Standing on a promontory, Kevin Lafferty, a marine biologist at the University of California at Santa Barbara, watches the teeming scene and sees another, more compelling drama.
For him, the real drama of the marsh lies beneath the surface in the life of its invisible inhabitants: the parasites.A curlew grabs a clam from its hole."Just got infected," Lafferty
looks at the bank of snails."More than 40 percent of these snails are infected," he
pronounces."They're really just parasites in disguise."He
points to the snowy constellation of bird droppings along the bank.
At the Carpinteria salt marsh, Kevin Lafferty
has been exploring how parasites may shape an entire region's ecology.In a series of exacting experiments, he
has found that a single species of fluke, Euhaplorchis californiensis, journeys through three hosts and plays a critical role in orchestrating the marsh's balance of nature.
set out to answer one main question: Would Carpinteria look the same if there were no flukes?He
began by examining the snail stage of the cycle.The relationship between fluke and snail is not like the one between predator and prey.In a genetic sense, infected snails are dead, because they can no longer reproduce.But they live on, grazing on algae to feed the flukes inside them.That puts them in direct competition with the marsh's uninfected snails.
To see how the contest plays out, Lafferty
put healthy and fluke-infested snails in separate mesh cages at sites around the marsh."The tops were open so the sun could shine through and algae could grow on the bottom," says Lafferty
found was that the uninfected snails grew faster, released far more eggs, and could thrive in far more crowded conditions.The implication: In nature, the parasites were competing so intensely that the healthy snails couldn't reproduce fast enough to take full advantage of the salt marsh.In fact, if flukes were absent from the marsh, the snail population would nearly double.That explosion would ripple out through much of the salt marsh ecosystem, thinning out the carpet of algae and making it easier for the snails' predators, such as crabs, to thrive.Lafferty
then studied the killifish.Initially, he
found little evidence that flukes harmed or changed the fish they colonized; the fish didn't even mount an immune response.But Lafferty
figured that flukes sitting on the brain were in a good position to be doing something.
and Morris followed up with a marsh experiment in which they set up two pens, each filled with 53 uninfected killifish and 95 infected fish.
After birds had visited the pen for three weeks, Lafferty
and Morris added up how many fish were alive. (The covered pen acted as a control for the researchers to see how many fish died of natural causes.) The results were startling: The birds were 30 times more likely to feast on one of the flailing, parasitized fish than on a healthy fish.
The fluke that Lafferty
studied is but one parasite, living in one salt marsh.