DIVERSITY AND ABUNDANCE OF TERRESTRIAL GASTROPODS IN VOYAGEURS NATIONAL PARK, MN: IMPLICATIONS FOR THE RISK OF MOOSE BECOMING INFECTED WITH PARELAPHOSTRONGYLUS TENUIS

Abstract

Voyageurs National Park (VNP) has a stable population of about 40–50 moose (Alces alces). Recent declines in moose abundance in adjacent areas in northern Minnesota raise concerns about the long-term viability of moose in VNP. The parasitic nematode Parelaphostrongylus tenuis has been documented in moose in VNP and has been implicated in moose declines in other populations. Terrestrial gastropods are the intermediate hosts for P. tenuis, and describing spatial and temporal differences in their abundance should increase understanding about the risk of P. tenuis infection for VNP moose at the individual and population levels. We used cardboard sheets to estimate species composition and abundance of terrestrial gastropods in representative vegetation communities in VNP. We collected a total of 6,595 gastropods representing 25 species, 22 terrestrial snails and 3 slugs; 8 are known vectors of P. tenuis, including the slug Deroceras laeve, the most common species found. Gastropods were more abundant in September than July, and in upland forests (maximum = 555 gastropods/m²) more than in wetter lowlands (20 gastropods/m²). We used location data from GPS collared moose in VNP to estimate the relative exposure of moose to gastropods that could be infected with P. tenuis larvae. The boreal hardwood forest and northern spruce-fir forest ecotypes had the highest use by moose and high abundance of P. tenuis vectors in summer, and may pose the greatest risk for infection. Habitat use and the related risk of ingesting gastropod vectors varied by individual moose. Our method can be extended in moose range to estimate the relative risk of P. tenuis infection.