Invasion of North American waters by Dreissena polymorpha and D. rostriformis bugensis has resulted in declines in native North American Unionoida mussels. Dreissenid mussels biofoul unionid mussels in large numbers and interfere with unionid movement, acquisition of food and ability to open and close their shells. Initial expectations for the Great Lakes were that unionids would be extirpated where they co-occur with dreissenids, but recently adult and juvenile unionids have been found alive in several apparent refugia. These unionid populations may persist due to reduced dreissenid biofouling in these areas, and/or due to processes that remove biofoulers. For example, locations inaccessible to veligers may reduce biofouling and habitats with soft substrates may allow unionids to burrow and thus remove dreissenids. Here, biofouling was measured by deploying caged unionid mussels (Lampsilis siliquoidea) at 36 sites across the western basin of Lake Erie to assess spatial variation in biofouling and to identify other areas that might promote the persistence or recovery of native unionid mussels. Biofouling ranged from 0.03 – 26.33 g per mussel, reached a maximum in the immediate vicinity of the Maumee rivermouth, and appeared to primarily consist of dreissenid mussels. A known mussel refugium in the vicinity of a power plant near the Maumee rivermouth actually exhibited very high biofouling rates, suggesting low dreissenid colonization is unlikely to be the primary cause of unionid survival in this refugium. The southern nearshore area of Lake Erie, near another refugium, also had very low biofouling. A large stretch of the western basin appeared to have low biofouling rates and muddy substrates, raising the possibility that these open water areas could support remnant and returning populations of unionid mussels.

Many taxa of North American unionid mussels are imperiled due to biofouling by invasive dreissenid mussels. Here, we report on biofouling rates of unionid mussels suspended in cages during the growing season in nearshore embayments in Lake Erie (2013-2016), Lake Michigan (Green Bay 2016, Grand Traverse Bay 2015) and Lake Huron (Saginaw Bay 2015). Mussels were deployed in early summer (late May or early June) and retrieved in late summer or fall (late August or early September). Wet weights were collected from mussels before and after removal of biofouling taxa (primarily dreissenid mussels).

Many taxa of North American unionid mussels are imperiled due to biofouling by invasive dreissenid mussels. Here, we report on biofouling rates of unionid mussels suspended in cages during the growing season in nearshore embayments in Lake Erie (2013-2016), Lake Michigan (Green Bay 2016, Grand Traverse Bay 2015) and Lake Huron (Saginaw Bay 2015). Mussels were deployed in early summer (late May or early June) and retrieved in late summer or fall (late August or early September). Wet weights were collected from mussels before and after removal of biofouling taxa (primarily dreissenid mussels).

Data is included for two types of field surveys conducted for freshwater mussels in the mainstem of the middle and upper Delaware River in the Mid-Atlantic region of the United States from 2000-2002. Timed search (qualitative) surveys were conducted during 2000-2001 from a point at the confluence of the East and West Branches of the Delaware River near Hancock, NY continuously downstream to a point at the mouth of the Paulins Kill River near Columbia, NJ. In this qualitative survey, mussel species and counts were collected in the field catch-per-unit-effort (CPUE) data was determined for all mussel species within each of 1,095 consecutive stream sections ~200 m in length. Subsequent quantitative surveys were conducted in select 200-m sections of river using quadrats during 2002 in order to estimate abundance and density of mussel present in these sections. One Excel file contains data from qualitative surveys, and a second excel file contains data from quantitative quadrat surveys.

Data is included for two types of field surveys conducted for freshwater mussels in the mainstem of the middle and upper Delaware River in the Mid-Atlantic region of the United States from 2000-2002. Timed search (qualitative) surveys were conducted during 2000-2001 from a point at the confluence of the East and West Branches of the Delaware River near Hancock, NY continuously downstream to a point at the mouth of the Paulins Kill River near Columbia, NJ. In this qualitative survey, mussel species and counts were collected in the field catch-per-unit-effort (CPUE) data was determined for all mussel species within each of 1,095 consecutive stream sections ~200 m in length. Subsequent quantitative surveys were conducted in select 200-m sections of river using quadrats during 2002 in order to estimate abundance and density of mussel present in these sections. One Excel file contains data from qualitative surveys, and a second excel file contains data from quantitative quadrat surveys.

