The lugworm, Arenicola cristata, is a large cigar-shaped polychaete with 17 setae-bearing segments (Voss 1980). The surface of the body is roughly textured and green to brownish-green in color. Three body regions are apparent when examining the appearance and behavior of the lugworm (Ruppert & Fox 1988). The front region is a muscular portion primarily used for digging. Eleven pairs of bushy red gills cover the middle of the body, which controls respiration (Kaplan 1988; Ruppert & Fox 1988). Excretion occurs at the back, which is usually the only portion visible above the sediment when the worm is buried.
Potentially Misidentified Species
Several polychaetes are found in the sediments of the IRL. However, the lugworm can be distinguished from similar species by its size, body form and coloration, and the shape of its burrow. Many other segmented worms in local waters bear specialized structures like ornate gills, tentacles, or bristles that aid in their identification (e.g. Voss 1980; Ruppert & Fox 1988).
HABITAT AND DISTRIBUTION
The range of A. cristata extends on the Atlantic coast of the U.S. from Cape Cod to Florida, throughout the Caribbean and the Gulf of Mexico (Kaplan 1988). Lugworms reside in U-shaped burrows they excavate in undisturbed sandy or muddy sediments on protected beaches and tidal flats (e.g. Ruppert & Fox 1988; Woodin et al. 1995; Marinelli & Woodin 2002). The anterior end of the burrow becomes depressed as the worm ingests surface sediment in search of organic material on which it feeds. A mound of waste material and undigested sand is deposited at the opposite end of the burrow (Voss 1980). See ‘Trophic Mode’ below for more information.
Little information is available concerning populations of A. cristata in the IRL, but worms can be found throughout the lagoon in the sediments of sheltered beaches and tidal flats. Studies have been conducted on worms found near Harbor Branch Oceanographic Institution in St. Lucie County, at Sebastian Inlet, and in the northern IRL at Titusville (Peyton et al. 2004).
LIFE HISTORY AND POPULATION BIOLOGY
Age, Size, Lifespan
The lugworm typically grows to a length of about 10 cm (Voss 1980), though some individuals can exceed 30cm in length with a diameter of 1.5cm (Ruppert & Fox 1988). Lifespan varies with environmental conditions and other factors.
Details on the abundance of A. cristata in the IRL are scarce, but densities of up to 5 individuals m-2 were found for lugworm populations in Tampa Bay, Florida (Bloom et al. 1972).
Reproduction & Embryology
In the spring, the lugworm produces a gelatinous pink egg mass, nearly one meter long. The mass is connected at one end to the burrow opening, with the remainder swaying freely in the current like a streamer (Ruppert & Fox 1988). Some smaller individuals in sandy sediments may produce a compact ovoid or spherical egg mass instead. Embryonic development observed in the laboratory for egg masses held at 21°C was documented at 4-5 days, with a hatching time of 1-2 days (Peyton et al. 2004). The larvae of the A. cristata are lecithotrophic, subsisting off limited energy stores before developing to a point when they are obligated to feed. This developmental mode allows the larvae more dispersal time as plankton in the water column before they must find a suitable habitat and settle to the benthos, a period of about 2-4 days for most larvae (Richmond & Woodin 1996).
Lugworm egg masses are also known to have a symbiotic relationship with diatoms fouling the exterior of their cases. Studies have suggested that the masses supply substratum for settlement of the diatoms, while oxygen produced by the microscopic algae provide buoyancy for the eggs, lifting them off the sediment and protecting them from benthic predators such as the bruised nassa snail, Nassarius vibex (Peyton et al. 2004).
Based on its range, the lugworm likely prefers and/or requires warmer temperate to tropical waters in order to thrive.
Lugworm populations can be found in a variety of salinities, from brackish estuaries to coastal marine waters. However, studies have shown that growth and development is hindered for larvae cultured under short-term salinity reductions down to 15 ppt, with larval mortality peaking when salinities dropped to 10 ppt and below (Richmond & Woodin 1996). Subsequent studies revealed that the oxygen consumption of individuals at these reduced salinities was significantly lower than that of their counterparts held under more saline conditions, suggesting that respiration plays a role in the salinity tolerance and preferred range of this species (Richmond & Woodin 1999).
Lug worms are known as non-selective deposit feeders (Bloom et al. 1972), consuming subsurface sediment and defecating undigested material at the entrance of their burrows in the form of fecal castings that resemble those produced by sea cucumbers or the acorn worm, Balanoglossus aurantiacus (Ruppert & Fox 1988). Like terrestrial earthworms, this feeding method serves the important function of tilling sediments to promote aeration of soils and decomposition of organic material.
Fishes and other invertebrates may attack the hind end of the lugworm as it exits the burrow. In such an event, A. cristata has the ability to cast off and regenerate these segments in order to avoid predation, much in the same way a lizard sacrifices its tail or a crab drops a leg to escape predators (Ruppert & Fox 1988). Lugworm eggs masses are preyed upon by a variety of benthic organisms, such as the bruised nassa, Nassarius vibex (see ‘Reproduction & Embryology’ above).
Lugworms often share their borrows with the commensal pea crab, Pinnixa cylindrica (Ruppert & Fox 1988). The tiny crab reaches about 1.5 cm in length, and likely lives within the worm burrow for protection.
In addition to relationships formed between adult worms and other organisms, several species of microalgae grow symbiotically on the surface of lugworm egg masses (see ‘Reproduction & Embryology’ above).
The green color of the lugworm results from the presence of a class of chemicals called quinones (Ruppert & Fox 1988). Despite the antibiotic properties of these compounds, little information is available on the feasibility of isolation and/or synthesis of this natural product for medicinal purposes.
Because it is an infaunal species, burrowing in and consuming the sediment, A. cristata is used as an indicator species for the presence and effects of environmental contaminants and pollutants reaching benthic marine habitats from sources such as coastal runoff and ship traffic (e.g. Schoor & Newman 1976; Walsh et al. 1986).
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