PARENT SESSION
Oral Session # 25: Invasive Species II: Aquatic Systems.
Presiding: G Rilov
Tuesday, August 5. 8:00 AM to 11:30 AM, SITCC Meeting Room 205.

Community effects of invasive crayfish: Evidence from long-term, whole-lake surveys.

Rosenthal, Sadie^*,1, Lodge, David¹, Kershner, Mark², ¹ University of Notre Dame, Notre Dame, IN² Kent State University, Kent, OH

ABSTRACT- Previous laboratory studies and in-lake caging experiments suggest that invasive rusty crayfish (Orconectes rusticus) reduce macrophyte abundance and change species composition in north temperate lakes. Using long-term, whole-lake studies, we test whether these effects are manifest in nature. In 1987 and 2002, we censussed crayfish and macrophytes in eleven lakes in northern Wisconsin. Between 1987 and 2002, three of six lakes shifted from low to high crayfish abundances and two of five lakes shifted from high to low. The remaining six lakes changed little. Both lakewide macrophyte abundance and species richness per transect (of 43 total species found) decreased as male rusties per trap increased (linear regression: r²=0.418, p=0.032 and r²=0.700, p=0.001). These relationships were driven by habitat patches with sand substrate where, as opposed to soft organic sediments, we expected crayfish to move easily and have a greater impact on plants. To examine whether macrophyte species composition differed between high and low rusty lakes and whether composition changed over time, we compared Detrended Correspondence Analysis results from 1987 with those from 2002. Analyses were based on the frequency of occurrence for the 18 most common macrophyte species over all eleven lakes. We found that no axis delineated high and low crayfish lakes in 2002, and only one newly invaded lake moved substantially in ordination space between 1987 and 2002. We are currently examining two possible non-exclusive explanations for this: (1) because crayfish are relatively nonselective consumers, they do not alter the occurrence of common species, and/or (2) crayfish are selective towards particular species, but in lakes where these species do not occur, composition remains unchanged. In summary, these surveys suggest that rusty crayfish negatively affect macrophyte abundance and diversity but that changes in species composition may be lake specific.

Key words: Orconectes rusticus, invasive species, macrophytes, long-term effects