Freshwater mussel records collected by the Maryland Department of ...

INTRODUCTION
The diversity of freshwater mussels (Family: Unionidae) in North America is
unmatched globally (Bogan 2008). They are also among the most imperiled fauna with
nearly 70% of species listed as endangered, threatened, or of concern (Williams et al.
1993). Furthermore, extinction rates of freshwater mussels currently exceed rates
observed in terrestrial environments (Allen and Flecker 1993, Ricciardi and Rasmussen
1999). The high rate of imperilment and extinction for mussels has been linked to habitat
and flow alteration, invasive species, loss of host fish, increased siltation, and dam
construction (Ricciardi et al. 1998, Brim Box and Mossa 1999, Strayer 1999a, Vaughn
and Taylor 1999, Watters 2000). Poor land use practices, point and non-point source
pollution have further disrupted freshwater ecosystems ultimately leading to the decline
of mussels throughout North America (Bogan 1993). Currently, 16 native species of
mussels are extant in Maryland (Turgeon et al. 1998), of which five are globally
imperiled or rare (Williams et al. 1993). At the state level, 14 species are listed as being
of Greatest Conservation Need (GCN), of which five are also considered state
endangered (MDNR 2007). Alasmidonta heterodon Lea 1829 is a federally endangered
species, while A. varicosa Lamark 1819 and Lasmigona subviridis Conrad 1835 are being
as considered candidates for federal listing.
Freshwater mussels are long-lived, sessile, suspension feeding bivalves that
provide essential ecological services in aquatic environments (Vaughn and Hakenkamp
2001, Strayer et al. 2004). These services include storage and transfer of nutrients from
the water column to substrate, biodeposition of organic material, nutrient mineralization,
habitat modification and engineering, and stimulating multi-level trophic production
(Nichols and Garling 2000, Raikow and Hamilton 2001, Gutierrez et al. 2003, Vaughn et
al. 2004, Spooner and Vaughn 2006, Vaughn et al. 2007, Vaughn et al. 2008). Mussel
biomass historically dominated rivers of eastern North America, and often exceeds that of
other benthic macroinvertebrates in streams, even though densities of macroinvertebrate
families are higher in habitat containing mussels than where mussels are absent
(Parmalee and Bogan 1998, Howard and Cuffey 2006, Vaughn and Spooner 2006).
Living mussels and their spent valves also provide stabile habitat and nutrients for
periphyton, vascular plants, and other benthic organisms (Beckett et al. 1996, Spooner
and Vaughn 2006, Vaughn et al. 2008). The decline of mussel fauna throughout North
America has likely had major implications for the management, conservation, and
restoration of aquatic species, communities, and functioning stream ecosystems.
The Maryland Department of Natural Resources’ Monitoring and Non-tidal
Assessment Division (MANTA) collects chemical, physical, and biological data to assess
the health of Maryland’s 1 st -4 th order wadeable streams through the Maryland Biological
Stream Survey (MBSS) (Stranko et al. 2007). The MBSS includes data from thousands
of sites that span Maryland’s five physiographic provinces, which is ideal for examining
patterns in faunal distribution across the State. Additional surveys conducted by
MANTA collected similar environmental data from areas not typically sampled by the
MBSS. This spatially intensive survey has already discovered previously unknown
mussel populations and helped refine the extent of species distributions. When these data
includes records of freshwater mussel encounters (i.e. presence), environmental
conditions and their effect upon mussel distribution can be examined. With some
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