Optimal foraging by deposit-feeding invertebrates: Roles of particle size and organic coating

Abstract

Feeding experiments were conducted on marine, deposit-feeding benthic invertebrates to test the predictions of an optimal foraging model. Food item selection based on sediment particle size and presence or absence of an organic coating on particles was investigated. Animals displaying a wide range of feeding mechanisms were studied in particle size-selection experiments using artificial sediment of closely controlled size composition. Nine of 10 species from 4 phyla ingested smaller particles in greater proportions than the particles were present in the sediment. In experiments where animals fed on a mixture of two particle types, one with and one without a surface protein coating, 6 of 7 species from 3 phyla ingested preferentially the protein-coated beads. While these trends of selection of smaller particles and protein-coated particles follow qualitatively the predictions of the optimal foraging model, the animals did not ingest exclusively the preferred particle types. Mechanics of particle handling rather than behavioral responses to particle characteristics appear to offer the better explanation for the observed selection patterns. In particular, the results support strongly the recently proposed role of mucous adhesion in particle selection by deposit feeders.These and other results from studies of deposit feeders suggest that factors in addition to food item selection must be considered when testing the assumptions and predictions of optimal foraging theory. Specifically, feeding energetics are also affected by postfood-selection processes such as variation of ingestion rate. Furthermore, the effects of abiotic environmental factors on foraging behavior cannot be overlooked in evaluating the optimality of foraging behavior; variable water velocity affected differently the particle size selectivity of 3 sympatric polychaete species in these studies.

Measurement of Bioturbation Rate in Tube-Building Maldanid Worms (Polychaeta: Maldanidae) with a Video Observation System

“…Taghon & Jumars (1984) reported that, for three deposit-feeding polychaetes, Amphicteis scaphobranchiata, Hobsonia florida, and Pseudopolydora hempi japonica, ingestion rates varied with nutritional conditions in artificial sediments, and they suggested that the increasing ingestion rate with nutrition supported the prediction of the model of Taghon (1981Taghon ( , 1982. This hypothesis suggests that body size should be related to foraging and ingestion strategy in deposit feeders (Penry & Jumars 1987).…”

“…Feeding rates of deposit feeders have been studied in terms of organic matter/energy intake (Yingst 1976) and optimal foraging (Doyle 1979;Taghon 1982). On the other hand, it is well known that benthic infauna sometimes have enormous effects on sediment structure by reworking the sediment through such activities as feeding, defecation, burrowing, tube-building, irrigation, and ventilation (Lopez & Levinton 1987) .…”

Eelgrass habitat near Liberty Bay: Chapter 5

“…At that depth, burrowing of benthic organisms, including Macoma spp., may cause changes in the environment that cause gradients in interstitial N compounds due to the nitrification and denitrification at various depths (Grundmanis and Murray, 1977). In addition to changing its surrounding environment, experiments with Macoma balthica in Puget Sound indicated it fed selectively on surface sediment particles selecting for protein-coated particles (Taghon, 1982). This selective feeding might result in δ 15 N enrichment if the surface phytobenthos and bacteria contributed significantly to the diet.…”

“…This small difference is attributed to the terrigenous sediment POM that likely is more abundant in Liberty Bay sediments. The terrigenous low-density particles high in total organic carbon detected in the sediments of Puget Sound are a potential food source for benthic organisms because of the protein enrichment on the surface of the particles (Taghon, 1982).…”

Experimental evidence of subsurface feeding by the burrowing ophiuroid Amphipholis gracillima (Echinodermata)

“…Particle selection by deposit-feeding organisms has been addressed frequently (e.g. Powell 1977, Jumars et al 1982, Taghon 1982, Self & Jumars 1988. Many organisms preferentially ingest small particles of low specific gravity and large surface areas (Taghon 1982, Self & Jumars 1988.…”