Effects of Water Level Fluctuations on Zebra Mussel Distribution in a Lake Erie Coastal Wetland

ABSTRACT

In May–August 2002, we examined how seasonal water level changes and frequent wind-driven seiches limited the amount of habitat for zebra mussels (Dreissena polymorpha) in a Lake Erie coastal wetland. We counted numbers of veligers that colonized artificial substrates at different depths (1–17 cm, 18–34 cm and >34 cm below the water surface). Water levels decreased during the summer, and by August colonization plates set at 1–17 cm were exposed 85% of the time, plates set at 18–34 cm were exposed 15% of the time, but plates set at >34 cm were rarely exposed. The highest densities (numbers/m²) of colonization occurred in June (7176.1) and August (3119.5), and this bimodal pattern has been observed in other Great Lake habitats. Densities were highest at >34 cm depths (5552.7), intermediate at 18–34 cm (2802.1) and lowest at 1–17 cm (410.8). Veliger numbers on some plates in deep water levels were as high as 10,000/m², which are similar to densities in the Great Lakes. We also measured survivorship of adult mussels in wire mesh cages from 28 July to 25 August. Most (~90%) adult zebra mussels survived in both 18–34 cm and >34 cm water levels, but only ~2% survived in 1–17 cm water levels. We determined the percent of Crane Creek Marsh in each of the three water depth zones and estimated that water level changes prevent zebra mussels from inhabiting 62% of this coastal wetland. The low survival of zebra mussels may be a reason why abundant unionids have recently been found in this and some other Great Lake coastal wetlands.