( subviridis)

Green Floater, credit USGS The green floater is a freshwater that has declined precipitously in population size and distribution over the last 100 years, and is now vulnerable to extinction. Land use changes have increased erosion and sediment runoff, reducing water quality, and harming . The green floater was petitioned for Federal listing under the Endangered Act in 2010 and the American Fisheries Society classified it as threatened in 1993. Historically, they were present in 10 states (, , , , West , Virginia, Tennessee, , Georgia, and Alabama) and the District of Columbia (Figure 1). They are now extirpated in two states and the District of Columbia and have had significant declines in abundance and presence in other states (NatureServe 2020). In Maryland, this species is present in only a few watersheds.

The green floater is small, typically less than 55 millimeters (mm) in length. It has a subovate or trapezoidal shape and a thin yellowish-brown shell covered in varying amounts of green rays. Younger specimens are typically greener (PNHP 2012). The green floater is also distinct for its interior shell color of whitish to blue, and an interdental tooth. The small size and low abundance of this species can make it more difficult to find during surveys. More research is needed to obtain additional information regarding ecology, genetics, and life history (USGS 2019).

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Figure 1. This 2020 map demonstrates the distribution of the green floater mussel from Alabama to New York (NatureServe 2020).

LIFE HISTORY Like other freshwater mussels, sexual reproduction occurs through the water column. Male specimens discharge sperm into the water, and females passively filter water through the gills where eggs are fertilized and develop into the larval stage called glochidia. This fertilization process typically occurs in mid-summer to fall. However, unlike most freshwater mussel species, green floaters are also known to be hermaphroditic, meaning that female mussels can self- fertilize. For many freshwater mussels, the glochidia are released the following spring-summer back into the water column, where they attach to a host fish for dispersal. The larvae transform on the host fish’s gills into the juvenile stage, before dropping to the river bottom, where they then grow to full-sized adults. Green floaters are thought to use this strategy but also have another strategy, unique among Unionid mussels for reproduction. Green floaters have the ability to transform glochidia to juveniles in their gills without a host fish. Juvenile green floaters are released from the female’s gills fully formed as juvenile mussels. While direct transformation is thought to be used more commonly by green floaters and allows them to reproduce with no need of a host fish, it only allows for downstream dispersal. Attachment of larvae to host fish is the sole method for upstream dispersal. More research is needed to determine the frequency of self- fertilization, juvenile transformation in the gills, and use of host fish. The lifespan of green floaters is quite short, ranging from 3 to 7 years, with an average of 4 years (DECNY 2014).

HOST FISHES For most other freshwater mussel species, host fishes are necessary to complete the reproductive cycle of the mussel for dispersal of larvae. However, the green floater is unique in that it does not

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require a host fish. Juveniles are instead able to form in the adult female mussel. However, in a host fish study conducted by Jones (USFWS, unpublished data), green floater larvae successfully metamorphosed to juveniles while attached to five of the six species tested: (Cottus bairdii), rock bass (Ambloplites rupestris), central stoneroller (Campostoma anomalum), blacknose dace (Rhinichthys atratulus), and margined madtom (Noturus insignis). Research is still ongoing to identify if their self-sufficient reproductive cycle is typical or if they occasionally use host fish in the wild (USGS 2019).

HABITAT Green floaters occupy slow running streams and rivers and can sometimes be found in pool habitat. The green floater is not often found in strong currents. They can be found in a variety of different flowing-water systems, but are more likely to be found where there is stable, fine substrate particles including gravel, sand, and silt (USGS 2019). They are found in backwater or side channels in larger rivers. They require well oxygenated water systems with clean silt, little pollution, and of depths between 1 to 4 feet. They are therefore particularly susceptible to changes in land use that may cause increases in water flow or sediment (DECNY 2014).