We conducted large-scale systematic surveys for native mussels across six reaches of the upper Mississippi River. In each reach, divers placed two 0.25 square meter quadrat frames on the river bottom. The duplicate quadrats, which were placed 10 m apart in an upstream to downstream direction, were used to increase the area sampled at each site and increase the effectiveness of this cluster design. Divers excavated substrates to a depth of about 15 cm and placed material into a 6 mm mesh bag. Mussels were identified to species, aged via external annuli, measured for shell length, and sexed (in species with external sexual dimorphism).

Spectaclecase (Margaritifera monodonta) is a federally endangered freshwater mussel species that has experienced a 55% reduction in range (USFWS 2014) and is currently concentrated in three rivers in the Midwest of the United States (Gasconade, Meramec Rivers, MO, and St. Croix River, WI). Its preference for living under large rocks and boulders has limited detection of new populations by traditional survey methods. Environmental DNA technology has been used to detect invasive and rare species, but its use for detection of rare, benthic-dwelling species in large flowing systems has been limited. Here, we propose using environmental DNA to identify presumable sites for discovery of M. monodonta. We designed a M. monodonta-specific qPCR assay and tested it using M. monodonta-housed tank water and water samples from two known mussel beds on the St. Croix River and three known mussel beds on the Mississippi River. We observed higher overall detection rate on the St. Croix River (30.2%) compared to the Upper Mississippi River (0.60%). We also observed higher eDNA detection rates (73.3-93.1%) in 2018 for samples collected during the larval release period in May compared to samples collected in August after reproduction stopped (55.6-70.8%) on the St. Croix River. We tested samples collected at three distances downstream of the two mussel beds found in the St. Croix River, but we did not observe a significant effect of distance on our detection rates. However, we did observe greater detection rates for samples collected near the bottom compared to at the surface. Our results indicate that this novel qPCR assay can successfully detect M. monodonta eDNA and could be utilized to rapidly screen locations to guide intensive physical searches for populations in riverine systems.

Spectaclecase (Margaritifera monodonta) is a federally endangered freshwater mussel species that has experienced a 55% reduction in range (USFWS 2014) and is currently concentrated in three rivers in the Midwest of the United States (Gasconade, Meramec Rivers, MO, and St. Croix River, WI). Its preference for living under large rocks and boulders has limited detection of new populations by traditional survey methods. Environmental DNA technology has been used to detect invasive and rare species, but its use for detection of rare, benthic-dwelling species in large flowing systems has been limited. Here, we propose using environmental DNA to identify presumable sites for discovery of M. monodonta. We designed a M. monodonta-specific qPCR assay and tested it using M. monodonta-housed tank water and water samples from two known mussel beds on the St. Croix River and three known mussel beds on the Mississippi River. We observed higher overall detection rate on the St. Croix River (30.2%) compared to the Upper Mississippi River (0.60%). We also observed higher eDNA detection rates (73.3-93.1%) in 2018 for samples collected during the larval release period in May compared to samples collected in August after reproduction stopped (55.6-70.8%) on the St. Croix River. We tested samples collected at three distances downstream of the two mussel beds found in the St. Croix River, but we did not observe a significant effect of distance on our detection rates. However, we did observe greater detection rates for samples collected near the bottom compared to at the surface. Our results indicate that this novel qPCR assay can successfully detect M. monodonta eDNA and could be utilized to rapidly screen locations to guide intensive physical searches for populations in riverine systems.

A systematic sampling design was developed to sample mussels in Upper Mississippi River navigation Pools 3, 5, 6, 8, 13 and 18. Hydrologically-enforced buffers were created at a hierarchy of scales to better determine the extent of influence on mussel population assemblages. Buffers were generated using a radii of 10 meters from the quadrat site point. Several landscape metrics related to the buffer shape, underlying water depth at several modeled river discharges, aquatic vegetation presence, river training structure presence, topographic position, aquatic area classification, adjacent land use types, and wind fetch magnitude were then calculated to help assess which of these metrics/indices are predictive of the distribution, abundance, diversity, and recruitment of native mussels across these six pools in the Upper Mississippi River.

A systematic sampling design was developed to sample mussels in Upper Mississippi River navigation Pools 3, 5, 6, 8, 13 and 18. Hydrologically-enforced buffers were created at a hierarchy of scales to better determine the extent of influence on mussel population assemblages. Buffers were generated using a radii of 1000 meters from the quadrat site point. Several landcape metrics related to the buffer shape, underlying water depth at several modeled river discharges, aquatic vegetation presence, river training structure presence, topographic position, aquatic area classification, adjacent land use types, and wind fetch magnitude were then calculated to help assess which of these metrics/indices are predictive of the distribution, abundance, diversity, and recruitment of native mussels across these six pools in the Upper Mississippi River.