Oysters And Crabs ‘Stuck In The Middle’

May 12, 2014

By Angela Herring, Northeastern University

Northeastern University ecologist David Kimbro claims to have watched a lot of TV growing up, particularly The Brady Bunch. “You could kind of get a flavor for how an episode was going to turn out based on how Jan or Peter were faring—you know, the middle kids,” said Kimbro, an assistant professor in the Department of Marine and Environmental Sciences.

He and his colleagues—associate professor Jon Grabowski and assistant professor Randall Hughes, ecology experts with labs at Northeastern’s Marine Science Center—think a similar pattern shows up in oyster reefs, where the behavior of the “middle child” in the predator-​​prey food chain plays a strong role in determining how the reef as a whole will fare. New research from the team, published online on Tuesday in the journal Ecology Letters, gives that hunch even more support.

The work complicates the evolution of a paradigm that has pervaded ecology since the 1960s, namely that the species at the top of the food web dic­ate the welfare of the entire system simply by eating.

For instance, observations in the Aleutian Islands in the 1970s showed that when sea otters were doing well, the nearby kelp forests below the ocean’s surface also thrived. This was due, theory said, to the fact that the otters’ feeding patterns naturally managed the sea urchin population, which feeds on kelp.

Fast-​​forward four decades and one sees a large body of evidence indicating that predators do more than eat; they frighten too. In the early 2000s, Grabowski showed that having a predatory fish scare the middle child has the same effect as predation itself. Like­wise with the sea otters—just swimming around scares the urchins enough to send them into hiding and stop eating kelp.

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