Deep-sea deposit-feeding strategies suggested by environmental and feeding constraints

Abstract

Abstract The principle of lost opportunity from optimal foraging theory, coupled with recent information about fluxes in the deep sea, allows prediction of feeding behaviours potentially specific to deep-sea deposit feeders. One possible strategy, thus far documented only indirectly, is to ‘ squirrel ’ away rich food from the seasonal or episodic pulses that recently have been shown to fuel meiofaunal growth. Echiurans and sipunculids show morphological and faecal handling patterns consonant with this suggestion. Where it is prevalent, this foraging strategy can have profound effects on stratigraphy. Autocoprophagy is another expected behaviour across a wider taxonomic spectrum, but one that is especially difficult to document. The principle of lost opportunity also predicts highly selective ingestion, not necessarily accomplished by the assessment of individual particles but possibly through pit building in areas where fluids move near-bed material. Under many depositions regimes, small but abundant feeding depressions may be the primary sites where deposition occurs. Conversely, digestive utilization of heterogeneous refractory substrates like humic acids seems as unlikely as an effective municipal waste recycling system that starts with mixed garbage. High gut: body volume ratios in deep-sea deposit feeders, rather than representing an adaptation to use this heterogeneous and refractory end of the food spectrum, instead may allow (through greater residence time of ingested material) greater conversion and absorption of the labile fraction of sediments as it becomes scarcer. Intense natural selection for particle selection ability in fact is one possible reason for the prevalence of meiofauna in the deep sea, and for the diminutive size of macrofaunal taxa there. This selective pressure probably imposes a very restrictive bottleneck on the initial developmental stages of deposit feeders.