From: Allison Winter, ENN
Published June 11, 2014 12:39 PM

How forest debris affects freshwater food chains

While one may think that forest and lake ecosystems are two separate networks, new research shows how forest debris is an important contributor to freshwater food chains.

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How? Debris in the form of organic carbon from trees washes into freshwater lakes, which consequently supplements the diets of microscopic zooplankton and the fish that feed on them.

Researchers at the University of Cambridge conducted a study at Daisy Lake in Ontario, Canadian by observing Yellow Perch fish from different parts of the water body with varying degrees of surrounding forest cover.

Carbon from forest debris has a different elemental mass than carbon produced by algae in the aquatic food chain. By analyzing the young Perch that had been born that year, scientists were able to determine that at least 34% of the fish biomass comes from vegetation, increasing to 66% in areas surrounded by rich forest.

Essentially, the more forest around the edge of the lake, the fatter the fish in that part of the lake were. Similarly, the sparser the forest leaves, the smaller the fish.

"We found fish that had almost 70% of their biomass made from carbon that came from trees and leaves instead of aquatic food chain sources," said Dr Andrew Tanentzap from Cambridge's Department of Plant Sciences, and lead author of the new study, published today in the journal Nature Communications.

"While plankton raised on algal carbon is more nutritious, organic carbon from trees washed into lakes is a hugely important food source for freshwater fish, bolstering their diet to ensure good size and strength," he said.
The new research builds on previous work that showed that algae is not the only source of food for zooplankton, but that they also feed on bacteria from forest matter drained into lakes.

"More than 60% of the world's fresh water is in the boreal areas such as Canada, Scandinavia and large parts of Siberia. These areas are suffering from human disturbance such as logging, mining, and forest fires resulting from climate change — all occurrences predicted to intensify in coming years," said Tanentzap.

The researchers warn that, as forests are eroded through human activities such as logging, the impacts will be felt in aquatic as well as terrestrial food chains.

Read more at the University of Cambridge.

Lake image via Shutterstock.

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