Ms. G. (Gissell) Lacerot Silveira, MSc: Effects of climate on size structure and functioning of aquatic food webs


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6 Apr 2010 13:30

Unit: Wageningen University

Location: Aula, building 362, Gen. Foulkesweg 1, Wageningen

Organisation: Wageningen University

Promotor: prof.dr. M. Scheffer (Aquatic Ecology and Water Quality Management)

Co Promotor: Dr.ir. M.F.L.L.W. Lurling

Freshwater of good quality is a limited resource. Excessive algal development depends on nutrient load and also the potential of algal control through the aquatic food chain (“trophic cascade”). Algae biomass can be kept low by zooplankton. However, when fish predation is strong, large-bodied zooplankters-like water fleas-disappear and only small species remain, which are less effective at controlling algae. In temperate lakes this insight led to the use biomanipulation to improve water quality. It implies that fish density is reduced to increase the abundance of water fleas. However, these mechanisms work quite differently in (sub)tropical lakes, and might be altered in temperate lakes due to climate change. To answer this question we studied 83 lakes along a latitudinal gradient on the east coast of South America. My research shows that the average body size of fish communities decreases with latitude. Also, while in cold lakes large fish are often piscivores, in warm lakes many large fish eat the same as small fish do. Thus, control of small fish by large fish might be weaker in warmer climates. Just as fish, the body size of zooplankton decreases from cold to warm climates being small fish predation the main cause of this phenomenon. These results provide an indication of the way in which climatic change may affect water quality of shallow lakes.

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