Particle capture mechanisms in suspension-feeding invertebrates

Abstract

A large number of suspension-feeding aquatic animals (e.g. bivalves, polychaetes, ascidians, bryozoans, crustaceans, sponges, echinoderms, cnidarians) have specialized in grazing on not only the 2 to 200 µm phytoplankton but frequently also the 0.5 to 2 µm free-living bacteria, or they have specialized in capturing larger prey, e.g. zooplankton organisms. We review the different particle capture mechanisms in order to illustrate the many solutions to the common problem of obtaining nourishment from a dilute suspension of microscopic food particles. Despite the many differences in morphology and living conditions, particle capture mechanisms may be divided into 2 main types. (1) Filtering or sieving (e.g. through mucus nets, stiff cilia, filter setae), which is found in passive suspension feeders that rely on external currents to bring suspended particles to the filter, and in active suspension feeders that themselves produce a feeding flow by a variety of pump systems. Here the inventiveness of nature does not lie in the capture mechanism but in the type of pump system and filter pore-size. (2) A paddle-like flow manipulating system (e.g. cilia, cirri, tentacles, hair-bearing appendages) that acts to redirect an approaching suspended particle, often along with a surrounding 'fluid parcel', to a strategic location for arrest or further transport. Examples include (1) sieving (e.g. by microvilli in sponge choanocytes, mucus nets in polychaetes, acidians, and salps among others), filter setae in crustaceans, 'ciliary sieving' by stiff laterofrontal cilia in bryozoans and phoronids; and (2) 'cirri trapping' in mussels and other bivalves with eu-laterofrontal cirri, ciliary 'catch-up' in bivalve and gastropod veliger larvae, some polychaetes, entroprocts, and cycliophores. These capture mechanisms may involve contact with a particle, and possibly mechanoreception or chemoreception, or may include redirection of particles by the interaction of multiple currents (e.g. in scallops and other bivalves without eu-laterofrontal cirri). Based on the review, we discuss the current physical and biological understanding of the capture process and suggest a number of specific problems related to particle capture, which may be solved in the future using advanced theoretical, computational and experimental techniques.

Trophic relationships between the farmed pearl oyster Pinctada margaritifera and its epibionts revealed by stable isotopes and feeding experiments

“…However, the difference in CR of Didemnum sp., which indicated a higher CR for cyanobacteria than for nanoeukaryotes, is a surprising finding and is difficult to interpret. This result is even more surprising since no specific organ has been described for ascidians that allows for the sorting of particles (Riisgård & Larsen 2010). However, the same result was obtained on 2 different dates.…”

“…The differences of SIR between pearl oysters and ascidians could thus be explained by a differential use of phytoplanktonic food sources, according to particle size. These differences are likely related to differences in sorting abilities between bivalves and ascidians, with bivalves being well known for their ability to sort and select food particles, in contrast to ascidians (Ward & Shumway 2004, Riisgård & Larsen 2010. Even if there is a diet overlap for some food items, the similar growth rate measured for pearl oysters in the presence or absence of epibionts (Lacoste et al 2014b) indicated that biofouling does not prevent pearl oysters from accessing sufficient food resources to support their growth.…”

Metabolism, Consumption Rates, and Scope for Growth of Porcelain Crab (Petrolisthes galathinus)

“…Porcelain crabs, barnacles, calanoid copepods, and most branchiopods use filter setae to capture particles (Riisgard and Larsen, 2010). On the basis of their size and structure, filter setae only capture particles of certain sizes, shapes, and surface chemistry (Palmer et al, 2004), making them more selective than pump systems.…”

“…Oysters, like many bivalves, feed using laterofrontal cirri to create currents, or a pump system, that directs food particles to the mouth (Riisgard and Larsen, 2010). Crassostrea virginica is able to consume suspended particles 1-12 mm in diameter and optimally consumes those between 3 mm and 4 mm (Haven and Morales-Alamo, 1970).…”

“…Suspension feeders remove suspended particles, nutrients, zooplankton, and phytoplankton from the water column and alter current flow; thus, they also alter energy flow and are essential energy links between primary producers and higher trophic levels (Dame and Patten 1981;Powell 1994;Riisgard and Larsen 2010). The porcelain crab Petrolisthes galathinus (Bosc, 1802) is a common suspension feeder found within oyster reef communities in the Gulf of Mexico.…”