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Shipwrecks on coral reefs harbor unwanted species
August 20, 2008Shipwrecks 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, published in the open-access journal PLoS ONE, 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.
"Why this phenomenon is occurring remains a mystery," said Work. One possibility, he said, is that iron leaching from the ship and mooring buoy chains, accompanied with other environmental factors particular to Palmyra atoll, are somehow promoting the growth of Rhodactis.
"Given the ability of Rhodactis sp. to rapidly reproduce and completely smother reefs, managers are now facing the possibility that even with removal of the ship, sheer reproductive capacity of R. howesii may continue to fuel its spread along the western reef shelf of Palmyra," Work said.
Understanding what constitutes a healthy underwater ecosystem, as well as what does not, is crucial to preventing further losses in species and habitat. This research illustrates a little-known problem that, unlike global warming and pollution, could be prevented by removing man-made debris such as shipwrecks from coral reefs before organisms like Rhodactis howesii can overtake healthy coral reefs.
Public Library of Science
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.
"Why this phenomenon is occurring remains a mystery," said Work. One possibility, he said, is that iron leaching from the ship and mooring buoy chains, accompanied with other environmental factors particular to Palmyra atoll, are somehow promoting the growth of Rhodactis.
"Given the ability of Rhodactis sp. to rapidly reproduce and completely smother reefs, managers are now facing the possibility that even with removal of the ship, sheer reproductive capacity of R. howesii may continue to fuel its spread along the western reef shelf of Palmyra," Work said.
Understanding what constitutes a healthy underwater ecosystem, as well as what does not, is crucial to preventing further losses in species and habitat. This research illustrates a little-known problem that, unlike global warming and pollution, could be prevented by removing man-made debris such as shipwrecks from coral reefs before organisms like Rhodactis howesii can overtake healthy coral reefs.
Public Library of Science
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Urgent action on international coral reef crisis
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Coral reefs found growing in cold, deep ocean
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Smithsonian perspective: Biodiversity in a warmer world
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Diversity of plant-eating fishes may be key to recovery of coral reefs
For endangered coral reefs, not all plant-eating fish are created equal. A report scheduled to be published this week in the early edition of the journal Proceedings of the National Academy of Sciences suggests that maintaining the proper balance of herbivorous fishes may be critical to restoring coral reefs, which are declining dramatically worldwide.
Extinction by asteroid a rarity
In geology as in cancer research, the silver bullet theory always gets the headlines and nearly always turns out to be wrong.
Modest CO2 cutbacks may be too little, too late for coral reefs
How much carbon dioxide is too much? According to United Nations Framework Convention on Climate Change (UNFCCC) greenhouse gases in the atmosphere need to be stabilized at levels low enough to "prevent dangerous anthropogenic interference with the climate system." But scientists have come to realize that an even more acute danger than climate change is lurking in the world's oceans-one that is likely to be triggered by CO2 levels that are modest by climate standards.
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