One challenge with this species is lack of reliability in some historical records. The estimates of historic range are most likely quite conservative, and it is likely that there were historically additional populations in states not mentioned prior such as Delaware, Kentucky, South Carolina, and Ohio. However, unconfirmed records have been debated as misidentifications, possibly (Lasmigona decorata) or creek heelsplitter (), which are similar in appearance. Additionally, some creeks and streams were not sampled until after declines were noted, making it possible they were extirpated instead of absent (NatureServe 2020).

Today over 50 percent of confirmed populations are extirpated. Populations that are extant are dwindling in size and have poor viability. Most sites have on average 1 to 5 live individuals. It is also important to note that biannual surveying of all sites would be beneficial to continue documenting presence, as many sites are not surveyed regularly enough to maintain an understanding of their population size. Two years is frequent enough to gain knowledge, while preventing disturbance from survey efforts (NatureServe 2020).

MARYLAND POPULATIONS Maryland green floater populations were historically prominent throughout the Upper, Middle, and Washington Metro area of the Potomac River, as well as tributaries in the larger Potomac River watershed throughout Allegany, Washington, Fredrick, Montgomery, and Carroll Counties (Figure 2). It is likely that this species was once prominent in other creeks nearby that were never surveyed, making its historical range larger than previously thought (CBWP 2016).

Survey efforts in the early 2000s depicted population declines and extirpation or presumed extirpation. The few extant populations remaining were small, isolated, and scattered. Most recently, the green floater has been documented in the Potomac River in both Washington and Montgomery Counties, however only one specimen was found at each site. Outside the Potomac River, there are only two recently documented extant populations remaining, Sideling Hill and Licking Creek (USFWS SSA 2020).

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In September of 2019, Sideling Hill Creek and Licking Creek were surveyed. In Sideling Hill Creek watershed, 25 sites were surveyed where green floaters have been found in the past. Of those 25 sites, only 2 sites had green floaters, and only 11 total specimens were found. This is down from 56 total specimens found in 2006 across 6 sites, though it is worth noting that not all sites were resampled, there were some new sites, and some landowners did not give permission to survey (McCann and Feller 2020).

In Licking Creek 13 sites were sampled. Results demonstrated small populations with just three live specimens found at two sites. This is up from 2006, when no specimens were found across nine sites, though worth mentioning that there was again variance in site sampling due to landowners not giving permission and the addition of new sites in 2019 (McCann and Feller 2020).

At sites where green floaters were found in 2019, there was overall higher mussel abundance and species richness in comparison to sites where green floaters were not found. Though a onetime observation is not a trend, this could be an interesting focus for future research. Threats to existence in these two watersheds are similar to the many broad threats: impoundments, sediment deposition, pollution, and land use changes. Asian clams (Corbicula fluminea) are widespread throughout both watersheds, though not in pointedly high concentrations (McCann and Feller 2020).

Sideling Hill Creek experiences many seasonal changes in hydrology: high flows during storm seasons and snow melts and low flows or no flows during droughts. Changes in hydrology can impact sedimentation and change flow patterns, impacting depth temperature, and more. The report points out that these events are happening more intensively and more frequently due to climate change which may be harmful to green floaters. Another note, was the presence of habitat changes due to beavers. Beavers have impounded at least two green floater sites, potentially leading to their extirpation in these sites. The impact of beavers is inconclusive though as, in two other sites, green floaters were found near recently impounded areas (McCann and Feller 2020). Licking Creek does not have these same seasonal changes, though is still impacted by heavy rains and droughts. Storm events can increase nutrient loads during high flows due to runoff from surrounding livestock and agriculture, reducing water quality, and making green floater habitat unsuitable (McCann and Feller 2020).

As a wide track of land in Sideling Hill Creek is now preserved through The Nature Conservancy as a bioreserve, efforts could be focused on Licking Creek to develop similar protection. Sideling Hill watershed is unique in that even in the face of constant development, the watershed has remained at 80 percent forested. Licking Creek stands at around 40 percent forested, and it is important to preserve the remaining area. Both Sideling Hill Creek and Licking Creek make up parts of the broader Potomac River watershed. In recent years, the Potomac River watershed has has become increasingly developed, though overall it stands at around 50 percent forested. It is important to continue to reduce sediment loads and implement measures to reduce development throughout the watershed.

