The Sixth Extinction: An Unnatural History

by Elizabeth Kolbert

The roster of perils includes, but is not limited to: overfishing, which promotes the growth of algae that compete with corals; agricultural runoff, which also encourages algae growth; deforestation, which leads to siltation and reduces water clarity; and dynamite fishing, whose destructive potential would seem to be self-explanatory. All of these stresses make corals susceptible to pathogens. White-band disease is a bacterial infection that, as the name suggests, produces a band of white necrotic tissue. It afflicts two species of Caribbean coral, Acropora palmata (commonly known as elkhorn coral) and Acropora cervicornis (staghorn coral), which until recently were the dominant reef builders in the region. The disease has so ravaged the two species that both are now listed as “critically endangered” by the International Union for Conservation of Nature. Meanwhile coral cover in the Caribbean has in recent decades declined by close to eighty percent.