New findings affirm risk of zebra mussel spread through downstream drift
Recent findings from MAISRC’s Dr. Mike McCartney are shedding light on whether and how zebra mussels infest downstream lakes via natural waterway connections – a risk that we may overlook if we focus entirely on human-aided transport. Data is showing that while simply being connected to an infested lake does not guarantee infestation in a downstream lake, it significantly increases the likelihood.
Over the past two summers, McCartney and his team collected samples from lakes and streams throughout the state – all of which had a connected, infested lake upstream – and counted veligers within the waterbodies and at increasing distances downstream. They also installed cinder block samplers to count the zebra mussel juveniles that settled on the stream bottom. Their analysis showed that:
- Zebra mussel veligers are traveling downstream– sometimes up to a billion per day –and especially in June. However, these numbers decline sharply with distance and can drop to zero prior to reaching downstream water body in some cases.
- Most veligers are not settling on the stream bottom, but if they do, they do so only very close to the upstream lake (within a kilometer). The veligers that aren’t settling on the stream bottom may be delivered out of the stream into lakes or rivers where they might settle, mature, and eventually reproduce.
This new information reaffirms the Minnesota DNR’s policy of listing lakes downstream of known infested lakes as also infested, regardless of whether a live zebra mussel has been found. Essentially, the likelihood of a downstream lake becoming infested is high enough that it warrants the regulations that are enforced on confirmed infested lake.
“It’s not a given, but it’s better to be cautious,” said McCartney. “What is interesting here is how sharp the declines were, and where and in which months the veliger populations dropped to zero. Why does that happen and are there any clues here for prevention and control?”
Going forward, more unknowns – such as the viability of veligers, the distances over which they are dropping off as they travel downstream, and the reasons why – are being and will be addressed. Ultimately, these data will be coupled with boater movement data to allow researchers to make more reliable predictions about the likelihood of future lake invasions, which can be used to better target prevention efforts.
These findings also reinforce the critical aspect of preventing spread whenever possible: once a lake is infested, it may infest many more. Learn more about zebra mussel research and what you can do to prevent spread here.