360
K. Reise
down shore, and at gentle beach slopes they also perform tidal migrations.
Highest abundance and biomass are found at beaches where upwelling waters
provide an ample food supply.
In most coastal waters the amount of suspended food is a highly variable
commodity and growth phases of suspension feeders are then limited to short
seasons. On the other hand, when phytoplankton is abundant, this is a very
desirable food source, and some surface deposit feeders find an advantage in
switching to suspension feeding (Riisgard and Kamermans, Chap. 4). Various
benthic invertebrates of the shore are capable of gathering food directly from
the water as well as from the sediment surface. Generally, high flow conditions
favour suspension feeding, although there are upper limits, while in calm
waters deposit feeding is more profitable.
Some animals may generate their own currents and thus perform suspension feeding even under otherwise low flow conditions. This is done by the
ragworm Nereis diversicolor, a common polychaete in European estuaries. It
lives in a U-shaped burrow and consumes deposits from the sediment surface
in the immediate surrounding of its burrow openings. In spring and summer,
when phytoplankton concentration is high, the worm remains in the burrow,
moves backward and secretes a fine-meshed mucus net, and then pumps
water through the funnel-shaped net-bag by undulating movements of its
body. After a few minutes the worm moves forward again and swallows the
net together with the retained particles. Using this method, the worms are as
efficient in suspension feeding as mytilid mussels. They may even deplete
their planktonic food source in shallow waters under low flow conditions.
The tellinid clam Macoma balthica is less efficient in suspension feeding. It
has a narrow inhalant siphon and a rather small gill area for filtering. Nevertheless, this common bivalve of the North Atlantic shores may occasionally be
forced to employ suspension feeding. It normally sweeps food particles from
the surrounding sediment surface with its long inhalant siphon, while
otherwise remaining with its body buried well below the surface. The long
siphons are often cropped by fish when the tide is in, and wading birds probe
for the whole animal when the tide is out. Thus, there is a trade-off between
suspension or deposit feeding and exposure to predators. At times it may be
necessary to retract the siphons from the sediment surface when there are too
many encounters with siphon nippers. Also, the remaining length of the
siphon maybe used to stay as deep as possible below the surface, out of reach
to flocks of probing birds. In these situations, M. balthica switches to suspension feeding. The food supply will be rarely sufficient for long. However, for
short periods reduced rations of food may be the preferred evil when predators abound.
Feeding behavior may vary with habitat conditions and individual fates.
M. balthica in the European Wadden Sea mainly feeds when the tide is in. The
related Tellina opalina is abundant on tidal flats in the Indo-Pacific. It uses the
K. Reise
down shore, and at gentle beach slopes they also perform tidal migrations.
Highest abundance and biomass are found at beaches where upwelling waters
provide an ample food supply.
In most coastal waters the amount of suspended food is a highly variable
commodity and growth phases of suspension feeders are then limited to short
seasons. On the other hand, when phytoplankton is abundant, this is a very
desirable food source, and some surface deposit feeders find an advantage in
switching to suspension feeding (Riisgard and Kamermans, Chap. 4). Various
benthic invertebrates of the shore are capable of gathering food directly from
the water as well as from the sediment surface. Generally, high flow conditions
favour suspension feeding, although there are upper limits, while in calm
waters deposit feeding is more profitable.
Some animals may generate their own currents and thus perform suspension feeding even under otherwise low flow conditions. This is done by the
ragworm Nereis diversicolor, a common polychaete in European estuaries. It
lives in a U-shaped burrow and consumes deposits from the sediment surface
in the immediate surrounding of its burrow openings. In spring and summer,
when phytoplankton concentration is high, the worm remains in the burrow,
moves backward and secretes a fine-meshed mucus net, and then pumps
water through the funnel-shaped net-bag by undulating movements of its
body. After a few minutes the worm moves forward again and swallows the
net together with the retained particles. Using this method, the worms are as
efficient in suspension feeding as mytilid mussels. They may even deplete
their planktonic food source in shallow waters under low flow conditions.
The tellinid clam Macoma balthica is less efficient in suspension feeding. It
has a narrow inhalant siphon and a rather small gill area for filtering. Nevertheless, this common bivalve of the North Atlantic shores may occasionally be
forced to employ suspension feeding. It normally sweeps food particles from
the surrounding sediment surface with its long inhalant siphon, while
otherwise remaining with its body buried well below the surface. The long
siphons are often cropped by fish when the tide is in, and wading birds probe
for the whole animal when the tide is out. Thus, there is a trade-off between
suspension or deposit feeding and exposure to predators. At times it may be
necessary to retract the siphons from the sediment surface when there are too
many encounters with siphon nippers. Also, the remaining length of the
siphon maybe used to stay as deep as possible below the surface, out of reach
to flocks of probing birds. In these situations, M. balthica switches to suspension feeding. The food supply will be rarely sufficient for long. However, for
short periods reduced rations of food may be the preferred evil when predators abound.
Feeding behavior may vary with habitat conditions and individual fates.
M. balthica in the European Wadden Sea mainly feeds when the tide is in. The
related Tellina opalina is abundant on tidal flats in the Indo-Pacific. It uses the