Chapter 15 Key Concepts

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.