If you visited a Caribbean coral reef any time over the last few thousand years up until the early 1980s, you would have seen vast forests of branching elkhorn and staghorn corals, Acropora palmata and Acropora cervicornis. I have very clear memories of snorkeling over vast golden landscapes of coral in the Florida Keys with my family in the 1970s. In some places, huge staghorn colonies would reach up from 3-5 meters below, nearly up to the surface.
All that is gone. Both species were nearly wiped out by white band disease in the 1980s. During the outbreak, mortality was very high, probably greater than 95%. In many places both species nearly or actually became locally extinct. The result was a rapid, severe loss of coral cover on reefs throughout the region. The loss of these two dominant reef-builders had countless cascading effects on community inhabitants and ecosystem functioning. Imagine the impact of loosing all the dominant trees across a vast forested region.
Elkhorn and staghorn corals are currently listed as threatened under the US Endangered Species Act and as critically endangered under the IUCN Red List criteria. The pathogen of a very similar, more recent, and probably synonymous disease, white band type II, is thought to be a Vibrio bacteria (Gil-Agudelo et al. 2006). But nobody knows what factors triggered the white band outbreak of the 1980s. I doubt it was temperature, since this was a relatively cool period in the Caribbean (Barton and Casey 2005). And given the regional scale of the epizootic – and the fact that isolated, pristine reefs were hit just as hard as reefs adjacent to urban and agricultural centers – we know nutrient pollution didn’t play a role.
But there are signs of hope. In some places, small populations are beginning to recover. And a very interesting paper published last week in the online, open access journal PLoS One (Vollmer and Kline 2008) has identified several genotypes of A. cervicornis that appear to be totally resistant to white band disease.
The research demonstrates clearly that staghorn corals have the innate ability to resist and recover from the disease that put them on the endangered species list. Interestingly, our study also revealed a huge range of phenotypic variation in disease resistance, from highly resistant genotypes to colonies that nearly always contract the disease when exposed to it. – Dr. Steve Vollmer, lead author and Assistant Professor at Northeastern University’s Marine Science Center.
William Precht, a restoration specialist for the Florida Keys National Marine Sanctuary who is charged with overseeing the restoration of A. cervicornis added; “This is an outstanding study that has broad application to coral reef managers especially those involved in active restoration programs. In addition, with the recent listing of this coral under the US ESA – this study will contribute significantly to the recovery plan that is being developed for this species.”
Barton AD, Casey KS (2005) Climatological context for large-scale coral bleaching. Coral Reefs 24: 536-554
Gil-Agudelo DL, Smith GW, Weil E (2006) The white band disease type II pathogen in Puerto Rico. International Journal of Tropical Biology and Conservation 54: 59-67
Vollmer SV, Kline DI (2008) Natural Disease Resistance in Threatened Staghorn Corals. PLoS ONE 3(11): e3718 doi:10.1371/journal.pone.0003718