Read this article on the Park Science website.Abstract:
The signal crayfish (Pacifastacus leniusculus) was introduced to Crater Lake in 1915 and is now displacing a native salamander. Before the introduction of this crayfish species, no crayfish existed in the lake. A proposed subspecies of the rough-skinned newt (Taricha granulosa), the Mazama newt (T. granulosa mazamae) is reportedly endemic to Crater Lake, Oregon. The Mazama newt is morphologically, genetically, and physiologically distinct from populations of newts outside of the lake. Observations by park biologists through the 1900s suggested a decline in Mazama newt distribution and an increase in signal crayfish abundance, which led us to investigate current distribution, relative abundance, and interactions between crayfish and newts. Results indicate that crayfish have expanded in distribution to occupy nearly 80% of the lakeshore. Newts remain in areas that crayfish have yet to invade but are almost entirely absent in areas occupied by crayfish. Isotopic signatures of carbon and nitrogen in newt and crayfish tissue indicate that the two species eat similar food items and occupy a similar position (primarily predacious) in the food web. Abundance of other aquatic invertebrates was dramatically reduced in locations with crayfish compared with areas of the lake without crayfish. Mesocosm experiments conducted with newts and crayfish revealed that crayfish prey on newts, displace newts from cover, and generally alter newt behavior when the two species co-occur. This evidence, taken together, suggests that further crayfish expansion likely will cause additional declines in newt abundance and distribution, and could lead to extinction of the unique Mazama newt. Conserving this irreplaceable component of Crater Lake’s native fauna will be a challenge for park resource managers.