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No Place Like Home for Fish

Research projects into fish in two different oceans have come up with similar results - coral reef fish often spend their life close to home, rather than drifting in the open ocean. The studies were conducted on reefs near St. Croix in the U.S. Virgin Islands, and off the coast of Australia. Both studies discovered that significant numbers of larval fish return to the reefs where they were spawned.

Robert Warner, a biology professor at the University of California, Santa Barbara who oversaw the Virgin Islands study, said "These are the first numbers we've ever had on this. To manage and conserve any marine population, we must know the fate of the young produced by that population, and we must know something about the sources of young recruiting to that population."

The Virgin Islands study was initiated by first author Steve Swearer. The study came out of his questioning of the prevailing view that individual larval fish settling to reefs were most likely spawned elsewhere. Previous researchers have assumed that after a 50-day planktonic larval duration, larvae would have been swept tens or hundreds of kilometers downstream

"This was my approach to challenging that hypothesis," said Swearer, who chose to focus on a well-studied coral reef fish called the bluehead wrasse in three different locations on the reefs of St. Croix.

"The basic paradigm didn't make sense to me. If a larva develops out in the open ocean and disperses away from the natal population, it's at great risk of not finding suitable adult habitat at the end of the larval phase. If you leave an isolated environment like an island, what's the likelihood that you will encounter another coral reef habitat?".

The authors want to see their data used in developing strategies for marine conservation and protection of biodiversity. "If we continue to assume that recruitment comes from non-local reproduction, when in reality local adults contribute significantly to local recruitment, then we run the risk of over-harvesting, whittling away at the population of parents," said Swearer.

The growing interest in developing marine reserves must be based on the latest scientific knowledge, he said. "If we want to be effective in determining optimal placement of marine reserves, as well as evaluating the capability of reserves to sustain exploited stocks, we need to have some empirical techniques that allow us to evaluate the level of connectivity among populations of marine organisms."