Phase II: Historical analyses of spiny waterflea invasion patterns
Preliminary results of Phase I (below) show that spiny waterflea have been present in Lake Kabetogama and Lake Mille Lacs continuously since 1970. It was previously thought that spiny waterflea arrived in North America during the late 1970s or early 1980s. The second phase of this project will advance our ability to test key cause-and-effect hypotheses about relationships between spiny waterflea invasion and the response of important ecological, economic, and recreational services provided by Minnesota lakes including zooplankton abundance, fish abundance, and water clarity. This will be accomplished through:
- Measurements of the rates of lake sediment mixing in Lake Kabetogama and Lake Mille Lacs
- Recovery of evidence of spiny waterflea in lake sediment cores that were collected before the species was first detected in the open water plankton of three infested Minnesota lakes (Kabetogama, Rainy, and Trout) through the study of previously collected and archived sediment core material
- Estimate rates of production of spiny water flea in Lake Kabetogama and Lake Mille Lacs, and use the results to calibrate accumulation rates of spiny water flea in sediment cores (this goal will be accomplished with in-kind support from the Minnesota Department of Natural Resources)
Phase I: 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.
This project made large advances in understanding the colonization and impact of spiny water flea in Lake Mille Lacs, Lake Kabetogama, Lake Winnibigoshish, and Leech Lake through the collection and analysis of organism remains in lake bottom sediments over about a 120 year period from present (2017 or 2018) back to the year 1900. The results provide replicated evidence that spiny water flea was resident continuously in Lake Mille Lacs and Lake Kabetogama since the 1930s, or about 80 years before it was first detected in the open waters of either lake. Evidence demonstrates that spiny water flea had a prolonged history of low abundance in both lakes before about the year 2000 at which time it began to increase rapidly. Zooplankton that are prey and competitors of spiny water flea often declined in abundance after spiny water flea increased in abundance. There was no evidence of spiny water flea in the sediments of Lake Winnibigoshish. There was evidence of a small population of spiny water flea in the sediments of Leech Lake that dated to the year 2001, possibly representing a failed invasion. To date, Leech Lake has never been known to contain this organism. The data allow us to test hypotheses about the timing and impact of spiny water flea on the food webs of Minnesota lakes. The results re-cast our understanding of the timeline of spiny water flea invasion in Minnesota and underscore the value of lake sediments to study invasive species. The results suggest that traditional methods of spiny water flea detection with nets, as carried out by academic units and management agencies in Minnesota, may be inadequate to detect spiny water flea when it is low or transient in abundance.