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Parasites Permeate Ecosystems

A study shows that parasites can make up three percent of an ecosystem's biomass--and even outweigh the so-called top predators. Karen Hopkin reports.

[The following is an exact transcript of this podcast.]

When you think about an ecosystem, you usually think of the big animals that live there. The Serengeti’s ruled by lions. And estuaries are populated by fishes, birds, snails and maybe the occasional otter. But there’s more to an ecosystem than meets the eye. Because a team of scientists from the US and Mexico has found that parasites constitute a sizeable chunk of the biomass of an ecosystem.

The scientists catalogued and weighed all of the plants, animals and parasitic species living in three river estuaries. They found that in terms of sheer bulk, parasites represent about three percent of the biomass of these ecosystems. Pound for pound, one parasite—the trematode fluke that infects a certain snail—outweighs all of the estuaries’ birds, which are the ecosystem’s top predators. The results appear in the July 24 issue of Nature. That means that creatures you can’t see might be even more important to the health of an ecosystem, and to its balance of power, than the ones you can see. For example, in these estuaries, snails that are infected with trematodes outnumber those that are fluke-free. Now that’s what you call a controlling interest.

—Karen Hopkin

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