Benthic Suspension Feeders in Shallow Coastal Water
13
position (e. g., Asmus 1987). These beds can persist for many years (Dankers
and Koelemaij 1989) as complex communities of several year classes of
mussels and their associated fauna (Asmus 1987). Their stability decreases
when large amounts of biodeposits accumulate, causing the mussel beds to
rise high above the surrounding tidal flat and making them vulnerable to
storms and ice scouring. Suffocation from excessive biodeposition and
predation (especially by humans, i. e., fishing) can be a significant mortality
factor as well. A comprehensive description of these processes is given in Seed
and Suchanek (1992).
Probably the most extensive bivalve structures are reefs built by oysters.
For example, the American oyster, Crassostrea virginica, forms reefs that can
be thousands of meters in length and several meters high (Fig. 1.1, see p. 16).
In addition, these reefs may grow large enough to form dams (Fig. 1.1) that
influence the hydrography of marsh creeks (Dame 1996). Like mussel beds,
oyster reefs provide microhabitats for many motile and sessile species. The
number of macro faunal species found on intertidal reefs ranges from 37 (only
macroinvertebrates, Dame 1979) to 303 (Wells 1961).
A few infaunal species may surreptitiously play similar roles. For example,
estimates of the abundance of the cockle Cerastoderma edule (Table 1.1) show
maximum abundance values up to 2000 m- 2 , and maximum biomass levels up
to 400 g dry wt m- 2 (Verwey 1952). However, cockle beds cannot be characterized as communities with a distinct faunal composition (Dankers 1993).
Recently, Gutierrez and Iribarne (1999) described the role of stout razor clams
(Tagelus plebeius) in structuring benthic communities as a result of burrows
and shell matrix accumulations.
Several factors affect biodiversity on bivalve reefs and beds. Studies have
shown that the diversity of species increases with increasing patch size and
with age of the mussel bed. Tidal exposure and mussel density may also be
significant factors causing spatial variation in the associated fauna of the
mussel bed (see Dame 1996 for review). Dame (1996) argued that it is important to recognize the interaction between the physical environment and
the system structure in order to understand the temporal and spatial
development of bivalve communities and their associated fauna.
A number of benthic suspension-feeding bivalve species are dominant
grazers in shallow coastal areas and they can exert a strong control on particle
concentrations in the water column. Based on estimates of the amount of
suspended particulate matter processed by Cerastoderma edule and Mytilus
edulis in the Dutch Wadden Sea, Verwey (1952) concluded that the bivalves
play an important role in the sedimentation processes in this system. Studies
of other systems also indicated that sedimentation of material might be
significantly enhanced by bivalve filtration activity (Haven and MoralesAlamo 1966, 1972). In later studies, it was realized that bivalve filtration can
have an impact on phytoplankton biomass. Data supporting this idea came
13
position (e. g., Asmus 1987). These beds can persist for many years (Dankers
and Koelemaij 1989) as complex communities of several year classes of
mussels and their associated fauna (Asmus 1987). Their stability decreases
when large amounts of biodeposits accumulate, causing the mussel beds to
rise high above the surrounding tidal flat and making them vulnerable to
storms and ice scouring. Suffocation from excessive biodeposition and
predation (especially by humans, i. e., fishing) can be a significant mortality
factor as well. A comprehensive description of these processes is given in Seed
and Suchanek (1992).
Probably the most extensive bivalve structures are reefs built by oysters.
For example, the American oyster, Crassostrea virginica, forms reefs that can
be thousands of meters in length and several meters high (Fig. 1.1, see p. 16).
In addition, these reefs may grow large enough to form dams (Fig. 1.1) that
influence the hydrography of marsh creeks (Dame 1996). Like mussel beds,
oyster reefs provide microhabitats for many motile and sessile species. The
number of macro faunal species found on intertidal reefs ranges from 37 (only
macroinvertebrates, Dame 1979) to 303 (Wells 1961).
A few infaunal species may surreptitiously play similar roles. For example,
estimates of the abundance of the cockle Cerastoderma edule (Table 1.1) show
maximum abundance values up to 2000 m- 2 , and maximum biomass levels up
to 400 g dry wt m- 2 (Verwey 1952). However, cockle beds cannot be characterized as communities with a distinct faunal composition (Dankers 1993).
Recently, Gutierrez and Iribarne (1999) described the role of stout razor clams
(Tagelus plebeius) in structuring benthic communities as a result of burrows
and shell matrix accumulations.
Several factors affect biodiversity on bivalve reefs and beds. Studies have
shown that the diversity of species increases with increasing patch size and
with age of the mussel bed. Tidal exposure and mussel density may also be
significant factors causing spatial variation in the associated fauna of the
mussel bed (see Dame 1996 for review). Dame (1996) argued that it is important to recognize the interaction between the physical environment and
the system structure in order to understand the temporal and spatial
development of bivalve communities and their associated fauna.
A number of benthic suspension-feeding bivalve species are dominant
grazers in shallow coastal areas and they can exert a strong control on particle
concentrations in the water column. Based on estimates of the amount of
suspended particulate matter processed by Cerastoderma edule and Mytilus
edulis in the Dutch Wadden Sea, Verwey (1952) concluded that the bivalves
play an important role in the sedimentation processes in this system. Studies
of other systems also indicated that sedimentation of material might be
significantly enhanced by bivalve filtration activity (Haven and MoralesAlamo 1966, 1972). In later studies, it was realized that bivalve filtration can
have an impact on phytoplankton biomass. Data supporting this idea came