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Another important note are the several close populations in Pennsylvania just north of the populations in Licking and Sideling Hill Creeks. Similarly, populations in the Potomac River dip into West Virginia and Virginia. Therefore interstate partnerships should be developed to increase populations of green floaters, especially in watersheds that cross state lines (NatureServe 2020).

Figure 2. This map demonstrates the current distribution of the green floater (USFWS SSA 2020).

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THREATS Like other formerly widespread freshwater mussels on the Atlantic Slope, the green floater is vulnerable to extirpation due to a number of threats. Land use changes resulting in increases in urbanization, deforestation, industry, and agriculture are detrimental to the survival of the green floater. Mussels are sensitive to elements and heavy metals such as potassium, nickel zinc, copper, chlorine, and cadmium. Additionally, green floaters, particularly in earlier life stages, can be impacted by toxins, PAHs, PCBs, and other compounds present in runoff of some fungicides, herbicides, insecticides, and ammonia fertilizers, which can lower their siphoning ability or be lethal. Impoundments increase sediment deposition and remove important riparian corridors. Other than occasional passive movement, freshwater mussels are mostly sedentary and cannot move to more favorable habitat (NatureServe, 2020). Habitat degradation is a major issue for mussels, particularly in relation to alteration of flow.

Green floaters and many other mussel species are directly and indirectly by climate change. Increases in water temperatures will reduce their reproductive success as water temperature is a cue for reproduction component in the release of glochidia. Drought can cause die-offs, while severe storm events alter water temperatures, lower dissolved oxygen levels, and suffocate mussels through sedimentation. Changes in precipitation also impact runoff. All of these changes in water quality could also have community wide impacts on ecosystem processes. Other concerns include pathogens, viruses, and other novel diseases (DECNY 2014).

RECOMMENDATIONS FOR FUTURE ACTIONS The main threats to existence for green floater are anthropogenic including: impoundments, sediment deposition, pollution, and land use changes. Recommendations for future actions include mitigating, removing, and preventing these threats; conserving habitat; continuing surveys; and reintroducing the species where possible.

Restoration Implementation Plans Restoration efforts including invasive species removal, stream restoration, and dam removals, while yielding an overall net benefit to the environment, can have unintentional consequences on mussel species such as green floaters. The first step should be determining if the species is present, through either surveying or use of current distributional data. After which, a determination of how the species could be harmed by restoration efforts should be made based on changes in water and sediment flow, frequency, timing, and duration. If green floaters are present and could be negatively impacted, mitigation efforts should be put into place. Where possible, projects could be moved or minimized to reduce harm. Additionally, conducting restoration projects in phases will reduce the duration and impacts of any one event. In situations where this is not possible, mussels could be relocated and salvaged. Throughout projects, there should be constant monitoring to note any signs of distress (Blevins et al. 2019).

Impoundments In the 1900s the increase in damming and channelization of streams and rivers has made much of green floater former habitat uninhabitable. Damming increases silt deposition and lowers oxygen levels upstream, and changes temperature and depth of water downstream. Channelization can have similar impacts, as well as exacerbate flooding events. Disruption of stream connectivity

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can harm reproduction by geographically isolating populations and reducing genetic diversity. Geographic isolation decreases the density of feasible mating populations, lowering the chance of fertilization through siphoning (DECNY 2014). There is some localized documentation of beavers potentially damming some green floater habitat (McCann and Feller 2020).

Where possible remove impoundments. Removing dams and replacing undersized road-stream crossings can dechannelize streams and improve mussel habitat. Removal should be conducted such that existing mussels are not suffocated or stressed. Efforts should also be taken to prevent establishment of future impoundments. If possible, mitigate the impacts of essential impoundments by increasing passage and improving water quality (DECNY 2014).

