BIVALVE MOLLUSCS
Loren D. Coen
1 and Raymond E. Grizzle
2
1
Department of Biological Sciences and Harbor Branch
Oceanographic Institute, Florida Atlantic University,
Fort Pierce, FL, USA
2
Department of Biological Sciences and Jackson
Estuarine Laboratory, University of New Hampshire,
Durham, NH, USA
Synonyms
Molluscs; Pelecypods
Definition
Bivalves (nearly 20,000 species) are one class in the
phylum Mollusca (Abbott, 1974; Gosling, 2003; Gofas,
2013). They secrete a relatively hard shell that covers the
mantle and gill tissues. The shell grows out from the point
of articulation, the hinge, with new layers regularly added
from the mantle tissues. Some species live free, singly
(clams), or in dense aggregations (scallops); others live
attached to each other by either byssal threads (Wilker,
2011) or cement (Burkett et al., 2010; Moeller and
Matyjaszewski, 2012). Many serve as economically
important wild stock fisheries or aquaculture species (see
Gosling, 1992, 2003; Spencer, 2002; Hardy, 2006;
Shumway and Parsons, 2006; FAO, 2009, see also FAO
and NMFS websites). Most are filter feeders (Dame,
1993, 1996; Wildish and Kristmanson, 1997) or deposit
feeders (Rhoads, 1973; Kamermans, 1994), but some species are very specialized (Abbott, 1974), boring into
wood, rocks, corals, and even other bivalve species
(Families Teredinidae, Pholadidae, some Mytilidae, and
Veneridae). Clams and mussels (Mytilus, Gosling, 1992),
for example, are found from full strength salinities, in
estuaries to freshwater (perhaps a third of all bivalve species, see Haag, 2012) (Dame, 1996; Levinton, 2013).
Many freshwater clams and mussels reside in isolated
water bodies, have atypical larval adaptations, and are currently endangered (Haag, 2012).
Characteristics
Estuaries and their component habitats are generally
recognized as some of the most productive and important
ecosystems, as they provide critical feeding, spawning,
and nursery areas for numerous species, including economically important fish, shellfish, and waterfowl, in
addition to ecologically valuable invertebrate and vertebrate species (Boesch and Turner, 1984; Beck et al.,
2001, 2003; Barbier et al., 2011). They are also one of
the most impacted ecosystems on the planet (Lotze et al.,
2006; Airoldi and Beck, 2007; Molnar et al., 2008; Beck
et al., 2009, 2011). One important and common species
lineage is the bivalve molluscs, found both intertidally
and subtidally in estuaries. Habitat-forming bivalve
species (ASMFC, 2007) might be viewed as those that
are (1) “reef-forming” (see DeAlteris, 1988; Waldbusser
et al., 2013, Figure 1), (2) “aggregation-forming,” or
(3) “shell-accumulating.” Many species are or were
important economically, including clams, scallops, mussels, and oysters (MacKenzie, 1996, 1997a, 1997b,
1997c; Bell et al., 2005). For example, the softshell clam
(Mya arenaria) once supported a commercial fishery in
the Chesapeake Bay that is currently nonexistent
(Abraham and Dillon 1986). Restocking or restoring these
invertebrates can be very different from conventional finfish approaches (Breitburg et al., 2000; French McCay
et al., 2003; Bell et al., 2005; Arnold, 2008; Beck et al.,
2009; Coen et al., 2011a).
