Unionid Mussels from Nearshore Zones of Lake Erie

Concern exists that the introduction of dreissenid mussels following long-term effects of pollution may have completely eliminated native mussel species from Lake Erie. Natural seiche events were used to facilitate surveys for live unionids on five occasions in the western basin of Lake Erie and Sandusky Bay between 2007 and 2009, and beach and estuary surveys were conducted at numerous additional sites between 2004 and 2009. Sixteen unionid species were found living in or near Lake Erie, including six sites in the nearshore zone of the lake. Each community consisted of live individuals from two to eight species, and evidence included live and/or fresh dead material from several state listed species at multiple sites. Where estimated, the mean overall density was low at 0.09 unionids/m2, although similar to other known unionid refuges in the lower Great Lakes. While the ephemeral nature of seiche events makes them a limited survey tool, their application combined with increasing numbers of fresh shells washing ashore over the past few years indicates that unionids are extant in the western basin of Lake Erie, and may further suggest that conditions may be improving for native mussel species

Modeling Habitat of Freshwater Mussels (Bivalvia:Unionidae) in the Lower Great Lakes 25 Years after the Dreissena Invasion

Finding remnant populations of species that are of conservation concern can be difficult, particularly in aquatic habitats. Models of ecological niches can aid in the discovery of refuges. Remnant populations of native freshwater mussels (unionids) have been found in Lakes Erie and St Clair. Our goals were to predict undiscovered refuges in Lake Ontario based on habitat analysis from Lake Erie and to conduct surveys to test those predictions. We built a presence-only model on environmental data including attributes of the benthic zone and shoreline where mussels occurred in Lake Erie. We found a link between small- and large-scale variables related to unionid persistence. Bathymetry, fetch, and shoreline geomorphology contributed most to the model. These variables correspond to local-scale environmental factors important for unionid survival, including presence of vegetation and substrate composition, which explained ∼22% of the variance in presence, abundance, and richness. The model predicted that 0.8% of the near-shore area of Lake Ontario should be habitat for unionids. In surveys at 34 locations on the USA shore of Lake Ontario, we found 1800 unionids of 11 species and showed that areasOntario, a result signifying generality of our model for conservation approaches to freshwater mussels

Competitive Replacement of Invasive Congeners May Relax Impact on Native Species: Interactions among Zebra, Quagga, and Native Unionid Mussels

Determining when and where the ecological impacts of invasive species will be most detrimental and whether the effects of multiple invaders will be superadditive, or subadditive, is critical for developing global management priorities to protect native species in advance of future invasions. Over the past century, the decline of freshwater bivalves of the family Unionidae has been greatly accelerated by the invasion of Dreissena. The purpose of this study was to evaluate the current infestation rates of unionids by zebra (Dreissena polymorpha) and quagga (D. rostriformis bugensis) mussels in the lower Great Lakes region 25 years after they nearly extirpated native unionids. In 2011–2012, we collected infestation data for over 4000 unionids from 26 species at 198 nearshore sites in lakes Erie, Ontario, and St. Clair, the Detroit River, and inland Michigan lakes and compared those results to studies from the early 1990s. We found that the frequency of unionid infestation by Dreissena recently declined, and the number of dreissenids attached to unionids in the lower Great Lakes has fallen almost ten-fold since the early 1990s. We also found that the rate of infestation depends on the dominant Dreissena species in the lake: zebra mussels infested unionids much more often and in greater numbers. Consequently, the proportion of infested unionids, as well as the number and weight of attached dreissenids were lower in waterbodies dominated by quagga mussels. This is the first large-scale systematic study that revealed how minor differences between two taxonomically and functionally related invaders may have large consequences for native communities they invade

