I have written this article in 2009 as part of my Bachelor on Evolutionary Biology at the University of Groningen. This essay aims at providing some basic information about Arenicola marina.

Abstract

The lugworm Arenicola marina is an important biosystem engineer found on the muddy shores on the west coast op Europe. This 15 – 25 cm long annelid lives in burrows in the sediment where it filter-feeds on organic material in the sand. Arenicola marina is gonochoristic and annual iteroparous, showing synchronized spawning in the fall. The worms are sexually mature at 2 – 3 years of age. The juveniles live in cocoons attached to the sediment until they created their own burrow.

Introduction to lugworms

The lugworm Arenicola marina is an important biosystem engineer in the muddy tidal flats of the west coast of Europe (helpdeskwater.nl a). By bioturbation it changes the upper layer of the mud flat significantly, enabling other organisms to live there. The amount of oxygen in the sediment is greatly increased by the bioventilation of A. marina. The lugworm also serves an economical purpose, by being the most important product to bait shops in the UK and other countries.

Arenicola marina belongs to the Annelida; Polycheata: Arenicolidae.

What does a lugworm look like?

This species of Annelid worm has 6 segments with bristles at its head-region, followed by 13 segments with bristles as well as external gills. The rest of the worm is thinner and does not have bristles or gills. It has a proboscis that can be projected outwards. It does not have eyes or eye-spots.
This species of lugworm measures approximately 15 to 25 cm from head to tail when adult (Riisgård and Banta, 1998). There have been reports stating that Arenicola marina can live up to 8 years, but more reliable data is necessary (Waterwereld.nu).

Natural habitat and feeding of lugworms

The lugworm Arenicola marina inhabits muddy shore habitats from Northeren Europe to the Mediterranean. It is commonly found in densities of approximately 20 to 40 individuals per m2. It prefers clean to fine intertidal and shallow subtidal sand.

The lugworms live in a U-shaped or J-shaped burrow, approximately 20 to 30 cm deep into the sediment. The lugworms pump water into their burrow for their oxygen requirements by peristaltic movements of their body. One lugworm can pump up to 430 ml water per hour though their burrow (Baumfalk, 1979A). Water enters though the tail-shaft and leaves the burrow through the head-shaft. The tail shaft is open, but the head-shaft is filled with sediment. The worm ingests sediment from the head-shaft, and digests the organic compounds that are found in this sediment. It defecates all indigestible materials to the surface via its tail-shaft. On the tidal flat this can be found in distinctive heaps of feces called fecal mounds.

At a density of 30 individuals per m2, the lugworms turn over the top 15 cm of the Wadden Sea sediment each year (Cadée, 1976).

Fig. 1. Arenicola marina in it’s burrow. After a drawing by Volkenborn, 2005.

Predators of lugworms

Lugworms are predated by a number of fish, crabs, predatory worms and birds. Cod, flatfish and crabs will eat the tail region of the lugworm when it sticks it out of the sediment to defecate (soortenbank.nl). The lugworms can regenerate this tail region in a few days. There have been reports that the tail of the lugworm gets eaten 2 to 4 times a month (Helpdeskwater.nl a). A number of wading birds also eat the tail region of the worm, but are also capable of digging up the whole lugworm (helpdeskwater.nl a).

Reproduction and development of worms

Arenicola marina is gonochoristic and annual iteroparous. They are sexually mature at 2 to 3 years of age (Howie, 1984).
The Arenicola marina lugworm spawns in the late autumn (mid-October to mid-November), triggered by a temperature drop. All adult individuals spawn synchronously in a single spawning event over a period of 4 to 5 days. At low tide, the females release their oocytes into their burrow and the males release their sperm on top of the sediment. When high tide comes, the sperm are washed into the burrows of the females and fertilization takes place (Watson, 2000).

Early development of the zygotes also takes place in these burrows. After a few weeks of development, the tide takes them out of the burrow (Fish, 1996). They live through winter in mucus tubes or cocoons attached to seaweed or the sediment and feed on organic material. When spring comes, they have reached 6 mm in length and leave their tube. They settle on muddy sediment high in the tide region, where they created a burrow of their own. When autumn comes again, they have reached a size of approximately 3 to 6 cm in length. When winter comes, the juveniles move to lower regions of the tidal flat where the adults also live. They migrate by S-shaped swimming movements, mostly at night (Helpdeskwater.nl b).

References of this article

• Baumfalk, Y.A. 1979. Heterogeneous grain size distribution in tidal flat sediment caused by bioturbation activity of Arenicola marina (Polychaeta). Neth. J. Sea Res. 13: 428-440.
• Cadée, G.C., 1976. Sediment reworking by Arenicola marina on tidal flats in the Dutch Wadden Sea. Neth. J. Sea Res. 10, 440-460.
• Fish, J.D & Fish, S (1996) ‘A Students guide to the seashore’ 2nd Ed. Cambridge University Press.
• Howie, D.I.D (1984) ‘The reproductive biology of the lugworm Arenciola marina’ Fortschritte der Zoologie, Band 29 – Fischer/Pfannenstiel: Polychaete reproduction, Gustav Fisher Verlag, New York.
• Riisgård, H.U., Banta, G.T., 1998. Irrigation and deposit feeding by the lugworm Arenicola marina, characteristics and secondary effects on the environment. A review of our current knowledge. Vie Milleu 48, 243-257.
• Volkenborn, N. 2005. Ecosystem engineering in intertidal sand by the lugworm Arenicola marina.
• Watson, G.J., Williams, M.E., Bentley, M.G. 2000. Can synchronous spawning be predicted from environmental parameters? A case study of the lugworm Arenicola marina. Marine biology, 136: 1003 – 1017
• www.waterwereld.nl, visited at 28 December 2008.
  http://www.waterwereld.nu/zeepier.php
• www.helpdeskwater.nl, (a) visited at 28 November 2008 http://www.helpdeskwater.nl/waterbodems_(ecb)/zoute_baggerspecie/uitleg/bio-assays/arenicola_marina
• www.helpdeskwater.nl, (b) visited at 27 December 2008. PDF “Arenicolamethode”
  http://www.helpdeskwater.nl/aspx/download.aspx?PagIdt=14251&File=arenicolamethode.pdf
• www.soortenbank.nl, visited at 25 November 2008 http://www.soortenbank.nl/soorten.php?soortengroep=duikgids&id=79