Many “free-living” (e.g., non-reef-forming or
solitary) species occur in coarse sand to “shelly” habitats
cobbles or in submerged aquatic vegetation (SAV)
which can provide some protection from predators
(Sponaugle and Lawton, 1990; Irlandi, 1994; Kraeuter
and Castagna, 2001; Grabowski, 2004; Grabowski
et al., 2008). Many clam species (e.g., hard clams,
Mercenaria spp., softshell clams Mya, etc.) that occur
infaunally are able to “migrate” horizontally, as well as
vertically, when conditions are adverse (Newell and
Hidu, 1986; Dame, 1996) such as low dissolved oxygen
(Diaz and Rosenberg, 1995; Burnett, 1997), whereas
cemented species are unable to relocate (Lenihan and
Peterson, 1998; Lenihan et al., 1999; Altieri and Witman,
2006; Breitburg et al., 2009; Johnson et al., 2009). Loss
of dense populations of bivalves can have significant
ecosystem effects (Altieri and Witman, 2006; Beck et
al. 2011).
Harvesting (¼disturbance) of bivalves and associated
faunas in sediment or reefs (Hall et al., 1990; Coen,
1995; Dayton et al., 1995; Thrush et al., 1995; Lenihan
and Micheli, 2000; Stokesbury et al., 2011) can have significant effects on their functioning and recovery (Hall,
1994; Coen and Luckenbach, 2000; Jackson et al., 2001;
French McCay et al., 2003; Lotze et al., 2006; Grabowski
and Peterson, 2007; Grabowski et al. 2012).
Mobile infaunal species are found in a variety of substrates including sand, mud, shell, and mixtures of these
(Dame, 1996; Levinton, 2013). For example, razor clams
(family Pharidae) can move very rapidly in estuarine sediments with a specialized shell and foot. Non-cementing
scallop species are relatively mobile as juveniles and
adults moving off the bottom for short excursions (Fay
et al., 1983; Shumway and Parson, 2006), for example,
to flee predators (Pohle et al., 1991; Ambrose and Irlandi,
1992; Arnold, 2009). Some species have siphons that are
used for feeding and respiration. These straw-like structures also allow many species to reside deeper in the sediment (soft clams, Mya arenaria; see Figure 2) providing
some protection from both lethal and sublethal predators
(Irlandi, 1994). However, these fleshy tissues are then
available to “sublethal” predators whose diets can be
BIVALVE MOLLUSCS
89
Loren D. Coen
1 and Raymond E. Grizzle
2
1
Department of Biological Sciences and Harbor Branch
Oceanographic Institute, Florida Atlantic University,
Fort Pierce, FL, USA
2
Department of Biological Sciences and Jackson
Estuarine Laboratory, University of New Hampshire,
Durham, NH, USA
Synonyms
Molluscs; Pelecypods
Definition
Bivalves (nearly 20,000 species) are one class in the
phylum Mollusca (Abbott, 1974; Gosling, 2003; Gofas,
2013). They secrete a relatively hard shell that covers the
mantle and gill tissues. The shell grows out from the point
of articulation, the hinge, with new layers regularly added
from the mantle tissues. Some species live free, singly
(clams), or in dense aggregations (scallops); others live
attached to each other by either byssal threads (Wilker,
2011) or cement (Burkett et al., 2010; Moeller and
Matyjaszewski, 2012). Many serve as economically
important wild stock fisheries or aquaculture species (see
Gosling, 1992, 2003; Spencer, 2002; Hardy, 2006;
Shumway and Parsons, 2006; FAO, 2009, see also FAO
and NMFS websites). Most are filter feeders (Dame,
1993, 1996; Wildish and Kristmanson, 1997) or deposit
feeders (Rhoads, 1973; Kamermans, 1994), but some species are very specialized (Abbott, 1974), boring into
wood, rocks, corals, and even other bivalve species
(Families Teredinidae, Pholadidae, some Mytilidae, and
Veneridae). Clams and mussels (Mytilus, Gosling, 1992),
for example, are found from full strength salinities, in
estuaries to freshwater (perhaps a third of all bivalve species, see Haag, 2012) (Dame, 1996; Levinton, 2013).
Many freshwater clams and mussels reside in isolated
water bodies, have atypical larval adaptations, and are currently endangered (Haag, 2012).
