Habitat characteristics of a unionid refuge in the thermal plume of a power plant in western Lake Erie

We examined habitat characteristics to determine why a rich community of unionid mussels lives in the thermal plume of the Bayshore Power Plant, Oregon Ohio. We expected to find that the power plant reduced the density and viability of dreissenid veligers and that the depth and organic matter content of sediments in the thermal outflow were greatest near the plant. Water temperature averaged 3.8 +/- 1.5 degrees C warmer at the plant's outflow than intake, and the ratio of live:dead veligers was significantly lower at the outflow than intake on most dates (P <= 0.05). A laboratory experiment confirmed that heating water comparable to passing through the power plant significantly reduced veliger viability (P <= 0.01). However, wind direction affected the differences in veliger density between the intake and outflow (P <= 0.01), with easterly winds (opposing the direction of discharge) increasing the density of veligers at the outflow. Similarly, water temperature declined with distance from the plant, but east winds increased variations in water temperatures. Apparently wind direction facilitates (westerly) or slows (easterly) the discharge of water from the small embayment receiving the power plant's thermal effluent. Particulate organic matter content of the thermal plume varied with wind speed, apparently due to suspension of sediments in this shallow water. Finally, only the coarse (>10 mm) size fraction of the benthic sediments was related to distance from the power plant. Thus the thermal regime of this habitat appears to be the primary explanation for this unionid refuge. (C) 2014 International Association for Great Lakes Research. Published by Elsevier B.V. All rights reserved.