Characterizing long-term Spiny waterflea impacts using paleolimnology data
Spiny waterflea (Bythotrephes longimanus) represent a serious potential threat to the structure and function of food webs in Minnesota lakes, but little is known about how they change a lake’s ecology and whether time delays occur before potential changes manifest in an invaded ecosystem. In particular, how their establishment and proliferation translate into impacts on the food webs of native zooplankton, phytoplankton, and game fish remains poorly known.
Previous studies have shown that spiny waterflea first appeared in lake sediments in Island Lake Reservoir (Duluth, MN) up to eight years before its first detection in the water, suggesting that ecosystems may be invaded for several years prior to discovery. This evidence shows that in order to truly understand long-term food web impacts, scientists must first have a stronger understanding of exactly when spiny waterfleas arrived.
Therefore, this project will determine the types, magnitude, and timing of changes that occur to lakes after spiny waterfleas invade by describing and comparing long-term historical trends in key components of the food webs of two invaded lakes (Kabetogama Lake and Mille Lacs Lake) and two non-invaded, control lakes (Leech Lake and Winnibigoshish Lake).
Researchers are using dated lake-sediment cores to reconstruct long-term environmental histories. Spiny waterfleas are very well-preserved in lake sediment and can be used to study food web dynamics, when they were first present, their growth trajectories, and their early impacts on prey. The results will document the changes occurring from 1970 to present. This long period allows for the evaluation of initial detection of spiny waterflea as well as other factors such as climate change or zebra mussels that may be driving change.
Research will be conducted in partnership with staff from the Minnesota Department of Natural Resources and Voyageurs National Park to use their long-term gill-net and seining survey data to assess the type, chronology, and magnitude of fishery changes following a spiny waterflea invasion.
This research will help prioritize spiny waterflea as an issue and give managers a more clear idea about its sense of urgency, the magnitude of problem, and the lag time associated with an invasion. It will also help define threats to sport fishing, water quality, and the overall food web.
As of July 2018, all needed sediment cores have been collected from Mille Lacs and Lake Kabetogama. The cores are being processed for water and organic content, isotopic aging, zooplankton subfossils, and algae pigments. The cores are also undergoing isotopic aging. Results are suggesting that spiny waterflea were present in Mille Lacs and Kabetogama for decades before they were detected in the water column. As of January 2019, researchers were analyzing sediment cores for zooplankton subfossils and algae pigments back to 1970. Early results are indicating that spiny waterflea were present in Lake Mille Lacs and Lake Kabetogama for decades before it was first detected in the water column (first water column detection was in 2009 in Mille Lacs, and in 2007 in Kabetogama). All three cores searched from Mille Lacs and all three cores searched from Kabetogama provide evidence that spiny water flea was present in both lakes during the 1970s. Additional results indicate that several prey species of spiny water flea increased in density at about the time spiny water flea began to increase in density (between 1990-2010). These assessments are preliminary and will need to be confirmed and refined with additional analyses.