Learn About Lugworms: Burrows & bioturbation

Research study 1

drawing of the head end of a lugworm showing how it puddles the sandAbarenicola burrows by extending its proboscis into the sand, moving it back and forth to create a space, then expanding and extending its body into this space.  As the cycle is repeated, drawing of a lugworm showing flanges that act as anchors in the sanddifferential contractions of circular muscles in each body segment create flanges that act as penetration anchors.  These anchors aid in pulling the posterior part of the body into the sand and in extending the proboscis into the sand.  Trueman & Ansell 1969 Oceanogr Mar Biol Ann Rev 7: 315; Wells 1961 p. 209 In The cell and the organism (Ramsay & Wigglesworth, eds.) Cambridge Univ Press.

Research study 2

burrow of a lugworm Aberenicola pacifica
Two burrows in the sands of Cresent Beach, British Columbia, one of a lugworm Abarenicola pacifica; the other, of a ghost shrimp. The tail end of the lugworm burrow is indicated by the characteristic ropy fecal strands 0.3
Densities of lugworms Abarenicola pacifica may reach 1000 or more per square meter and their burrowing activities result in considerable turning-over of surface sediments.  The turned-over sediments are oxidized when exposed to air and hydrogen sulphide-producing bacteria are killed.  For these reasons, mud andsand areas inhabited by lugworms and other bioturbating invertebrates suchas mud- and ghost-shrimps are usually healthier than in areas where they are absent.photograph of lugworm Abarenicola pacificum
Pacific lugworm Abarenicola pacifica

Research study 3

drawing of a lugworm Abarencola pacifica in its burrow
photograph showing several fecal mounds of lugworms Abarenicola pacificaBurrows of lugworms Abarenicola pacifica are readily identifiable by their associated fecal mounds.  The burrow’s shape has been variously described at J-, U-, or L-shaped, depending upon the extent to which the head shaft is filled in with collapsed sand.  A worm of 10cm in length inhabits a burrow about twice that length and about 10cm in depth.  The burrow’s front opening is located within or below a shallow depression caused by the worm engulfing sediments from the head or pocket end, passing them through the digestive tract, and depositing them as a long ropey fecal mound at the tail end.  Although the fecal mound is easily seen, the location of the depression is often obliterated by waves as the tide recedes. Swinbanks & Murray 1981 Sedimentology 28: 201; Taghorn & Green 1990 J Exper Mar Biol Ecol 136: 197; drawings modified from Hylleberg 1975 Ophelia 14: 113.

Research study 4

drawing of worm Pygospio elegansThe volume of turned-over sediments may smother the burrows of other smaller species of worms, for example, spionids.  In False Bay, Washington densities of 2 of these species of spionids Pygospio elegans (drawing on Left) and Pseudopolydora kempi may reach 16,000-60,000 per square meter.   In turn, the burrowing activities of these latter species may smother or drive away juvenile lugworms.  Wilson 1981 J Mar Res 39: 735; Brenchley 1981 J Mar Res 39: 767.

Research study 5

plot showing distribution of lugworm Abarenicola pacifica burrows in False Bay, WashingtonBurrows of lugworms Abarenicola pacifica are neither randomly distributed nor permanent.  Summer assessments in False Bay, Washington show clumped distributions of burrows, and movements by most worms to new locations after 2wk or so.  Other observations are that most worms defecate within 2h of tidal exposure and that worm size correlates poorly with volume of fecal mound, but strongly with diameter of the fecal string.  Kruger & Woodin 1983 Limnol & Oceanogr 38: 509.

The dots show a clumping distribution of lugworms A. pacifica in a 0.25sq m
plot in False Bay, Washington. There are 127 worms featured here, but
58 of them cannot be seen because of superimposition of the dots

Research study 6

graph of pressure waves during burrowing in lugworms Abarenicola pacificagraph showing pressure waves during defecation in lugworms Abarenicola pacificaInfaunal animals such as lugworms and clams actively engage in digging and constructing burrows, and in ventilating and defecating.  Each type of activity generates pressure waves that are characteristic for that species and for that activity, and the waves can be detected up to 50cm distance from the burrow opening.  Specific activities are identifiable on the bases of amplitude, period, and component waves.  The signals have low frequencies and therefore carry over relatively long distances in the sediments.  Recordings from lugworms Abarenicola pacifica, for example, from implanted pressure sensors near burrows in False Bay, Washington show a record of porewater pressure during burrowing cycles over a 30-min period (see graph upper Left).  Not surprisingly, the authors find that one of the commonest signals recorded for Abarenicola in the filed is that associated with defecation (see graph upper Right).  Wethey & Woodin 2005 Biol Bull 209: 139.

NOTE  the authors also provide burrowing recordings from clams Macoma nasuta  and the polychaete Neanthes brandti. These are shown on the same graph as the lugworms

Research study 7

Given that the burrows of lugworms Abarenicola spp. often extend into anaerobic soils, is there any feature of their construction that might minimise or prevent diffusion of potentially toxic hydrogen-sulphide gas into the burrows?  Analysis of burrows of lugworms and other invertebrates by researchers from the University of Alberta suggests that there are 3 types of burrows with respect to diffusion of oxygen - ones that: 1)  slightly impede oxygen penetration, 2) inhibit oxygen penetration, and 3) enhance oxygen penetration.  They conclude that the basically unlined burrows of lugworms are of the first type; hence, with respect to our question about hydrogen sulphide diffusion, its burrows appear to lack features that would prevent its diffusion into the water of the burrow.  Zorn et al.  2006 Geobiology 4: 137.

NOTE  the authors examine burrow morphology of 7 invertebrates in Willapa Bay, Washington, including lugworms Arenicola marina.  However, as this is a European species, it is assumed that the lugworm they actually worked on is either Abarenicola pacifica or A. vagabunda, probably the former

NOTE  for anaerobic soils the diffusion of oxygen may not be as much an issue as diffusion of hydrogen sulphide.  The 2 gases would likely have similar diffusive properties