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Miami research provides insight into fisheries productivity

12/05/2008

Miami researchers find food chain efficiency strongly related to ratio of sunlight vs. nutrients available to algae.
A study by Miami University researchers of the efficiency of energy transfer through food chains provides insights into sustaining ecosystem services - such as fisheries - on which humans rely.

"Light, nutrients, and food-chain length constrain planktonic energy transfer efficiency across multiple trophic levels" is published in the Nov. 25, 2008, Proceedings of the National Academy of Sciences (PNAS). Authors are Elizabeth Dickman and Jennifer Newell (both MS '07), Maria Gonzalez, associate professor of zoology and Michael Vanni, professor of zoology.

"Our paper shows that the efficiency with which energy is propagated through food chains is strongly related to the ratio of sunlight versus nutrients available to algae," says Gonzalez. "Thus, the productivity of fisheries harvested by humans, one of the most globally important ecosystem services, may be very sensitive to this ratio."

Food chain efficiency (FCE) is the proportion of energy fixed by primary producers (plants) that is transferred to the top of the food chain (large predators). In the first study to test experimentally whether light and nutrients interactively regulate food chain efficiency across three trophic levels (plants, herbivores and carnivores), Miami researchers found that FCE is constrained by algal food quality and food-chain length. Specifically, FCE was higher under conditions of low sunlight and high nutrients.
Many global environmental perturbations affect light, nutrients and food-chain length, and many ecological services are mediated by FCE, say the study authors. For example, algal bloom (eutrophication) increases nutrient supply and decreases light intensity in aquatic systems, while climate change can alter nutrient supply, light and temperature.

"Understanding how light and nutrient supplies mediate FCE may help explain some of the observed variation in the relationship between primary production and fishery yields," say the researchers. "It will be important to apply these findings to various ecosystem types."

The research was conducted at Miami's Ecological Research Center aquatic facilities. It was supported by grants awarded to Gonzalez and Vanni from the Cooperative State Research, Education and Extension Service, U.S. Department of Agriculture and from the National Science Foundation.

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