A Century Later: How Non-Native Crayfish Impact the Benthic Ecology of a Pristine Large Lake

SCOTT F. GIRDNER; SUDEEP CHANDRA; FACUNDO SCORDO

Grand Rapids

Congreso; Joint Aquatic Sciences Meeting 2022 in Grand Rapids, Colorado; 2022

American Fisheries Society (AFS) - Association for the Sciences of Limnology and Oceanography (ASLO) - Coastal and Estuarine Research Federation (CERF) - Freshwater Mollusk Conservation Society (FMCS) - International Association for Great Lake Research

Introduced over a century ago to the deepest lake in the United States, Crater Lake (Oregon), non-native signal crayfish (Pacifastacus leniusculus) now threaten the local extinction of an endemic salamander, the Mazama newt (Taricha granulosa mazamae) and impact the benthic ecology of the ecosystem. In the last decade, crayfish have expanded in distribution to occupy nearly 90% of the nearshore. Although newts remain in uninvaded areas, they are almost entirely absent where crayfish reside. Mesocosm experiments revealed that crayfish prey directly on newts, displace newts from cover, and likely increase newt metabolism. Likewise, isotopic signatures of newt and crayfish tissue confirm overlap in the diets of the two species, whereas lakewide benthic surveys show crayfish reduced the abundance of benthic macroinvertebrate food resources by 95%. The reduction in macroinvertebrate grazers has led to an apparent trophic cascade resulting in increased attached algal biomass and benthic metabolism of the nearshore environment, and influenced first documented filamentous algae bloom in this highly pristine lake. Evidence suggests that the proliferation of crayfish within the last decade has led to dramatic ecological changes to the benthic environment with further expansion likely leading to the extinction of the unique population of newts. Developing management and conservation plans as well as finding resources to implement conservation strategies for the newt is critical for this globally iconic resource.