Sediment Deposition and Pollution Land use changes due to urbanization, deforestation, and agriculture increase erosion and sediment runoff. An increase of sediment loads to stream systems impacts water quality. Sediment loads and changes in water pH corrode shell layers of mussels due to their abrasive and acidic nature. Sediment in the water column can harm feeding mussels by clogging or irritating their gills, leading to suffocation. Both corrosion of shells and excessive silt in gills have been documented as causes of death in mussels. Sediment runoff alters turbidity, light penetration, and water temperature, which effects oxygen levels, impacting green floaters (DECNY 2014).

To reduce the effects of sedimentation on green floaters, conservation practices on agricultural lands to improve water quality should be encouraged. This includes practices such as no-till, cover crops, riparian buffers, diverse crops, crop rotations, and reduction of pesticide applications. For livestock areas, recommendations include installing electric fencing, water troughs, and waste control structures. In urban and suburban areas, homeowners should be encouraged to reduce pesticide use, increase riparian buffer widths, improve stormwater management, and plant cover crops on bare ground. Prevention and enforcement of illegal dumping is also needed (DECNY 2014).

Invasive Species Over 200 nonnative mollusk species have been introduced throughout . Some are invasive and can achieve high densities rapidly over wide geographic stretches. Invasive species, such as the Asian clam or zebra mussel (Dreissena polymorpha) may compete with native mussels such as the green floater by depleting food supplies or dissolved oxygen. Prevention of the introduction of invasive species through best practices such as cleaning and draining boats, trailers, and fishing gear should be encouraged.

Land Use Changes In watersheds where green floaters are present, preserve forested areas, riparian buffers, and wetlands to prevent further residential development. A wide track of land in Sideling Hill Creek is now preserved through The Nature Conservancy as a bioreserve. Similar land protection efforts could be focused on Licking Creek (NatureServe 2020). Where land use changes are necessary, proper storm water management and pervious surfaces should be implemented. Additionally, riparian buffers should be preserved, and vegetation should be prominent throughout to maintain good water quality (DECNY 2014).

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Surveys Resurveying some historic sites would help give a broader understanding to the population decline. Currently, due to resource availability, only multiple sites within the two extant populations are regularly surveyed. Additionally, watersheds with extant populations could be compared to watersheds with extirpated populations to attempt to identify the biggest threats to existence (DECNY 2014). Regular ongoing state-wide population surveys throughout Maryland watersheds to continue assessment of green floater population status are needed. An ideal frequency would be every 2 years. This allows survey efforts to be frequent enough to assess population changes while not disturbing mussels. Additionally, interstate partnerships should be formed to improve understanding of watersheds where green floater are present in Pennsylvania as well (McCann and Feller 2020). Through these surveys, an updated list of high priority populations can be identified for recovery and watershed specific habitat protection and restoration strategies can be developed. Local partners, landowners, and businesses should be educated and informed about the importance of this species and how they can help. These steps would help to make surveying possible in all necessary locations. In 2019, surveyors from Maryland Department of Natural Resources struggled to obtain landowner permission to perform necessary surveys (McCann and Feller 2020).

Reintroduction Reintroduction plans for rare mussel species that have short life spans, such as dwarf wedgemussel ( heterodon) could be relevant to green floaters. In Canada, reintroduction of dwarf wedgemussel was discussed as one possible method for recovery (DOFA 2007). It is possible that the green floater can be reintroduced, based on the guidance and plans for reintroduction of the dwarf wedgemussel. One important caveat is that the green floater has been shown to not rely on a host fish for dispersal and growth. There are two viable techniques. Technique #1 Propagation: Wild adult green floaters are captured and propagated in captivity. Juvenile or adult individuals are then planted in historic habitat ranges. This requires healthy native local populations of mussels that would not be impacted by the removal of specimens. It also requires these populations acclimate to other stream systems and be present in numbers high enough to maintain genetic diversity. Reintroduction must occur in high enough densities for reproduction through the water column to be feasible (DOFA 2007). Additionally, best practices must be used to maintain high genetic diversity within both propagated and wild extant populations. Broodstock size may be a limiting factor in this technique. Technique #2 Transplanting: Wild healthy adult green floaters are captured and relocated to historic habitat ranges. This requires native local populations of mussels to be high enough in population size to not be impacted by translocation in terms of maintaining genetic diversity and reproductive feasibility of the original habitat site. It also requires the ability of the mussel to acclimate from their original site to the reintroduction site. As with propagation, reintroduction must occur in high enough densities for reproduction through the water column to be feasible (DOFA 2007). For many smaller populations in Maryland, this method may not be feasible as transplanting may harm the original site. In their 2014 Species Status Assessment of the green floater, the Department of Environmental Conservation of New York State mentions their efforts to restore degraded habitat and conduct reintroduction efforts through propagation (DECNY 2014). Similarly, the Harrison Lake

