INVASIVE CRAYFISH ORCONECTES RUSTICUS (DECAPODA, CAMBARIDAE) IS A MORE EFFECTIVE PREDATOR OF SUBSTRATE NESTING FISH EGGS THAN NATIVE CRAYFISH (O. VIRILIS)

Non-indigenous crayfish pose substantial threats to native species, community structure, and ecosystem function in invaded lakes across the globe. The well-documented range expansion of the rusty crayfish Orconectes rusticus is an ideal system to study potential relationships between the attributes that contribute to invasive success, and the ways in which non-indigenous species alter invaded systems. In Michigan and northern Wisconsin (U.S.A.) lakes where O. rusticus is replacing its native congener O. virilis, it is thought that O. rusticus invasion may account for decreased fish abundance. However, not all of the potential mechanisms that could drive this process have been explored. We examined the hypothesis that O. rusticus are better benthic egg predators than O. virilis, and tested the prediction that O. rusticus would consume substrate bound fish eggs at a higher rate than its native congener. Support for this hypothesis would suggest that O. rusticus may be able to access a high-energy food source better than O. virilis, and exert predation pressures that could limit the abundance of fish species which might otherwise limit crayfish populations through top-down control. In laboratory experiments, we determined that O. rusticus exhibit a positive correlation between feeding rate and carapace length not displayed by O. virilis, and that larger O. rusticus feed at a higher rate than their native congener. We also found that O. rusticus in laboratory feeding trials engaged in longer feeding events than crayfish foraging in situ in a substrate-spawning fish nest, a factor which could give O. rusticus an advantage in resource competition with its native congener O. virilis. Collectively, these findings support the hypothesis that O. rusticus is a better predator of substrate bound fish eggs than O. virilis, and suggest that direct predation by crayfish may influence fish reproduction in lakes where O. rusticus replaces O. virilis.