The role forest matter plays in aquatic food chains is a relatively recent discovery.

Deforestation is reducing the amount of leaf litter falling into rivers and lakes, resulting in less food being available to fish, a study suggests.

Researchers found the amount of food available affected the size of young fish and influenced the number that went on to reach adulthood.

The team said the results illustrated a link between watershed protection and healthy freshwater fish populations.

The findings have been published in Nature Communications.

"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," explained lead author Andrew Tanentzap from the University of Cambridge's Department of Plant Sciences.

"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 added.

Dr Tanentzap observed: "Where you have more dissolved forest matter you have more bacteria, more bacteria equals more zooplankton.

"Areas with the most zooplankton had the largest, fattest fish," he added, referring to the study's results.

The team of scientists from Canada and the UK collected data from eight locations with varying levels of tree cover around Daisy Lake, Canada, which forms part of the boreal ecosystem.

Climate change 'may shrink fish'

 

 
Fish body size is related to the water's temperature and oxygen levels, says the team
 

Fish species are expected to shrink

in size by up to 24% because of global warming, say scientists.

Researchers modelled the impact of rising temperatures on more than 600

species between 2001 and 2050.

Warmer waters could decrease ocean oxygen levels and significantly reduce

fish body weight.

The scientists argue that failure to control greenhouse gas emissions will

have a greater impact on marine ecosystems than previously thought.

Previous research has suggested that changing ocean temperatures would impact

both the distribution and the reproductive abilities of many species of fish.

This new work suggests that fish size would also be heavily impacted.

The researchers built a model to see how fish would react to lower levels of

oxygen in the water. They used data from one of the higher emissions

scenarios developed by the Intergovernmental Panel on Climate Change (IPCC).

Warming the fish

Although this data projects relatively small changes in temperatures at the

bottom of the oceans, the resulting impacts on fish body size are "unexpectedly

large" according to the paper.