Long-term relationships between rusty crayfish and macrophytes in lakes

The rusty crayfish (Orconectes rusticus), a species native to Ohio and Indiana, has been invading lakes throughout northern Wisconsin for the past several decades (Hobbs et al. 1989).  This exotic species has the ability to outcompete native crayfish species (Hill and Lodge 1999) and often replaces native crayfish species in the lakes it invades (Olsen et al. 1991).  In addition, the rusty crayfish often occurs at higher population densities than the native species and has been associated with reductions in macrophyte biomass.  Because macrophytes provide important foraging and reproductive habitat to fish and other aquatic organisms, the relationship between rusty crayfish abundance and macrophyte biomass has been of interest to scientists, lake managers, anglers, and the general public.  Long-term observations of rusty crayfish abundance and macrophyte biomass in Trout Lake, one of the North Temperate Lakes LTER program's primary study lakes, have shown an inverse relationship over the past 18 years (Figure1).  Interestingly, in the first seven years of record (1983-1989), when rusty crayfish abundance was increasing rapidly at this site in the lake, there was no evident decline in macrophyte biomass.  The inverse relationship between rusty crayfish and macrophyte biomass, which has also been established experimentally (Lodge and Lorman 1987), was only apparent after 12-15 years of record, indicating the importance of long-term data in these lakes.

Literature Cited

Hill, A.M. and D.M. Lodge.  1999.  Replacement of resident crayfishes by an exotic crayfish: The roles of competition and predation.  Ecological Applications 9:678-690.

Hobbs, H.H.I., J.P. Jass and J.V. Huner.  1989.  A review of global crayfish introductions with particular emphasis on two North American species (Decapoda, Cambaridae).  Crustaceana 56:299-316
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Lodge, D.M. and J.G. Lorman.  1987.  Reductions in submersed macrophyte biomass and species richness by the crayfish Oronectes rusticus.  Canadian Journal of Fisheries and Aquatic Sciences 44:591-597.