Ocean Sentry
(From sciencedaily.com) – Shipwrecks on coral reefs may increase invasion of unwanted species, according to a recent U.S. Geological Survey study. These unwanted species can completely overtake the reef and eliminate all the native coral, dramatically decreasing the diversity of marine organisms on the reef.
This study documents for the first time that a rapid change in the dominant biota on a coral reef is unambiguously associated with man-made structures.
The findings of the study suggest that removal of these structures sooner rather than later is key to keeping reefs healthy.
In many areas of the world, coral reef health is declining, but identifying the exact cause of the problem is difficult. Overgrowth of coral reefs by other species, such as algae, are usually attributed to environmental degradation, but bleaching, disease, damage by typhoons, overfishing, coastal development, pollution, and tourism can cause problems as well.
The study was conducted at Palmyra Atoll National Wildlife Refuge in the central Pacific, a relatively remote, comparatively pristine area where little human activity has occurred since WWII. In 1991, a 100-foot vessel shipwrecked on the atoll. Scientists first surveyed the area in 2004 and found a species called Rhodactis howesii —an organism related to sea anemones and corals—in low abundance around the wreck. In subsequent years, however, populations of this organism increased exponentially. Scientists documented extremely high densities of R. howesii that progressively decreased with distance from the ship, whereas R. howesii were rare to absent in other parts of the atoll. They also confirmed high densities of R. howesii around several buoys.
Whether this phenomenon occurs on other coral atolls is unknown; however, in the case of Palmyra, the R. howesii infestation is beginning to reach catastrophic proportions, according to Dr. Thierry Work, the lead author of the study and a scientist at the USGS National Wildlife Health Center, Honolulu Field Station. Within a few years, R. howesii spread to where it now occupies nearly 1 square mile.
