A refuge for native freshwater mussels (Bivalvia: Unionidae) from impacts of the exotic zebra mussel (Dreissena polymorpha) in Lake St. Clair (original) (raw)
The introduction and spread of the exotic zebra mussel (Dreissena polymorpha) throughout the Great Lakes has decimated native unionid populations. However, significant communities have continued to survive in several nearshore areas of Lake Erie. This study documents the discovery of a "refuge" site for unionids in Lake St. Clair. Ninety-five sites in various areas around the lake were surveyed between 1998 and 2001, and 2,356 live unionids of 22 species were found alive at 33 of these sites. Almost all sites (31) were in shallow (mainly < 1 m) waters of the St. Clair delta, in habitats similar to refugia in Lake Erie, i.e., nearshore areas with firm sandy substrates and marshy bays with soft, muddy sediments. Species richness ranged from 1 to 12 species per site, and relative abundance ranged from 2 to 302 unionids per person-hour of sampling effort. Densities at nine sites ranged from 0.03 to 0.07 per m 2 . Five species considered to be at risk were found alive. Infestation rates at sites near the St. Clair delta ranged from 0 to 286 zebra mussels per unionid, which is slightly higher than rates at other known refuge sites. The community is now dominated by thick-shelled species such as Fusconaia flava and Lampsilis cardium, which are known to be least susceptible to zebra mussels. Further studies are needed to determine if unionid populations in the delta are stable, and to understand the mechanisms responsible for unionid survival at this and other refugia. Such information could be used to predict the locations of other natural sanctuaries and to guide their management for the preservation of the Great Lakes unionid fauna.
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Characteristics of a refuge for native freshwater mussels (Bivalvia: Unionidae) in Lake St. Clair
Journal of Great Lakes Research, 2009
The Lake St. Clair delta (∼ 100 km 2 ) provides an important refuge for native freshwater mussels (Unionidae) wherein 22 of the ∼ 35 historical species co-occur with invasive dreissenids. A total of 1875 live unionids representing 22 species were found during snorkeling surveys of 32 shallow (∼ 1 m) sites throughout the delta. Richness and density of unionids and zebra mussel infestation rates varied among sites from 3 to 13 unionid species, 0.02 to 0.12 unionids/m 2 , and b 1 to 35 zebra mussels/unionid, respectively. Zebra mussel infestation of unionids in the delta appears to be mitigated by dominant offshore currents, which limit densities of zebra mussel veligers in nearshore compared to offshore waters (13,600 vs. 28,000/m 3 , respectively). Glycogen concentrations in the tissues of a common and widespread species in the delta (Lampsilis siliquoidea) suggest that zebra mussels may be adversely affecting physiological condition of unionids in a portion of the Lake St. Clair delta. Physiological condition and community structure of unionids within the delta may also be influenced by differences in food quantity and quality resulting from the uneven distribution of water flowing from the St. Clair River. The delta likely supports the largest living unionid community in the lower Great Lakes and includes several species that have been listed as Endangered or Threatened in Canada and/or the state of Michigan, making it an important refuge for the conservation of native unionids.
Northeastern Naturalist, 2015
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.
Diversity and Distributions, 2011
Aim Geographic patterns of species distributions and the factors contributing to species endangerment are necessary for the development of integrative conservation strategies. Freshwater mussels Unionidae have among the highest levels of imperilment recorded in North America. This paper describes the biogeography and diversity of Unionidae along climate and habitat gradients in Texas, evaluates human impact, and identifies the hot spots of diversity and endemism that should be targeted for conservation. Location Texas, North America. Methods Unionids were surveyed in all major Texas river basins in 2003-2009. Multivariate statistics were used to test for differences in environmental parameters and among unionid assemblages in different bioprovinces, and to determine to what extent the multivariate pattern of species distribution was affected by environmental factors. To estimate human impact, we examined the relationship between human population density and the proportion of rare species, as well with the proportion of historically present species that persist in the watershed. Results Correlation between biotic and environmental similarity matrices indicated concordance in the differences among unionid assemblages and environmental factors that could cause these differences. Lake surface evaporation rate and percentage of forest cover in the watershed were among the most important parameters explaining the differences in unionid assemblages. Human population density was negatively correlated with the proportion of rare species. The proportion of species found live relative to the total number of live and relic species found in our surveys and to the number of historically known species decreased with the increase in human population density. Main conclusions Climate, landscape, geology, and land use type were important factors influencing unionid distribution patterns among biotic provinces. Increased human population density was associated with the loss of rare species over several decades, but this loss was not recognized because of a lack of assessing the conservation status of unionids.
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Survival of Unionids Following Removal of Attached Zebra Mussels
Journal of Freshwater Ecology, 2001
A mussel mark-recapture study was initiated in the upper Mississippi River, Wisconsin, to measure the survival of Elliptio dilatata colonized by Dreissena polymorpha in Lake Pepin, Mississippi River. In 1996,240 adult E. dilatata were marked in Lake Pepin. At the time of marking we cleansed zebra mussels from 48 of the 240 E. dilatata to test if a one-time removal of D. polymorpha would be effective in improving survival of E. dilatata. In 1997, 1998, and 1999, marked mussels were recovered and identified; survival was determined; and live individuals were returned to the mussel bed. Mean annual survival of E. dilatata cleaned of D. polymorpha equaled 94 ' 3.0% and was not significantly different from those not cleaned (89 ' 1.7%) (xZ ,,-, =2.3 1, p=0.13). The mean number of D. polynzorpha colonized upon cleaned and uncleaned E. dilatata at the conclusion of this study in 1999 equaled 105.8 ' 12.9 and 94.6 ' 8.4 respectively (p>0.05). Since survival rates and the abundance of D. polymorpha on the two groups of E. dilatata were not significantly different following the years after initial cleaning, we suggest that a one time removal of D. polymorpha from native mussels is not a biologically effective management tool.
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