They tend to knock back common species, and that provides opportunities for biodiversity.” “They're important because they're regulators. “I think the general statement that parasites are embedded in and dominate food webs is true everywhere,” Lafferty says. Just offshore, periodic bacterial disease outbreaks depress populations of kelp-grazing sea urchins and allow kelp forests to rebound. Trematodes prevent infected cockles from burrowing in the mud, leaving shells exposed as hard surfaces where sessile organisms can attach. Parasites also influence the physical habitat. In the marshes that Lafferty studies, for instance, trematodes manipulate the behavior and reproductive success of their multiple hosts: The worms castrate the snails they infect and use them to produce hordes of free-swimming trematode larvae when the larvae burrow into the tissues of killifish, they form cysts in the brain that cause the fish to flash on their sides at the water's surface, where they are much more likely to be eaten by birds, in whose guts the worms complete their life cycle. Marine parasites (including disease-causing pathogens) are not just weighty and numerous, they also play powerful roles in orchestrating the makeup, diversity, and health of natural marine communities. Nowhere is that truer than in the oceans, where both host and parasite diversity exceed that on land. Yet parasitism is the most popular lifestyle among animals.”
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“Ecologists have been slow to truly recognize this because there's not a tradition of looking inside organisms. “Parasites and pathogens are everywhere, and that's a normal state of nature,” says Lafferty, a US Geological Survey marine ecologist at the University of California-Santa Barbara. Yet calculations by Lafferty and Armand Kuris show the biomass of trematode parasites alone-flatworms such as flukes-contained within the visible creatures may exceed that of the birds in a healthy estuary.
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Only Kevin Lafferty and a few like-minded colleagues look at the same scene and envision packets of parasites and pathogens on the move.
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Most visitors to salt marshes along the southern California coast will spot Caspian terns, plovers, and sandpipers feasting on snails, crabs, and killifish at low tide.