Zooplankton in freshwaters : potential responses to global warming, nutrient enrichment, and exotic jellyfish.

Feeding rate;Temperature;Jellyfish;Nutrient effects;Daphnia

Allison S. Smith

University:University of Louisville

Department:Biology

关键词: Feeding rate;    Temperature;    Jellyfish;    Nutrient effects;    Daphnia;   

Others  :  https://ir.library.louisville.edu/cgi/viewcontent.cgi?article=2353&context=etd

美国|英语

来源: The Universite of Louisville's Institutional Repository

【 摘 要 】

Aquatic ecosystems face major transformations as humans increasingly alter their environment by introducing exotic species and changing the temperature regime and nutrient availability of freshwater systems. The impacts of such alterations of conditions, resources and species composition on zooplankton are important to consider because zooplankton link primary producers to higher trophic levels. Among recent exotic invaders of freshwater systems in Europe and the Western Hemisphere is Craspedacusta sowerbii. This freshwater cnidarian can impact zooplankton abundance and community composition, thus altering ecosystem energy transfer to higher trophic levels. In experiments described in chapters 2 and 3 of this dissertation, C. sowerbii was found to have a significant and differential effect on zooplankton taxa such as Bosmina sp., Daphnia sp., and copepods. While medusa greatly reduced abundances of these genera, other potential prey items, such as Keratella sp., did not show a response to medusa presence, indicating that C. sowerbii medusa differentially alter zooplankton communities. However, while C. sowerbii did not affect all potential prey items, some species such as the large D. magna were killed at high rates but not consumed. This indicates that the effects of C. sowerbii medusa presence are not only the result of prey consumption, but also extend to their killing effect on species they cannot ingest. The rate of global warming is predicted to accelerate in the coming decades and temperate freshwater ecosystems will face alterations in response to these changing thermal conditions. Simultaneously we can expect that nitrogen input to aquatic systems will increase through the deposition of fossil fuel combustion products, fertilizer runoff and sewage inputs. Such increased inputs are having and will have greatly affected primary production in freshwater ecosystems. As nitrogen levels increase so does the probability of both primary and secondary producers becoming phosphorus limited. These alterations can have dramatic effects on zooplankton such as Daphnia, a common and important genus of Cladocera in many lakes and rivers. Together warming temperature and increased nitrogen availability are expected to affect the growth and reproduction of aquatic organisms such as Daphnia, which are often the link between primary producers and higher trophic levels. The experiments contained in Chapter 4 reveal that juvenile growth rate and reproductive output of D. magna and D. pulex, two ubiquitous species of Daphnia, can indeed be directly affected by temperature and nitrogen and phosphorus availability. Temperature was found to have the predicted positive relationship with growth rate and