Benthic Suspension Feeders in Shallow Coastal Water
25
In barnacles that are feeding passively, increased flow positively influences
growth and recruitment (Sanford et al. 1994) and the building of hummocks
or mounds further accentuates water flow and growth of those animals at the
top of the structure (Pullen and LaBarbera 1991; Bertness et al. 1998).
Hily (1991) published one of the first studies on a community of several
suspension feeders influencing the water quality of the Bay of Brest, located
on the northwest coast of France. The bay is a well-mixed estuarine environment that covers about 10,280 ha with an average depth of 10 m and has a
water volume residence time of 15 to 30 days. The bottom of the bay is
composed of mainly muddy and sandy substrates dominated by eleven suspension-feeding invertebrates. The main sources of suspended particles are
phytoplankton and decomposing macrophytes. The barnacle Balanus crenatus was the dominant suspension feeder in muddy areas, the snail Crepidula
fornicata was most important on slopes and channels, and the echinoderm
Ophiothrix fragilis dominated the gravelly bottoms of the central bay. Suspension feeders were calculated to filter the volume of the bay in 4 to 6 days
or in about 1/3 of the hydrodynamic residence time and equivalent to the
doubling time of the phytoplankton (Fig. 1.3). At this rate of suspension
feeding, these animals can control the density of the phytoplankton and
influence primary production within the bay through the feedback of
inorganic nutrients. These activities, as well as the removal of suspended
detrital particles from the water column, act as a retention mechanism that
further enriches the bay. Thus, the suspension feeders as a functional group
are playing a major functional role in their ecosystem.
In a similar effort, Lemmens et al. (1996) determined the filtering capacities
of the various habitats in Cockburn Sound, Western Australia. By filtration
capacity, these authors mean how much water a given habitat filters per m 2
per day. This is a static comparison of the suspension feeders because they are
assumed to interact with the same amount of water. However, Cockburn
Sound is a coastal system subject to tides, waves, and currents that result in
both vertical and horizontal water fluxes. Thus, without water volume
residence time estimates, it is difficult to determine the net influences of the
suspension feeders on suspended particles or the ecosystem. The authors
argue that because of low suspension-feeder densities in unvegetated and
Heterozostera habitats, filter feeder control of these systems is unlikely. But, in
habitats dominated by the structure-building polychaete Sabella spallanzanii,
filtration capacity may be sufficient to influence suspended particle concentrations. If this is the case, then S. spallanzanii may be a key player in its
ecosystem.
25
In barnacles that are feeding passively, increased flow positively influences
growth and recruitment (Sanford et al. 1994) and the building of hummocks
or mounds further accentuates water flow and growth of those animals at the
top of the structure (Pullen and LaBarbera 1991; Bertness et al. 1998).
Hily (1991) published one of the first studies on a community of several
suspension feeders influencing the water quality of the Bay of Brest, located
on the northwest coast of France. The bay is a well-mixed estuarine environment that covers about 10,280 ha with an average depth of 10 m and has a
water volume residence time of 15 to 30 days. The bottom of the bay is
composed of mainly muddy and sandy substrates dominated by eleven suspension-feeding invertebrates. The main sources of suspended particles are
phytoplankton and decomposing macrophytes. The barnacle Balanus crenatus was the dominant suspension feeder in muddy areas, the snail Crepidula
fornicata was most important on slopes and channels, and the echinoderm
Ophiothrix fragilis dominated the gravelly bottoms of the central bay. Suspension feeders were calculated to filter the volume of the bay in 4 to 6 days
or in about 1/3 of the hydrodynamic residence time and equivalent to the
doubling time of the phytoplankton (Fig. 1.3). At this rate of suspension
feeding, these animals can control the density of the phytoplankton and
influence primary production within the bay through the feedback of
inorganic nutrients. These activities, as well as the removal of suspended
detrital particles from the water column, act as a retention mechanism that
further enriches the bay. Thus, the suspension feeders as a functional group
are playing a major functional role in their ecosystem.
In a similar effort, Lemmens et al. (1996) determined the filtering capacities
of the various habitats in Cockburn Sound, Western Australia. By filtration
capacity, these authors mean how much water a given habitat filters per m 2
per day. This is a static comparison of the suspension feeders because they are
assumed to interact with the same amount of water. However, Cockburn
Sound is a coastal system subject to tides, waves, and currents that result in
both vertical and horizontal water fluxes. Thus, without water volume
residence time estimates, it is difficult to determine the net influences of the
suspension feeders on suspended particles or the ecosystem. The authors
argue that because of low suspension-feeder densities in unvegetated and
Heterozostera habitats, filter feeder control of these systems is unlikely. But, in
habitats dominated by the structure-building polychaete Sabella spallanzanii,
filtration capacity may be sufficient to influence suspended particle concentrations. If this is the case, then S. spallanzanii may be a key player in its
ecosystem.