Learn About Lugworms: Food & feeding

Research study 1

drawings showing differences in sand grain bacterial content in the feces of lugworms Abarenicola vagabunda and A. pacificadrawing of lugworm Abarenicola sp. in feeding postureA lugworm’s food consists of decaying organic matter, protists, small nematode worms, and a few bacteria.  However, considerable differences exist in the extent to which certain food items are eaten by different species.  For example, when Abarenicola vagabunda in the San Juan Island, Washington area eats sand with its complement of bacteria and diatoms it digests most of the bacteria and diatoms.  However, when Abarenicola pacifica eats the same sediments, considerably fewer bacteria and diatoms are digested.  Research done at Friday Harbor Laboratories, Washington indicates that less than 5% of the carbon material ingested is utilised by the worm. 

The worm's burrow, which is often located in anaerobic soils, is ventilated by peristaltic movements of its body.  Water is pumped through the burrow from the tail to head end, and it is this movement that softens the sand in the pocket area around the head.  The worm eats this softened soil by engulfing it with its large, frilly, expansible proboscis.  Defecation is prodigious and occurs on a cycle of 10-30min depending upon season and temperature. Hobson 1967 Biol Bull 133: 343; May 1972 Biol Bull 142: 71; see also Fauchald & Jumars 1979 Oceanogr Mar Biol Ann Rev 17: 193 for a review of feeding in polychaetes. Drawing on Right courtesy Fauchald & Jumars 1979.

NOTE  lit. “without air” G.  Lack of oxygen favours growth of hydrogen sulphide-producing bacteria that imparts a black coloration to the soils and a smell of rotten eggs

Research study 2

photograph of fecal casts of many lugworms in Crescent Beach, British ColumbiaBecause lugworms Abarenicola pacifica often live in anaerobic soils in which hydrogen sulphide-producing bacteria thrive, the irrigating of their burrows and pocket-sands with fresh, oxygen-rich water actually cleanses the soil and improves conditions for survival and growth of other microorganisms.  The soil, already rich in nitrogen and phosphorus, is now oxygenated and rid of potentially toxic hydrogen sulphide gas.  Feeding pauses of 6h or so allow bacterial food components to multiply several time.  Are the worms gardening the soils?  Studies at Friday Harbor Laboratories, Washington suggest that the answer is ‘yes’ and, owing to richer growth of edible microorganisms in the pocket area and low extraction of carbon during digestion, a lugworm’s feces may be actually richer in organics than the surrounding sediments.  Hylleberg 1975 Ophelia 14: 113.

Research study 3

drawing showing tube features of a maldanid worm Axiothella rubrocincta in anaerobic sands of Tomales Bay, CaliforniaIn Tomales Bay, California the maldanid worm Axiothella rubrocincta inhabits 30cm-deep, U-shaped tubes formed from aggregated sand grains and mucus.  The worm combines feeding and burrowing activities to form its tube.  The tail end of the tube terminates in a defecation aperture located at the top of a fecal mound, while the head end terminates just below the sediment surface about 15cm distant (see drawing on Left). A funnel-shaped depression in the sediment marks the location of the feeding aperture of the tube a few cm beneath.  The head end of the tube is drawn out into a softish extension, as shown in the figure, which the author thinks functions to prevent sand from entering the tube when the worm withdraws its head after feeding.  The worm is able to move about in its tube for feeding, and for tube maintenance and cleaning.  Sediments and other matter entering the defecation aperture are pushed out by the worm expanding to the appropriate diameter and moving backwards using its setae to grip the inside of the tube.  drawing of maldanid worm Axiothella rubrocincta feeding on sediments

When feeding, the worm emerges from the sediment into the organics-rich funnel region, extends its mucus-covered proboscis, and draws large quantities of particulate matter into the gut by muscular movements of the proboscis aided by ciliary currents. Gut analyses show that Axiothella’s diet consists of detritus, diatoms, and small invertebrates, such as turbellarians, amphipods, and bivalves.  Kudenov 1978 J Exp Mar Biol Ecol 31:209.

NOTE  an adult tube is about 1cm Outside Diameter amd 0.5cm ID

Research study 4

drawings of feeding parts of maldanid wormsIn a related article the same author compares feeding in Axiothella rubrocincta and 2 other maldanid species Clymenella californica and Praxillella pacifica in Tomales Bay, California.  All 3 species lnhabit tubes and deposit-feed in similar fashion using extensible probosces as shown in the drawings to the Left.  Feeding commences by rapidly protruding and retracting the probosces into and out of the substratum until its dilitancy changes, that is, the sand “puddles”). 

drawing showing feeding in a maldanid worm Praxillella pacificaAs shown in the drawing (on Right) for Praxillella pacifica, as the proboscis everts and inverts into the sediment, and puddles it, papillae on the proboscis work to force particles into the bucco-pharyngeal pocket.  It is at this time that edible particles are sorted from sediment particles and moved by ciliary currents into the esophagus.  Particles selected by large individuals of all 3 species are about 100µm in size. Kudenov 1977 Zool J Linnean Soc 60: 95.

