In new research funded by the Environmental Protection Agency, USGS researchers will develop monitoring tools that use parasites to evaluate the health of salt marshes. Parasites may be affected by the biodiversity of the community of hosts that they inhabit. Depending on the impact and particular parasite studied, environmental degradation may either increase or decrease parasitism. In some cases, a high diversity and abundance of parasites may indicate a healthy ecosystem by reflecting high abundances of diverse hosts connected by multiple trophic interactions.

Trematodes, or flukes, that occur in salt marshes are parasites with complex life cycles involving fishes, invertebrates, birds and mammals. If one of the hosts in a trematode’s life cycle is missing, that trematode will not be able to persist. A measure of the trematode community, gathered from dissecting snails that act as the first host, provides a single, integrated snapshot of the hosts that have been in an estuary over the average life-span of the snails that occur there. Such a single measure of ecosystem integrity would otherwise be impossible to obtain, due to the complexities of gathering comprehensive data on fishes, invertebrates and birds.

This technique has already proven useful in assessing the success of habitat restoration at Carpinteria Salt Marsh in California. Trematode parasites increase dramatically after degraded areas are restored. Researchers will now test this technique at several west-coast estuaries, including pristine sites in Baja California, Mexico, where it is predicted that trematodes will be abundant and diverse relative to the heavily degraded estuaries in southern California.

• How do we assess the health of complex ecosystems?
• Do healthy estuaries support more trematode parasites than unhealthy ones?
• Are parasitic ciliates indicators of stressed fishes?

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Selected References

Lafferty, K. D., D. T. Sammond and A. M. Kuris. 1994. Analysis of larval trematode community structure: separating the roles of competition and spatial heterogeneity. Ecology 75: 2275-2285.

Kuris, A. M. and K. D. Lafferty. 1994. Community structure: larval trematodes in snail hosts. Annual Review of Ecology and Systematics 25:189-217.

Lafferty, K. D. 1997. The ecology of parasites in a salt marsh ecosystem. pp 316-332 In, Parasites and Pathogens: Effects on Host Hormones and Behavior. N. E. Beckage and M. Zuk, eds.

Lafferty, K. D. 1997. Environmental parasitology: what can parasites tell us about human impacts on the environment? Parasitology Today 13:251-255.

Lafferty, K. D. and A. M. Kuris. 1999. How environmental stress affects the impacts of parasites. Limnology and Oceanography 44:564-590.

Lafferty, K. D. and D. Kushner. 2000. Population regulation of the purple sea urchin, Strongylocentrotus purpuratus, at the California Channel Islands. pp 379-381 in, DR Brown, KL Mitchell and HW Chang eds., Proceedings of the Fifth California Islands Symposium. Minerals Management Service Publication # 99-0038.