Characteristics
Estuaries and their component habitats are generally
recognized as some of the most productive and important
ecosystems, as they provide critical feeding, spawning,
and nursery areas for numerous species, including economically important fish, shellfish, and waterfowl, in
addition to ecologically valuable invertebrate and vertebrate species (Boesch and Turner, 1984; Beck et al.,
2001, 2003; Barbier et al., 2011). They are also one of
the most impacted ecosystems on the planet (Lotze et al.,
2006; Airoldi and Beck, 2007; Molnar et al., 2008; Beck
et al., 2009, 2011). One important and common species
lineage is the bivalve molluscs, found both intertidally
and subtidally in estuaries. Habitat-forming bivalve
species (ASMFC, 2007) might be viewed as those that
are (1) “reef-forming” (see DeAlteris, 1988; Waldbusser
et al., 2013, Figure 1), (2) “aggregation-forming,” or
(3) “shell-accumulating.” Many species are or were
important economically, including clams, scallops, mussels, and oysters (MacKenzie, 1996, 1997a, 1997b,
1997c; Bell et al., 2005). For example, the softshell clam
(Mya arenaria) once supported a commercial fishery in
the Chesapeake Bay that is currently nonexistent
(Abraham and Dillon 1986). Restocking or restoring these
invertebrates can be very different from conventional finfish approaches (Breitburg et al., 2000; French McCay
et al., 2003; Bell et al., 2005; Arnold, 2008; Beck et al.,
2009; Coen et al., 2011a).
Many “free-living” (e.g., non-reef-forming or
solitary) species occur in coarse sand to “shelly” habitats
cobbles or in submerged aquatic vegetation (SAV)
which can provide some protection from predators
(Sponaugle and Lawton, 1990; Irlandi, 1994; Kraeuter
and Castagna, 2001; Grabowski, 2004; Grabowski
et al., 2008). Many clam species (e.g., hard clams,
Mercenaria spp., softshell clams Mya, etc.) that occur
infaunally are able to “migrate” horizontally, as well as
vertically, when conditions are adverse (Newell and
Hidu, 1986; Dame, 1996) such as low dissolved oxygen
(Diaz and Rosenberg, 1995; Burnett, 1997), whereas
cemented species are unable to relocate (Lenihan and
Peterson, 1998; Lenihan et al., 1999; Altieri and Witman,
2006; Breitburg et al., 2009; Johnson et al., 2009). Loss
of dense populations of bivalves can have significant
ecosystem effects (Altieri and Witman, 2006; Beck et
al. 2011).
Harvesting (¼disturbance) of bivalves and associated
faunas in sediment or reefs (Hall et al., 1990; Coen,
1995; Dayton et al., 1995; Thrush et al., 1995; Lenihan
and Micheli, 2000; Stokesbury et al., 2011) can have significant effects on their functioning and recovery (Hall,
1994; Coen and Luckenbach, 2000; Jackson et al., 2001;
French McCay et al., 2003; Lotze et al., 2006; Grabowski
and Peterson, 2007; Grabowski et al. 2012).
Mobile infaunal species are found in a variety of substrates including sand, mud, shell, and mixtures of these
(Dame, 1996; Levinton, 2013). For example, razor clams
(family Pharidae) can move very rapidly in estuarine sediments with a specialized shell and foot. Non-cementing
scallop species are relatively mobile as juveniles and
adults moving off the bottom for short excursions (Fay
et al., 1983; Shumway and Parson, 2006), for example,
to flee predators (Pohle et al., 1991; Ambrose and Irlandi,
1992; Arnold, 2009). Some species have siphons that are
used for feeding and respiration. These straw-like structures also allow many species to reside deeper in the sediment (soft clams, Mya arenaria; see Figure 2) providing
some protection from both lethal and sublethal predators
(Irlandi, 1994). However, these fleshy tissues are then
available to “sublethal” predators whose diets can be
BIVALVE MOLLUSCS
89