Crayfish Large Lake Ecosystems: Seasonal Dynamics and Ecological Impacts

Crayfish are widely recognized as an important benthic consumer that regulates the flow of energy, nutrients, and controls biodiversity within aquatic ecosystems. In the Western United States the signal crayfish (Pacifastacus leniusculus) was introduced outside of its range to provide food for humans and increase forage for game fish.  While most of the studies investigating impacts of crayfish introductions have focused on small streams and lakes, here we discuss the introduction history, distribution, and impact of crayfish in two large lake ecosystems, Crater (Oregon) and Tahoe (CA-NV).  Introduced to provide food for the local population in the late 1800’s to early 1900’s, the signal crayfish have doubled in catch since first, quantitative measurements were undertaken in the 1970’s.  The rate of increase is thought to occur due to the introduction of the opossum shrimp (Mysis relicta) and subsequent shift of predation by nonnative lake trout (Salvelinus namaycush) combined with increases in littoral zone productivity due to eutrophication. The crayfish in Tahoe distribute largely in the littoral zone (0-40 m) in the summer with migrations into the deeper waters (>100 m) in the winter and spring. While introduced in Crater Lake in 1914, it is only in the last decade that Park limnologists have noticed the rapid increase of crayfish around the lake. Currently crayfish are only found at two locations in Crater Lake with samples as deep as 250 meters. It is unclear if crayfish are expanding at the fringe in the nearshore however biodiversity and biomass of invertebrates was significantly depressed in both soft and hard substrate when crayfish are present. Snails and amphibians were completely absent in areas with crayfish present. Our preliminary data suggest that crayfish are able to achieve widespread distribution on large, deep oligotrophic lakes with impacts to select taxa within the amphibian and invertebrate community.