22 October 2010 Last updated at 05:53 ET
Warming 'destabilises aquatic ecosystems'
By Mark Kinver Science and environment reporter, BBC News
Future warming could have "profound implications" for the stability of freshwater ecosystems, a study warns.
Researchers said warmer water affected the distribution and size of plankton - tiny organisms that form the basis of food chains in aquatic systems.
The team warmed plankton-containing vessels by 4C (7F) - the temperature by which some of the world's rivers and lakes could warm over the next century.
The findings appear in the journal Global Change Biology.
"Our study provides almost the first direct experimental evidence that - in the short-term - if a [freshwater] ecosystem warms up, it has profound implications for the size structure of plankton communities," said lead author Gabriel Yvon-Durocher from Queen Mary, University of London.
"Essentially, what we observed within the phytoplankton (microscopic plants) community was that it switched from a system that was dominated by larger autotrophs (plants that photosynthesise) to a system that was dominated by smaller autotrophs with a lower standing biomass."
Dr Yvon-Durocher added that a greater abundance, but lower overall biomass, of smaller phytoplankton had "very important implications for the stability of plankton food webs".
"This meant that the distribution of biomass between plants and animals changed from a... situation where you had a large amount of plants and a smaller amount of animal consumers to an 'inverted pyramid' where you have a smaller quantity of plant biomass and a larger amount of animal biomass," he told BBC News.
"Systems that tend to have larger consumer biomass relative to the resource biomass tend to be less stable over time."
Dr Yvon-Durocher explained that phytoplankton played a key role in the food webs of oceans, rivers and lakes.
"An inordinate amount of the primary productivity and carbon draw-down in ocean and