During the summer of 2007, researchers from the University of Quebec in Montreal conducted an environmental study in Lake Pemichangan on the interaction between two invasive species: rusty crayfish and water milfoil.
Maria José Maezo is a Master’s student in the Department of Biological Sciences at the Université du Québec à Montréal (UQÀM) where she works with Professor Beatrix Beisner as well as with Mr. Henri Fournier of the Ministère des Ressources Naturelles et de la Faune (MRNF) in Gatineau. They are interested in exploring the effects of an invasive species (the Rusty Crayfish: Orconectes rusticus is the scientific name) that is present in Lake Pemichangan.
This species of crayfish originally comes from the Ohio river basin but has been spreading in more recent years largely because it is a very popular live bait for bass fishermen. They suspect this is how it was introduced to Pemichangan in the first place. This species has already been introduced to 20 states, in Ontario and here, with large effects on both native crayfish and aquatic vegetation. Some studies have demonstrated that this crayfish can become very abundant where it is introduced and that it can dramatically reduce aquatic plants. Thus, the interest in exploring more about it’s biology in Lake Pemichangan.
As most of the cottagers on Lake Pemichangan already know, water milfoil (Myriophyllum spicatum) is another exotic species currently invading the lake. The ultimate goal of this project is to determine if the introduced rusty crayfish could actually control this plant. In other words, could one invasive species help combat another invasive? On the other hand, although they eat plants, there is actually a strong possibility that the crayfish could instead contribute to further dispersion of the plant, because it is a messy eater, cutting fragments without consuming them completely. Water milfoil is an especially successful invasive species because it takes advantage of being cut into fragments which can re-root themselves fairly easily to start a whole new plant. In the end, without further study, it is hard to say one way or the other whether rusty crayfish will help or hinder the spread of the exotic water milfoil. Answering this question, at least in part, is the focus of this M.Sc. thesis.
To study the interaction of these two species they conducted a cage experiment. They had a series of cages installed in Lake Pemichangan throughout most of the summer, each containing a different number of crayfish and a fairly even number of milfoil plants (at least when the experiment started). Every week they collected the fragments produced by the crayfish, and at the end of the experiment, they collected the remaining plants to determine their impact on the total plant biomass. In addition to the cage experiment, Maria surveyed the lake throughout the summer to see if there was a relationship between the distributions of the two species. Although they haven’t yet had time to work through the data, one thing they have discovered is that the majority of the crayfish population in Lake Pemichangan is actually composed of hybrids (i.e. the native species of crayfish has cross-bred with the introduced rusty crayfish). This suggests that the introduced crayfish has been here for quite a while – probably at least a few years to a decade, maybe even more. Other preliminary results suggest that it takes a very high density of crayfish to have a negative impact on the milfoil and that crayfish in the lake are probably not dense enough to eliminate it. However, the final verdict will have to wait until all the data is in!