An Assessment of the Effects of Zebra Mussel Presence on Clam Health: a case study in Five Northern Michigan Lakes

Abstract

Zebra mussel presence in the waterbodies of the Great Lakes Region continues to have large effects on the aquatic ecosystems they inhabit, specifically in relation to a decrease in unionid clam populations. We performed a study to determine how zebra mussels impact clam health, which we evaluated based on the mass and length of the clams. We surveyed five lakes: Larks Lake and Wycamp Lake, which have no zebra mussels, Douglas Lake and Burt Lake, which still contain zebra mussels, and Round Lake, which has zebra mussels but has been treated with Zequanox to control the zebra mussel population. At each lake, we collected clams and recorded their weight, using a 100-gram spring scale, and length, using a manual caliper. Looking at the weight versus length of each lake, Larks Lake had the steepest slope (m = 17.64), while Round Lake had the smallest slope (m = 10.30) (Fig. 1). The lengths of the smallest clams in each lake were significantly different from each other except for Larks and Douglas Lake (p-value = .294) (Table 1). The lengths of the largest clams in each lake showed more variation – Round and Douglas Lake, Wycamp and Larks Lake, and Wycamp and Round Lake did not have large clam lengths that were significantly different from each other (p = .761, p = .834, p = .090) (Table 2). Using weight versus length as a measure of clam health, we concluded that clams in lakes without zebra mussel presence were healthier than clams in lakes with continued zebra mussel presence. Our data suggest that this invasive species of mollusc has detrimental effects on native unionid clams in inland lakes in northern Michigan.