UCSB Team to Study Ecosystem Role of Parasites

UC Santa Barbara researchers have been notified that the National Science Foundation will award $2.2 million over five years to the Marine Science Institute to study the role of parasites in natural ecosystems.

"We seek to reveal how anthropogenic or human-induced changes, particularly those related to biodiversity loss and habit transformation, influence communities of parasites with complex life cycles," said Armand Kuris, one of three co-principal investigators and a professor of zoology.

In their proposal, the researchers explain how the ecology of parasites has long had implications for human health and that human alterations to the environment have affected the success of parasites: "Humans have altered the globe in ways that favor diseases. For example, deforestation, damming, fish farming and rice farming have increased malaria transmission by creating mosquito breeding habitats."

The researchers will work in salt marshes because these have proven to be a model system for understanding the ecology of parasites with complex life cycles. In addition to two UCSB natural reserves—Carpinteria Salt Marsh and Coal Oil Point—the researchers will travel to estuaries in Morro Bay, Mugu Lagoon, Japan, and along the Pacific coast of Baja California.

"The types of changes most likely to affect parasite communities are alterations in host communities resulting from climate change and environmental degradation," said Kevin Lafferty, who is a co-principal investigator, an adjunct professor of biology at UCSB, and also works for the U.S. Geological Survey.

Contrary to most expectations about disease, he noted that healthier, less degraded ecosystems tend to have more parasites with complex life cycles because these parasites depend on functioning ecosystems.

Lafferty explained that environmental degradation could include introduced species, habitat fragmentation, pollution, and overharvesting. In turn, because parasites, particularly those transmitted when an organism eats an infected host, have the potential to organize their host communities, changes to parasite communities can profoundly alter natural systems. "We are especially interested in the potential for complex feedback dynamics initiated by anthropogenic change," he said.

The new research ties in with current research by Lafferty and colleagues at UCSB funded by the EPA to develop parasites as indicators of estuary health and function.

Kuris, Lafferty and a third investigator, Andrew P. Dobson, professor of zoology at Princeton, are specialists in parasite ecology. They will use mathematical models, molecular tools, laboratory experiments, field experiments, and large-scale comparative field studies for the investigation.

The researchers will study parasites of the abundant horn snail, Cerithidea californica, which acts as a hub in the life cycle of 17 parasitic trematode (worm) species. Each worm moves through several hosts. A worm castrates the snail it infects and each day produces scores of free-swimming stages that leave infected snails to search out a second intermediate host such as a fish, clam, crab, or another snail.

In the second intermediate host, the trematode can greatly alter host behavior to increase the chance of transmission to a final host. Wading birds, shorebirds, and seabirds prey selectively on second intermediate hosts and become parasitized by adult worms. In the final host, the small worms live in the gastrointestinal tract, mate, and produce eggs that pass into the marsh with the host's feces where they encounter snails and complete the life cycle. Each of the trematode species that use C. californica has a different life cycle.