Analysis of long-term data to understand food web dynamics - Carpenter's cascade and the spring clear water phase

Long term data and their analyses are critical for understanding ecosystem dynamics and importance of invasive species.  Many years ago, I was a postdoc with Steve Carpenter on the Lake Mendota biomanipulation project.  The analysis of these data showed the importance of the specific Daphnia species on the seasonality of the spring clear-water phase which in turn depended on fish abundance.  Since then, I have studied similar phenomena using another long-term data set from Oneida Lake, New York, studies heavily influenced by Carpenter.  Although clear-water phase in the past was also the result of fish-Daphnia-phytoplankton dynamics, the clear water phase was primarily affected  by zebra and quagga mussels after their invasion in early 1990s.  Further, the replacement of zebra with quagga mussels by 2009 changed the seasonality and extent of the clear water phase as quagga mussels are active at lower temperature and build up higher biomass than zebra mussels.  For this polymictic lake, benthic grazers dominate and species-specific difference in the two dominant benthic grazers matters. Generalizing among lakes need to include benthic grazers and their ability to access the water column which is affected by temperature stratification. Fro example, although zebra mussels are now in one of Steve’s favorite lakes – Lake Mendota – they are likely to be less important compared to Oneida Lake due to summer stratification and low oxygen conditions. In a stratified lake in New York with low summer oxygen, Daphnia remained the main driver of clear water phase even after the invasion of zebra and quagga mussels.

Primary Presenter: Lars Rudstam, Cornell University (lgr1@cornell.edu)

Authors:

Lars Rudstam, Cornell University  (lgr1@cornell.edu)