• Sediment grain size is an important determinant of the distribution of benthos and increases with increasing current strength.
  • Sediment sorting and grain size angularity also reflect the hydrodynamic regime.
  • In very shallow, sandy, wave-swept bottoms, currents generate ripples and bars, which create spatially varying microhabitat variation for benthic organisms.
  • Burrowers live in sediment ranging from packed sand to elastic mud to watery mud.
  • Soft-sediment burrowers use hydromechanical and simple digging mechanisms to move through soft sediment.
  • Interstitial animals adapt to water flow and life in small spaces among particles by means of a simplified body plan, a wormlike shape, or by adhering to particles by means of mucus, suckers, and hooks.
  • Sediments consist of an oxygenated layer overlying an anoxic zone.
  • In sediments in quiet water, there is usually a vertical zonation of microorganisms.
  • Deposit-feeding macrobenthic animals ingest sediment and derive their nutrition mainly from microalgae and particulate organic matter. Free-living sediment bacteria are digestible but not quantitatively important in the diet of larger macrobenthos.
  • Particulate dead organic matter is also important in the nutrition of many deposit feeders.
  • Deposit feeders use a cocktail of enzymes and compounds with surfactant properties to digest organic matter from ingested particulate material.
  • Microbes and particles comprise a complex renewable resource system for deposit feeders.
  • Many benthic animals do not feed directly on microorganisms but have symbiotic chemoautotrophic bacteria, which derive energy from dissolved ions in seawater.
  • Deep feeders cause overturn of the sediment and strongly affect the soft-sediment microzone.
  • Head-down deposit feeders create biogenically graded beds.
  • Hydrodynamic forces at the sediment-water interface cause sediment transport, which often induces switches from deposit feeding to suspension feeding.
  • Deposit feeders can optimize their intake by adjusting food particle size and gut passage time.
  • Passive suspension feeders collect food by means of morphological structures that protrude into the flow and capture particles.
  • Active suspension feeders are under some constraints similar to passive suspension feeders, but they also generate their own water currents to channel and ingest particles.
  • Suspension feeders must be able to avoid clogging from heavy particle loads.
  • Many suspension feeders can select for nutritionally valuable particles and reject poor particles before they enter the gut.
  • Selectivity after particle collection can be studied with a surgical endoscope.
  • Surface properties of algae allow suspension feeders to discriminate among different food sources.
  • Suspension feeders may live in current regimes that deliver particles in uniform currents, but sometimes flow and particle supply direction may be very complex.
  • Carnivory relies on mechanisms of prey search, location, seizure, and ingestion.
  • Benthic herbivores are divided between microalgal and macroalgal-plant feeders.
  • Some benthic herbivores can feed on highly indigestible plant material.
  • Benthic plants have evolved both mechanical and chemical defenses to deter herbivory.
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