Plague, rabies, Lyme disease, bird flu and swine flu—people seem much more at risk for diseases from animals than the other way around. But it does go the other way too, and it has been discovered that such a case is responsible for a disease that has devastated coral reefs in the Caribbean.
“White pox disease” in coral is caused by a human strain of the common intestinal bacterium Serratia marcescens, which causes the hospital infection serratiosis. (Hospital infections, or nosocomial infections, happen because individuals already in poor health are exposed to pathogens by poor sanitary practices and invasive procedures such as surgery or catheterization.) [Etymological notes on scientific names are at the end of the post.]
The only coral known to be affected is Elkhorn coral (Acropora palmata), a major reef-bulding species in the Caribbean. Healthy Elkhorn coral looks like this.
Here’s an example of Elkhorn coral infected with White pox disease.
A research team at the University of Georgia was recently awarded a $5M grant to investigate the disease in coral, which is “the first known case of such a ‘reverse zoonosis’ that involves the transmission of a human pathogen to a marine invertebrate”. Even more remarkable, in the words of James W. Porter, associate dean of the Odum School of Ecology and the team’s leader, “This bacterium has jumped from vertebrate to invertebrate, from terrestrial to marine, and from anaerobic to aerobic environments. Triple jumps like this are rare.”
The scope of the team’s research will extend beyond gaining an
understanding of the impact of white pox disease on elkhorn coral and
how to counter it. The most likely source of the pathogen for coral
reefs is under-treated human sewage, so the study will also explore
the intersection of public health practices and environmental health
“This investigation addresses not only environmental protection, but
also the socio-ecological determinants of coastal zone protection,”
said Porter. “This includes the cost of wastewater treatment
infrastructure. Given a reliance on tourism by most Caribbean
countries, this study addresses a disease system that is of great
economic importance and public health concern to developing nations.”
“This is science in action to save an endangered species and a threatened ecosystem,” said team leader Porter. “We are linking good public health practices to effective environmental protection.”
Elkhorn and Staghorn coral (Acroporis cervicornis) are both on the US Federal list of threatened species, and in 2008 the National Oceanic and Atmospheric Administration extended additional protection rules usually reserved for endangered species. The new rule will “prohibit the importing, exporting and taking of elkhorn and staghorn corals. Additionally, the rule prohibits any activities that result in the corals’ mortality or injury. Anchoring, grounding a vessel or dragging gear on the species is prohibited. Additionally, damaging the species’ habitat and discharging any pollutant or contaminant that harms the species violates NOAA’s new rule. The rule applies to elkhorn and staghorn coral in the Virgin Islands, Puerto Rico and Florida.” Of course the enforcement will be difficult, but it appears that it’s none too soon to reverse the decline of these reef-building species.
A recent analysis of 500 surveys of 200 reefs showed the most complex types of reef had been virtually wiped out across the entire Caribbean. What survives are mostly “flattened” reefs which provide poor habitat for fish including commercial species, and are less “effective in protecting coastal homes and villages from storm swells and tidal surges”.
Healthy reef of staghorn coral in the Caribbean, below.
When the branched corals are killed off, low-growing corals may take their place but don’t create the rich three-dimensional habitat that the branched ones do. Algae also may increase and blanket surfaces, preventing coral growth.
Source. Photo by Jennifer E. Smith.
Other threats to coral reefs
Coral-building animals live symbiotically with algae. Influenced by water that is too warm or cold, the corals will “expel the algae (zooxanthellae) living in their tissues causing the coral to turn completely white. This is called coral bleaching. When a coral bleaches, it is not dead. Corals can survive a bleaching event, but they are under more stress and are subject to mortality.” Rising ocean temperatures have caused wide-spread bleaching events. Warm waters also absorb more CO2, causing the water to become more acidic and that makes it more difficult for reef-building organisms to form the calcium carbon skeletons that serve as their structural basis.
Overfishing, pollution including sewage and agricultural runoff, dredging,hurricanes, and development have all damaged coral reefs. Each new injury reduces the ability of living organisms to reproduce and to withstand further assaults.
Coral reefs are among the world’s richest ecosystems, second only to tropical rain forests in plant and animal diversity. They arfe essential to fisheries, tourism, and protecting beaches from erosion. Yet “nearly two-thirds of the Caribbean’s coral reefs are threatened by human activities. Agricultural runoff, overfishing, dredging, sewage discharge (a factor in White pox disease), and the growing pace of coastal development have already degraded important reef systems, resulting not only in a tremendous loss of biodiversity but also lost revenue from declining tourism and fishing, and increased coastal erosion.” This last statement comes from the World Resources Institute, which is active many environmental fronts and is currently sponsoring a country-by-country survey of the economic values of Caribbean coral reefs and mangroves: “Supporting the sustainable management of coral reefs and mangroves by quantifying their economic value”.
More about coral reefs
Serratia marcescens was discovered in 1819 by Venetian pharmacist Bartolomeo Bizio, as the cause of an episode of blood-red discoloration of polenta in the city of Padua. Bizio named the organism four years later in honor of Serafino Serrati, a physicist who developed an early steamboat; the epithet marcescens (Latin for “decaying”) was chosen because of the pigment’s rapid deterioration. [Wikipedia]
Acropora palmata: Acropora from the Greek, akros (high) and poros (opening, pore); palmata handlike, from Greek palma (a palm, flat hand; palm branch).
Acropora cervicornis: Acropora as above; cervicornis from the Latin cervus (deer) and cornu (horn, antler)