-1990s, observations of new coral diseases have been on the rise (1, 6). The Florida Keys National Marine Sanctuary has sustained an ecosystem-wide increase in the number of coral species exhibiting disease as well as the number of reef sites with diseased corals (6). The etiologies and mechanisms of tissue death of the majority of coral diseases are not understood (2), and epidemiological data regarding the losses to coral reef communities due to these diseases are scarce. In this paper, we fulfill Koch’s postulates and describe the etiology of white pox disease. We also quantify substantial population losses suffered by white pox-affected colonies of A. palmata in the Florida Keys.

White pox disease was first documented in 1996 on Eastern Dry Rocks Reef (24° 27.715′ North, 81° 50.801′ West) off Key West, FL (15). The disease has since been observed on reefs throughout the Caribbean (6, 16–18). White pox exclusively affects the elkhorn coral,A. palmata, an important Caribbean shallow water species that provides elevated rates of calcium carbonate deposition (19) and the highly complex three-dimensional structure of the shallow water fore reef. Coral colonies affected by white pox disease are characterized by the presence of irregularly shaped white lesions where tissue has disappeared from the skeleton (Fig. 1). 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. The distinct white patches and the potential for tissue loss everywhere on the coral colony distinguish this disease from white-band disease (8), which develops at the base of a coral branch and progresses upward toward the branch tip in a concentric ring. Disease signs also clearly differ from coral bleaching and predation scars produced by the corallivorous snail,Coralliophila abbreviata (20, 21). Newly bared calcium carbonate skeleton of white pox-affected A. palmata is rapidly colonized by a variety of turf algae.

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Figure 1

White pox disease lesion on A. palmata at Looe Key Reef, FL, August 1998. The square pin (1.61 cm²) was used to calibrate the image tracing software (photograph by K.L.P.).

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