Black Reefs Threaten Coral Diversity in the Line Islands

By Candice Canady,
Marine conservation student

Coral reefs are threatened globally and, without an undisturbed example from which to form a baseline, researchers are hard-pressed to predict how global and local stressors influence them. Luckily, a number of coral reefs exist in the Central and South Pacific that may hold the key to better understanding changes in reef populations worldwide. The Line Islands, located south of Hawaii, are home to some of the most pristine reefs in the world (Knowlton and Jackson 2008). These reefs have high biodiversity and have experienced very little influence from human populations (Barott 2013). However, they are threatened by their own unique set of stressors. The Central Pacific is traditionally an iron-poor region. This lack of iron reduces competition between coral and primary producers, such as algae and cyanobacteria (Martin and Fitzwater 1988). Recent studies have noted phase shifts (shifts from coral-dominated structures to regions dominated by algae) on coral reef atolls throughout the Pacific as a result of iron pollution (Kelly et al. 2012). These areas have been termed “black reefs” due to the dark-colored turf algae that covers the bottom (Barott 2013). A 2012 study by Kelly et al. showed that the black reefs in this area were introduced by shipwrecks that serve as point sources of iron pollution, causing algal and bacterial blooms that kill the natural coral reef structure.

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