Long-term changes in distribution and abundance of submerged aquatic vegetation and dreissenid mussels in Long Point Bay, Lake Erie

Submerged aquatic vegetation (SAV) in Inner Long Point Bay (LPB), Lake Erie provides food and habitat for a diversity of fish and wildlife. The abundance and community structure of SAV often are used as bioindicators of ecosystem health. Colonization and increases in abundance of zebra mussels (Dreissena polymorpha) at LPB in the early 1990s increased water clarity which changed the SAV community. We used data from studies in 1976, 1991, and 1992 and sampled LPB in 2009 to quantify changes in abundance and occurrence of SAV, determine densities of zebra mussels, and model influences of year, water depth and substrate type on the probability of detection of SAV. We detected 96% decrease in mean (± SE) mussels/m2 between 1992 (457 ± 86) and 2009 (19 ± 2). With the exception of slender pondweed (Potamogeton pusillus), the five most abundant SAV species in 1992 had decreased by 2009. Water depth and substrate type influenced probability of detection of all SAV species, excluding Najas spp., suggesting that changes in Lake Erie water levels and sediment loading may influence future SAV communities. Decreased abundance of filter feeding mussels is consistent with increased eutrophication and changes in SAV in LPB. Carrying capacity of LPB for waterfowl and other fish and wildlife that use and eat SAV and mussels increased during the mid-1990s, but has since decreased.