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Coral reef species forced to go with the flow
It is essential to know what goes with the flow, marine scientists report in the Aug. 17 issue of Nature.
Understanding larval dispersal through ocean currents is crucial in protecting the world's declining coral reefs, said Paul Barber, a National Science Foundation fellow at Harvard University and lead author of the study.
Conventional thinking has held that the larvae of coral reef species drift great distances on ocean currents, supplying new recruits to distant coral reefs, stabilizing existing populations and colonizing new ones.
Resource managers only recently considered these important ecological connections, and empirical data about the nature of larval dispersal between coral reefs is scarce.
Barber examined the larval flow of mantis shrimp populations as a model for several species that live on coral reefs.
"Larval recruitment from nearby or distant coral reefs is thought to be a critical part of the ecology of healthy coral reefs," Barber said. "Little is known about the true nature of larval dispersal between reefs. We are trying to better understand this important process."
The study notes that populations of mantis shrimp on coral reefs in Indonesia show a sharp genetic demarcation over distances as short as 300 to 400 kilometres, despite the powerful currents that flow between the home sites of these creatures.
Barber's research supplements growing evidence that reef species are much less mobile than previously thought.
"We don't understand larval dispersal as well as we think we do, " Barber said.
Barber's work shows that within large ocean provinces there may be a great deal of larval exchange, but that there are areas where that exchange is limited.
"Lots of people believe that if a protected coral reef is fished out, it will essentially come back to life because other larvae will drift in and re-establish the population," Barber said. "As people rehabilitate coral reefs, it is important to know if that will, in fact, happen."
Barber's work suggests the importance of linking marine reserves to one another within an ocean region. In many areas throughout the world, particularly the Indo-West Pacific region, these links are not taken into consideration in marine management.
"You can't treat the whole Indo-West Pacific as a single management area," he said. "If you place all resources in a single reserve and that reserve depends on the influx of larval recruits from somewhere else, if the source of larval production dies off, all of the protection in the world won't do you any good."
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