AUTHORS: Jeremy Hartsock, Michigan State University, Department of Fisheries and Wildlife; Dan Hayes, Michigan State University, Department of Fisheries and Wildlife; Jo Latimore, Michigan State University, Department of Fisheries and Wildlife; Erick Elgin, Michigan State University Extension
ABSTRACT: Submersed macrophytes strongly influence the structure and function of inland lakes. However, quantitative data are broadly lacking on the distribution and abundance of aquatic macrophytes in northern Michigan. To fill these knowledge gaps, we performed macrophyte surveys at 75 inland lakes in the Northern Lake Huron and Eastern Lake Superior management units using a modified point-intercept survey approach whereby a double sided rake was tossed twice at each sampling point (~100 points sampled per lake). Among all lakes surveyed a total of 60 macrophyte species were observed. Chara sp. was the most frequently encountered macrophyte. The most species rich lake contained 32 species and the most species poor contained 3 species. Of note, we detected aquatic invasive species (AIS) in nearly half of the lakes surveyed. Invasive watermilfoil and starry stonewort were the most frequently observed AIS. An occupancy analysis revealed that a single rake toss approach underestimates the true occurrence of aquatic macrophytes due to incomplete detection probability. We also show that a single rake toss approach yields similar estimates of species richness but requires more points to be sampled than a two rake toss approach. Our experience is that approximately 100 points could be sampled per day with a two rake toss approach, yielding observed species richness close to predicted richness, and providing reasonable precision of estimates of coverage for common species. Future research will focus on comparing our modified PI survey to other macrophyte survey approaches.
