Zebra mussel investigations: pathways and mechanisms of spread, new molecular approaches for early detection, and methods for estimating population change in response to pesticide treatment

Project manager: Michael McCartney

Description: Today, zebra mussel invasions of inland lakes in Minnesota are clearly on the increase. Further containment and control require knowledge of invasion pathways and mechanisms in the state, which remain unstudied. They also require early detection of new invasions, methods for which (visual counts by microscopy) are reliable but they are slow and at present, positive results cannot be confirmed by an accepted independent technique. Confirmation is particularly called for in the case of early invasions, in which a positive detection may be a small number of veliger larvae from lakes in which adult mussels have yet to be found, and for which the costs of an infested designation to local economies can be substantial.

Activity 1: Evaluating pathways and mechanisms of spread

Our first objective is to use population genetics of highly variable microsatellite DNA and Single Nucleotide Polymorphism (SNP) markers to evaluate the sources of inland invasions throughout Minnesota, and the pathways through which zebra mussels have spread throughout the state. In addition to history, this work will provide managers a basis for focusing prevention—for example, they may be able to gauge the extent to which mussels are currently being spread from the Mississippi River, or from a large inland lake source (such as Mille Lacs).

Progress: A diverse set of samples – 1,281 mussels from 16 lakes and 3 river systems – have been genotyped and analyzed for genetic structure and invasion modeling. In partnership with the University of Minnesota Genomics Center, Illumina paired-end sequencing of genomic DNA extracted from a single mussel is now complete. Analysis is also complete for the microsatellite markers for the initial set of ten lakes. Preliminary analysis finds reason to question the “super spreader” concept and also suggests that inspection and enforcement has historically been more effective than some realize. These results are now being checked over a larger sample of lakes.

Activity 2:  Studying downstream drift as a mechanism of spread of zebra mussels between lakes

Our second objective is to address the spread mechanism of "downstream drift" in coupled lake/small stream systems throughout the state. Downstream drift is the natural mechanism of spread between water bodies through downstream dispersal of veliger larvae, which settle and found populations of mussels within the stream, as well as populations in the water body into which the stream flows. This project will estimate the flux (i.e. the number of veliger larvae that drift downstream per day) into the downstream water body throughout the reproductive season, how this flux changes with distance from the upstream lake, and the rate of settlement of juvenile mussels at increasing distances downstream. This work will be conducted in streams with varying lengths, stream discharge rates, and population densities of zebra mussels in upstream lakes to examine the influence of these factors on the magnitude of downstream drift.

Progress: Veliger sampling and analysis has been completed and the risk of downstream drift has been affirmed. Read more here.

Activity 3: Developing and testing a new molecular assay for early detection of zebra mussel veligers

Our third objective is to develop a new rapid molecular assay for early detection of zebra mussel veliger larvae, and test the assay performance in control experiments and on field samples from lakes throughout Minnesota. Through this process we will develop a reliable, sensitive, and rapid molecular alternative to the microscopy assay, presently used as a standard method. The molecular assay, we envision, will be used as an alternative to check the validity of positive detections, particularly in high priority lakes. With further development, the molecular assay will be an inexpensive, and – particularly with automation – a very rapid way to screen water bodies for early detection.

Progess: Researchers have successfully developed a new molecular detection assay for the early detection of zebra and quagga mussels DNA and larvae. This new tool will improve critical early detection efforts which increase the likelihood of controlling a new infestation. Read more here.

Project start date: 2013

Estimated project end date: 2016