Because food flux to the abyssal plain is limited most echinoderm species will deposit feed, ingesting large quantities of low nutritional value sediment in order to gain a net input of energy (Hudson et al. 2004).However echinoderms have also adapted other feeding methods which are more selective and reduce the need to process much ‘waste’ or non-nutritional material.
Brittle stars are opportunistic omnivores using a combination of scavenging, deposit and suspension feeding methods. Amphiura filiformis is a deep-sea brittle star which shows switching between suspension and deposit feeding depending on current speeds and re-suspension of particulate matter (Rosenberg et al. 1997).
Some suspension feeding brittle stars will also live associated with sessile fauna (e.g. sea pens) which they use as substratum for elevation into benthic currents (Figure 5; Fujita 2001).
Deep-sea Asteroidea will also employ deposit, suspension and scavenging feeding modes to fully utilize limited deep-sea food supply. Mud ingesting species, Hyphalaster inermis, rely on bacterial carbon as a major source of nutrition but also scavenge on large organic food sources switching between feeding methods with relation to food availability (Howell et al. 2003). Predatory species (Dytaster grandis) will plough though the sediment ingesting sediments and the range of infaunal organisms within. Suspension feeding sea stars, such as Freyella elegans, will depend mainly on phytodetrius but will consume live and dead copepods (Howell et al. 2003).
Deep sea echinoids are primarily deposit feeders consuming holothurian fecal casts and meiofauna within the sediment (Lauerman and Kaufmann, 1998). Other omnivorous echinoids feed on phytodetritus or graze on the sediment surface ingesting particulate organic content (Figure 6; Smith and Stockley, 2005).
Holothurians are mainly surface deposit feeders consuming sediment containing diatoms and phytodetritus (Figure 6). Effective digestion of sediment is often determined by the residence time of particles in the digestive tract hence the long and looped structure of the gut found in deep sea holothurians (Hudson et al. 2004). Sea cucumber particle selection is dependant on tentacle morphology, with delicate finger-like tentacles used to ‘rake’ finer particles and stubbier tentacles used to sweep for less selective particle matter (Hudson et al. 2003).
Crinoids are suspension feeders, using and upwards facing mouth into which food is transported by tube feet bearing arms. Tube feet selectively filter small plankton and suspended material from current flow and transport particles entrapped within mucus strings to the organism’s mouth.