Larger predators key to prey population control, ecological balance

"Once a reserve is established, once the animals are big, it is highly likely that kelp beds will be much more resistant to the formation of urchin barrens," said researcher Robert Warner.
By Brooks Hays   |   Jan. 25, 2017 at 3:28 PM
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Jan. 25 (UPI) -- The health of kelp forests off the coast of California are dependent on the presence of large predators. As new research revealed, large California sheephead, Semicossyphus pulcher, keep urchin populations in check and maintain harmony in the kelp forest ecosystem.

Biologists at the University of California, Santa Barbara found an overabundance of sea urchins diminished productivity and biodiversity among vulnerable kelp forests. By eating large sea urchins, large sheephead help kelp forests rejuvinate.

California sheephead are a colorful wrasse species native to the eastern Pacific Ocean. The fish's strong jaw and teeth, plus a bone called a "throat plate," help the species safely chew and swallow shellfish.

"We found a lot more sheephead within the marine reserves at Catalina Island, which was our primary area of study," Robert Warner, a research professor in UCSB's Department of Ecology, Evolution and Marine Biology, explained in a news release. "Particularly striking was how many more there were in terms of the larger individuals. Those are the ones we actually observed eating urchins of various sizes."

Researchers set up feeding experiments both inside and outside of the marine reserves, and watched the sheephead consume urchins. Scientists found the smallest sheephead were unable to eat urchins. Only fish over a foot in length could consume the spiny sea creatures, and only the biggest sheephead could handle the largest urchins.

In a paper on their experiments, published this week in the journal Proceedings of the Royal Society B, scientists suggest conservation efforts should work to protect the largest fish specimens. Because so much emphasis is put on growing the populations of vulnerable species, fishing regulations often encourage the taking of older, bigger fish, rather than younger specimens. Such an approach ignores the ecological importance of bigger predators.

New strategies are requires, researchers argue.

"One way to restore size structure is to not kill them," Warner said. "And one way not to kill them is to set up reserves. Once a reserve is established, once the animals are big, it is highly likely that kelp beds will be much more resistant to the formation of urchin barrens, which makes it easier for kelp forests to flourish. But that doesn't happen right away. We have to wait for individual predators to get large enough to handle the largest prey."

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