Unionid Mussels from Nearshore Zones of Lake Erie

Concern exists that the introduction of dreissenid mussels following long-term effects of pollution may have completely eliminated native mussel species from Lake Erie. Natural seiche events were used to facilitate surveys for live unionids on five occasions in the western basin of Lake Erie and Sandusky Bay between 2007 and 2009, and beach and estuary surveys were conducted at numerous additional sites between 2004 and 2009. Sixteen unionid species were found living in or near Lake Erie, including six sites in the nearshore zone of the lake. Each community consisted of live individuals from two to eight species, and evidence included live and/or fresh dead material from several state listed species at multiple sites. Where estimated, the mean overall density was low at 0.09 unionids/m2, although similar to other known unionid refuges in the lower Great Lakes. While the ephemeral nature of seiche events makes them a limited survey tool, their application combined with increasing numbers of fresh shells washing ashore over the past few years indicates that unionids are extant in the western basin of Lake Erie, and may further suggest that conditions may be improving for native mussel species

Numbers and wet weight of all attached dreissenids (>2 mm in size) and separately by species (<i>Dreissena polymorpha</i> and <i>D. rostriformis bugensis</i>) per infested host unionid (mean ± standard error, median, lower and upper quartiles, sample size) in studied lakes in 2011–2012.

<p>Numbers and wet weight of all attached dreissenids (>2 mm in size) and separately by species (<i>Dreissena polymorpha</i> and <i>D. rostriformis bugensis</i>) per infested host unionid (mean ± standard error, median, lower and upper quartiles, sample size) in studied lakes in 2011–2012.</p

Distribution of Native Mussel (Unionidae) Assemblages in Coastal Areas of Lake Erie, Lake St. Clair, and Connecting Channels, Twenty-five Years After a Dreissenid Invasion

Over the past 25 years, unionid mussels in the Laurentian Great Lakes of North America have been adversely impacted by invasive dreissenid mussels, which directly (e.g., by attachment to unionid shells) and indirectly (e.g., by competing for food) cause mortality. Despite the invasion, unionids have survived in several areas in the presence of dreissenid mussels. We investigated current spatial patterns in these native mussel refuges based on surveys for unionid mussels across 48 sampling locations (141 sites) in 2011 and 2012, and documented species abundance and diversity in coastal areas of lakes St. Clair and Erie. The highest-quality assemblages of native mussels (densities, richness, and diversity) appear to be concentrated in the St. Clair delta, where abundance continues to decline, as well as in in Thompson Bay of Presque Isle in Lake Erie and in just a few coastal wetlands and drowned river-mouths in the western basin of Lake Erie. The discovery of several new refuge areas suggests that unionids have a broader distribution within the region than previously thought

Infestation of unionids by <i>Dreissena</i> spp. in the waterbodies surveyed in 2011–2012.

<p>Percent unionids infested by dreissenid mussels, the ratio of total wet weight of attached <i>Dreissena</i> spp. (>2 mm in size) to host unionid wet weight (mean ± standard error, median, lower and upper quartiles, sample size in parentheses), percent unionids with past infestation (unionids with or without <i>Dreissena</i> and with byssal threads) and percent <i>D. polymorpha</i> of total lake-wide dreissenid abundance are given for each waterbody studied (the lower Great Lakes, Lake St. Clair, the Detroit River, and inland lakes in north Michigan (Burt, Douglas, and Paradise lakes)).</p>a<p>Time since the first recorded finding. No <i>D. r. bugensis</i> was reported from lakes Burt, Douglas and Paradise.</p>b<p>D. Zanatta, unpublished data.</p><p>Infestation of unionids by <i>Dreissena</i> spp. in the waterbodies surveyed in 2011–2012.</p

Infestation parameters of unionids by species collected from waterbodies dominated by zebra or quagga mussels.

<p>Proportion of unionids infested by dreissenids by unionid species, proportion of unionids with evidence of past infestation (regardless of <i>Dreissena</i> presence), <i>Dreissena</i> spp./host unionid wet weight ratios, and the proportion of uninfested unionids of those with past infestation in waterbodies dominated by <i>D. polymorpha</i> (Lake St. Clair, the Detroit River, Paradise, Douglas and Burt lakes in Michigan, magenta bars) and in lakes Erie and Ontario dominated by <i>D. r. bugensis</i> (purple bars).</p

Map of sampling locations surveyed in 2011–2012.

<p>Each nearshore location (dots) was sampled at several (from 1 to 5) standard collection sites (0.5 ha surveyed for two person hours of search time). The inset gives sampling locations in inland Michigan lakes (Burt, Douglas, and Paradise).</p