The decline of just one fish species can disrupt an entire ecosystem, study finds

Common scientific wisdom posits that a diverse ecosystem can still thrive if a species within it declines. But a new study found that when just one important species in a river declined, the ecosystem was seriously changed and other species did not compensate.

The flannelmouth characin is a fish that is harvested in South America; it feeds on the organic matter on river bottoms that influences carbon flow and nutrient cycling. When Cornell ecologist Alexander Flecker and colleagues, including lead researcher Brad W. Taylor '93, removed the species from a small stretch of a river in Venezuela, they found that the flow of organic carbon in the river dramatically changed, the researchers reported in the Aug. 11 issue of the journal Science.

Because the organic matter that shades nitrogen-fixing algae was no longer eaten by the removed species, biomass on the streambed increased 450 percent. "That resulted in much more bacterial respiration, which, in turn, converted more carbon to carbon dioxide and decreased the amount of carbon swept downstream for other organisms," said Flecker, associate professor of ecology and evolutionary biology.

The loss or decline of just this one species could reverberate throughout the stream's network and have long-lasting negative feedbacks on the food web, affecting fish populations, algae, bacteria, insects and other fish species, as well as ecosystem function and the flow of protein to humans and other animals, eroding an important ecosystem service, the authors conclude.

Other researchers include Taylor, now at Dartmouth College, and Robert O. Hall Jr. '89, now at the University of Wyoming.

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