Clown anemonefish lay their eggs on bare rocks, which are tended by the parents for several days.
After hatching, the free-swimming larvae typically settle down near sea anemones after just 11 days, making the fishes' stay-at-home tendency not particularly surprising.
(Read "No Nemo: Anemones, Not Parents, Protect Clownfish" [June 5, 2003].)
The untended eggs and larvae of vagabond butterflyfish, on the other hand, may spend four to six weeks drifting with the currents—a trait shared by many commercially important fish species.
Right now little is known about how far the butterflyfish larvae travel and how the juveniles find their way back to their parents' reef, Almany said.
"We can only guess about how they might locate the exact reef on which they were born," he said. "Perhaps some form of imprinting, such as a chemical 'memory' of home."
Not Reseeding Reefs?
Robert Steneck is a marine ecologist at the University of Maine who was not involved in the study.
He noted that previous studies had often assumed high rates of dispersal in coral reef fish, with local populations maintained by young fish arriving from across a broad region.
Similarly, the theory behind many marine reserves is that the offspring of fish in protected areas will help maintain populations far beyond reserve boundaries.
Almany's team, Steneck said, "found the best coral reef system, the best marking tool, and the right species of fish to empirically test the theories. Their results were very surprising but very important indeed."
The finding that fish populations on coral reefs may largely be locally generated means the benefits of reserves may not extend as far as had been hoped.
"The stated goal of many [marine] reserves is that they can be a source of larvae for effectively reseeding damaged reefs downstream," Steneck said.
"We might want to increase our efforts to protect reproducing fish outside of reserves," he continued, "if we don't want to see growing dead zones throughout the world's reefs."
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