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National Fish Hatchery has partnered with the Virginia Department of Game and Inland Fisheries to restore freshwater mussels in Atlantic Slope Rivers through propagation. The hatchery is currently culturing more than 12 different mussel species to reintroduce into rivers. One those species is the green floater.

McMurray and Roe (2017) detail a number of criteria to determine before moving forward with propagation efforts. The first criteria is understanding the causes of the original decline. The second criteria is that mitigation and restoration has occurred to reduce the causes of decline. Both of these criteria lead to the end goal that watersheds are healthy enough so that reintroduction efforts could actually be successful. Other criteria include engaging local, state, and Federal partners, surveying, considering ecological impacts, considering genetic impacts, and setting goals for when the reintroduction efforts will be completed (McMurray and Roe 2017).

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LITERATURE CITED

Blevins, E., McMullen, L., Jepsen, S., Blackburn, M., Code, A., and Black, S. H. (2019). Mussel-Friendly Restoration: A Guide to the Essential Steps for Protecting Freshwater Mussels in Aquatic and Riparian Restoration, Construction, and Land Management Projects and Activities. The Xerces Society for Invertebrate Conservation.

Bogan, A. and M. Ashton. 2016. Manual of the Freshwater Bivalves of Maryland. February 2016. Maryland. 69 pp.

Department of Environmental Conservation of New York State (DECNY). 2014. Species Status Assessment Report for Green floater (Lasmigona subviridis). February 2014. New York. 22 pp.

Department of Fisheries and Oceans (DOFA). 2007. Recovery Strategy for the Dwarf Wedgemussel (Alasmidonta heterodon) in Canada [Proposed]. Species at Risk Act Recovery Strategy Series. Ottowa, Canada 9 pp.

McCann, J. M. and Feller, D. J. 2020. Surveys for Brook Floater (Alasmidonta varicosa) and Green floater (Lasmigona subviridis) in Sideling Hill Creek and Licking Creek, Maryland. Maryland Department of Natural Resources, May 2020. Maryland. 32 pp.

McMurray, Stephen E., and Kevin J. Roe. Perspectives on the controlled propagation, augmentation, and reintroduction of freshwater mussels (: : Unionoida). Freshwater Mollusk Biology and Conservation 20.1 (2017): 1-12.

NatureServe. 2020. NatureServe Explorer: An online encyclopedia of life [web application], Green floater (Lasmigona subviridis), Version 7.1. (http://explorer.natureserve.org). Accessed: 28 April 2020.

Pennsylvania Natural Heritage Program (PNHP). 2012. Freshwater Mussel Species of Concern: Green floater (Lasmigona subviridis), Fact Sheet. 2012. Pennsylvania. 1 pp.

U.S. Geological Survey (USGS). 2019. Nonindigenous Aquatic Species Database, Green floater (Lasmigona subviridis), https://nas.er.usgs.gov/queries/FactSheet.aspx?SpeciesID=146, November 2019. Accessed 1 May 2020.

U.S. Fish and Wildlife Service (USFWS). 2020. Species Status Assessment (SSA) Green Floater (Lasmigona subviridis) DRAFT

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