Zebra Mussel Habitat Selection, Growth and Mortality in Lakes of Northeastern Wisconsin and the Upper Peninsula of Michigan

Abstract

Invasive zebra mussels (Dreissena polymorpha) have been anthropogenically transported to various inland locations in the midwestern United States from the Laurentian Great Lakes. In northeastern Wisconsin and the Upper Peninsula of Michigan, additional colonization is occurring along natural corridors and by inadvertent human transport. High fecundity and filtering rates of zebra mussels and the ability to attach to substrates cause tremendous ecological and economic impacts. Because management options are limited once zebra mussels become established, there is a critical need to contain their spread. Identifying characteristics of new “source” population invasions may assist early detection monitoring efforts. Suitability models based on water calcium concentrations are currently used to identify lakes in which to focus pre-invasion monitoring efforts. Understanding lake-specific habitat limitations could refine monitoring efforts by identifying locations within lakes that have the greatest establishment potential. Additionally, quantitative comparisons of zebra mussel growth and mortality among lakes across a range of colonization periods may provide information to managers and landowners on anticipated population trajectories following establishment. The objectives of this study were to: (1) determine if habitat selection by zebra mussels occurs within lakes; (2) determine if differential habitat selection occurs among lakes consistent with time since colonization and, if so, build a predictive model of potential habitat use; (3) determine if zebra mussel mean length-at-age and mortality rates differ among sampled populations. SCUBA diving was used to sample 10 quadrats at regular intervals along 12 transects (120 total quadrats) representing a variety of habitats in eight lakes. Within quadrats, water depth was measured and substrates were visually estimated to quantify habitat availability. Zebra mussel presence / absence were recorded for available substrates in each quadrat. Selection indices were used to evaluate zebra mussel habitat selection. Zebra mussels were randomly collected from one quadrat along each transect. Length and age for each collected individual was used to evaluate zebra mussel mean length-at-age and mortality. Von Bertalanffy growth curves were estimated to determine whether zebra mussel mean length-at-age varied among lakes and catch curves were used to determine whether zebra mussel mortality rates varied among lakes. Results suggest that zebra mussels selected for hard substrates (i.e., rock, wood, and shells), avoided soft substrates (i.e., silt, particulate, and sand), and used macrophytes in proportion to availability. Zebra mussel growth varied among lakes and there was no difference in zebra mussel mortality rates among lakes. Current monitoring efforts focus on veliger tows or substrate samplers which are effective only after a population is widely established. These results can be applied to early detection monitoring protocols to detect a pioneer zebra mussel population. Few studies have evaluated zebra mussel mean length-at-age and mortality in North America and this study can be used as a template to evaluate mean length-at-age and mortality across a variety of lakes to increase our understanding of zebra mussel biology.