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Ecosystem energetic implications of parasite and free-living biomass in three estuaries


Parasites can have strong impacts but are thought to contribute little biomass to ecosystems1,2,3. We quantified the biomass of free-living and parasitic species in three estuaries on the Pacific coast of California and Baja California. Here we show that parasites have substantial biomass in these ecosystems. We found that parasite biomass exceeded that of top predators. The biomass of trematodes was particularly high, being comparable to that of the abundant birds, fishes, burrowing shrimps and polychaetes. Trophically transmitted parasites and parasitic castrators subsumed more biomass than did other parasitic functional groups. The extended phenotype biomass controlled by parasitic castrators sometimes exceeded that of their uninfected hosts. The annual production of free-swimming trematode transmission stages was greater than the combined biomass of all quantified parasites and was also greater than bird biomass. This biomass and productivity of parasites implies a profound role for infectious processes in these estuaries.

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Figure 1: Biomass of animals and proportional contribution of parasites in three estuaries.
Figure 2: Ecosystem-level biomass density of animal parasites in three estuaries.
Figure 3: Ecosystem-level biomass density of parasitically castrated (extended phenotypes) and uninfected phenotypes of hosts supporting parasitic castrators in three estuaries.
Figure 4: Standing crop biomass and cercarial productivity of trematodes in Cerithidea californica snails.


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We thank many assistants, in particular I. Jimenez, A. Kaplan, M. Saunders, J. Smith, A. Wood and the research team of L. Ladah. L. Ladah and the Huttinger family provided facilities for fieldwork. Satellite imagery of CSM was provided by K. Clarke. The University of California Natural Reserve System provided access to CSM. The National Science Foundation/National Institutes of Health Ecology of Infectious Diseases Program provided funding.

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Correspondence to Armand M. Kuris.

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Kuris, A., Hechinger, R., Shaw, J. et al. Ecosystem energetic implications of parasite and free-living biomass in three estuaries. Nature 454, 515–518 (2008).

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