Research study 4.1

photograph of a windmill worm Praxillura maculata Unlike other representatives in the Maldanidae Family that deposit-feed from burrows, the maldanid worm Praxillura maculata constructs a specialised feeding tube out of cemented sand grains. The common name for P. maculata is the Windmill Worm so, while its unusual spoked tube has been documented in the past, it was not until SCUBA-diving researchers from Fisheries & Oceans Canada and University of Washington observed its behaviour in situ (10-20m depth) that its role in feeding was understood. The worm fashions its 2-7cm tube with 6-12 spokes at the top (each 0.5mm diameter and about 25mm in length) and adorns it with a mucus-net web that catches organic particles (see photograph). Although the researchers do not observe actual web construction, they recount seeing one worm extend from its tube, methodically busy itself with its mouth on an already constructed web between the spokes, and then withdraw into the tube while pulling a thread of the mucus net along with it. Thus, the entire web and contents appears to be swallowed en masse. The authors compare the feeding method of Praxillura with those of other worms and other invertebrates, and conclude that no similar feeding method is employed by any other marine animal. McDaniel & Banse 1979 Mar Biol 55: 129. Photograph courtesy the authors.

NOTE other mucus-net eating polychaetes, but not involving an externally constructed web, include parchment worms Chaetopterus spp. These infaunal burrowers construct mucous filtering nets within their tubes, which they eat when they become clogged with particles. For more on chaetopterid feeding go to LEARNABOUT/TUBEWORM/tubeFeed.php#RS2


Tube of windmill worm Praxillura maculata with spokes
festooned with mucus net bearing particulate matter

Research study 5

drawing showing method of collecting feces from a maldanid worm Axiothella rubrocinctaThe maldanid Axiothella rubrocincta is a common deposit-feeding polychaete along the Pacific coast of North America.  It lives on sand-flats in U-shaped burrows that may reach 30cm in depth.  Sand is consumed, processed, and defecated in a mound on the sediment surface.  How much sand does an adult Axiothella produce and what factors influence its rate of sediment processing?  This is determined in an in situ field study in Tomales Bay, California.  The author contains and measures the amount of defecated material over a 24-h period by pressing an open-ended plastic pipe into the sediment around the tail end of the worm.  By inserting filter papers with holes cut into their centres as shown in the diagram, the processed sediments can be retrieved, dried, and weighed. Factors that positively influence the rate of working of the sediments include temperature and salinity, while those that negatively influence rates include organic-carbon content and grain size.  The author concludes that A. rubrocincta is a non-selective deposit-feeder. Kudenov 1982 Mar Biol 70: 181.

Research study 6

photograph of a fat inkeeper worm Urechis caupoA study on DOM (Dissolved Organic Matter) uptake and metabolism in larvae of fat inkeeper worms Urechis caupo by researchers at the University of Southern California shows that radioactively labelled alanine is readily absorbed from solution and catabolised for energy by 4d-old larvae. As such studies can only be done without risk of contamination from resident bacteria present in the larvae, the authors use axenic or bacteria-free cultures. Based on their measured uptake data and metabolic rates of the larvae, and on known concentrations of alanine in the culture vessels, the authors estimate that about 50% of a larva’s metabolic demand could be provided by transport and catabolism of this single amino acid (at 15oC). The study adds Urechis caupo to a growing list of marine-invertebrate larvae that can take up and metabolise DOM. Jaeckle & Manahan 1989 Biol Bull 176: 317. Photograph courtesy Brenna Green, California.

NOTE adult Urechis are handy in this regard, because before their release in each sex the gametes are stored in sacs in the upper part of the coelom. Bacteria-free gametes are obtained by aseptic removal of the sacs in vivo. Most or all studies on DOM uptake in larvae nowadays employ axenic-culture methodologies

Adult fat inkeeper worm at 3m depth
in Monterey Bay, California 0.75X

Research study 7

Researchers at Friday Harbor Laboratories, Washington present a detailed account of functional morphology of guts in west-coast polychaetes, including lugworms Abarenicola pacifica and A. vagabunda.  All 42 species are divided into either carnivores (most having a simple, tubular gut) or depost-feeders (having either single-, 2-, 3-, 4- or 5-compartment guts).  Species with enzymatic digestion incline to simple, tubular guts, while those with digestive fermentation usually have guts characterised by chambers that enable mixing and allow for variable particle-residence times.  For whatever special function they serve, A. pacifica has a 3-compartment gut, while A. vagabunda has a 4-compartment one.  There seems to be no obvious explanation for this, as feeding habits and foods seem to be similar in the 2 species, and it may be something that has potential for future research.  The authors provide much information on gut architecture of each species, including lengths and volumes of parts, and for a few species also consider aspects of ontological scaling.  Penry & Jumars 1990 Oecologia 82: 1.

NOTE  of the 42 species in the study, most are from the west-coast, but about one-third arefrom the Atlantic coast.  Most are shallow-water coastal species, but a few are deep-sea inhabitants

NOTE  in an earlier paper the same authors review functions of animal guts from the standpoint of chemical-reactor theory, with Abarenicola spp., despite the compartmentalised morphology of their guts, being categorized as “plugged-flow reactors".  In such a gut, reactants continuously enter and products continuously exit with no mixing along the flow path.  How a compartmentalised architecture is more effective for this than a simple tubular gut is not discussed by the authors. Penry & Jumars 1987 Am Nat 129 (1): 69.