Benthic Suspension Feeders in Shallow Coastal Water
29
maximum biomass than less active species (Herman et al. 1999). Food
depletion in the water column is reduced by a high bottom roughness because
this roughness generates turbulence that increases vertical mixing over
potential suspension feeders. Bivalves can enhance turbulence by building
rough and tall reefs and by producing outflow 'jets' as a by-product of their
pumping (O'Riordan et al. 1995). In addition, the occurrence of animals in
patches further increases the roughness (Frechette et al. 1989; Herman et al.
1999). Bed roughness and the concurrently generated turbulence are enhanced by the morphology of the animal's shells and the topography generated by the dense packing of suspension feeders. In barnacles and mussels,
the development of hummocks increases flow, benefits individual animal
growth at the top of the hummocks and traps particles in the troughs between
peaks (Seed and Suchanek 1992; Bertness et al. 1998; Thomason et al. 1998).
Oysters and their reefs also develop structural attributes that increase elevation over the substrate and flow over the reef. These developments are also
the product of individual shell structure, i. e., elongated growth forms in C.
virginica, and increased reef height above the substrate (Bahr and Lanier
1981).
In a review of the evolution of all types of reefs, Wood (1999) argues that
reefs made up of aclonal organisms, e. g., oysters, etc., are primitive because
these systems are of low relief, relatively short duration and low community
diversity. In contrast, clonal reefs, e. g., corals, are of high relief, long duration
and high community diversity. She further contends that most aclonal
systems are dominated by organisms that utilize the turbid shallow waters
with their variable salinities and elevations as refuges from marine predators.
In order to utilize these shallow environments, benthic suspension feeders
usually exhibit synchronous spawning, gregarious settlement and rapid early
growth in order to compete successfully against clonal forms for the limited
hard surfaces in these soft -sediment environments.
Thus, suspension-feeding benthos from shallow water and intertidal
environments need rapid and plastic growth, synchronized reproduction and
gregarious recruitment because they live in a dynamic and unpredictable
environment. These characteristics also enable them to control their major
food source, the phytoplankton. The dominant benthic suspension feeder in
each system in the lower portion of Fig. 1.3, oysters, mussels, clams, and
ascidians, as well as the combination of species in the Bay of Brest, exhibit
most of these characteristics. These suspension feeders have sufficient filtration capacity (density x filtration rate) to have a shorter system clearance
time than water volume residence time which allows them to potentially control phytoplankton.
In the last century, there have been well-recorded and dramatic changes to
the suspension-feeding benthos in Chesapeake Bay, Delaware Bay, San Francisco Bay, Marennes-Oleron and the Wadden Sea (Dame 1996 for a review). In
29
maximum biomass than less active species (Herman et al. 1999). Food
depletion in the water column is reduced by a high bottom roughness because
this roughness generates turbulence that increases vertical mixing over
potential suspension feeders. Bivalves can enhance turbulence by building
rough and tall reefs and by producing outflow 'jets' as a by-product of their
pumping (O'Riordan et al. 1995). In addition, the occurrence of animals in
patches further increases the roughness (Frechette et al. 1989; Herman et al.
1999). Bed roughness and the concurrently generated turbulence are enhanced by the morphology of the animal's shells and the topography generated by the dense packing of suspension feeders. In barnacles and mussels,
the development of hummocks increases flow, benefits individual animal
growth at the top of the hummocks and traps particles in the troughs between
peaks (Seed and Suchanek 1992; Bertness et al. 1998; Thomason et al. 1998).
Oysters and their reefs also develop structural attributes that increase elevation over the substrate and flow over the reef. These developments are also
the product of individual shell structure, i. e., elongated growth forms in C.
virginica, and increased reef height above the substrate (Bahr and Lanier
1981).
In a review of the evolution of all types of reefs, Wood (1999) argues that
reefs made up of aclonal organisms, e. g., oysters, etc., are primitive because
these systems are of low relief, relatively short duration and low community
diversity. In contrast, clonal reefs, e. g., corals, are of high relief, long duration
and high community diversity. She further contends that most aclonal
systems are dominated by organisms that utilize the turbid shallow waters
with their variable salinities and elevations as refuges from marine predators.
In order to utilize these shallow environments, benthic suspension feeders
usually exhibit synchronous spawning, gregarious settlement and rapid early
growth in order to compete successfully against clonal forms for the limited
hard surfaces in these soft -sediment environments.
Thus, suspension-feeding benthos from shallow water and intertidal
environments need rapid and plastic growth, synchronized reproduction and
gregarious recruitment because they live in a dynamic and unpredictable
environment. These characteristics also enable them to control their major
food source, the phytoplankton. The dominant benthic suspension feeder in
each system in the lower portion of Fig. 1.3, oysters, mussels, clams, and
ascidians, as well as the combination of species in the Bay of Brest, exhibit
most of these characteristics. These suspension feeders have sufficient filtration capacity (density x filtration rate) to have a shorter system clearance
time than water volume residence time which allows them to potentially control phytoplankton.
In the last century, there have been well-recorded and dramatic changes to
the suspension-feeding benthos in Chesapeake Bay, Delaware Bay, San Francisco Bay, Marennes-Oleron and the Wadden Sea (Dame 1996 for a review). In