Biodiversity & Conservation

Sabellaria spinulosa crusts on the substratum may be sufficiently dense to prevent the settlement or attachment of other species to the substratum (although the crust may itself act as a substratum). On the horizontal surface of the wreck of the MV Robert off Lundy, Sabellaria spinulosa was an initial colonizer dominating the surface and possibly blocking contaminants from anti-fouling paints. The crust of Sabellaria spinulosa was colonized by a rich community including especially erect bryozoans and hydroids and colonial tunicates (Hiscock, 1981, Hiscock & Rostron, unpublished). The community on the MV Robert is now (revised 2003 classification) recognised as included in MCR.Sspi, now CR.MCR.CSAB.Sspi: Sabellaria spinulosa encrusted circalittoral rock. Ophiothrix fragilis, selected as an important functional species in the biotope, may occur in dense aggregations (George & Warwick, 1985) but more typically in lower densities (Connor et al., 1997(a)). Dense aggregations of brittle stars may also occupy space that could otherwise be taken up by other species. Both Sabellaria spinulosa and Ophiothrix fragilis are suspension feeders. In dense brittle star beds, food availability may be monopolised by Ophiothrix fragilis restricting the growth of other species (George & Warwick, 1985). Urticina felina is a passive carnivore, waiting to trap animals that stumble into its tentacles. Other characteristic species from the biotope are scavengers (Pagurus bernhardus) and detrital grazers (Gibbula cineraria).

Most of the characterizing species in the biotope have a longevity of several years (Davoult et al., 1990; Gage , 1990; Wilson, 1971; Chia & Spaulding, 1972). High recruitment of Sabellaria spinulosa may result in 'reinforcement' of the crust of tubes on the substratum. Winter storms can break up these crusts, particularly if on more mobile substrata. Areas where Sabellaria spinulosa had been lost due to winter storms appeared to recolonize up to a maximum thickness of 2.4 cm during the following summer (R. Holt, pers. comm. in Jones 1998). Potential high recruitment of Ophiothrix fragilis following mild winters (Smaal, 1994) may cause increases in numbers of brittle stars present in aggregations on the ross worm crusts. Ophiothrix fragilis also appears, in some areas, to have a multi-annual (about 4 years) cycle (Davoult et al., 1993). The community described from the wreck of the MV Robert that is recognised as MCR.Spi was described five years after the sinking of the vessel.

Habitat complexity will vary depending on the species composition of the biotope. Dense crusts of Sabellaria spinulosa can provide greater structural complexity to bare bedrock habitats and may consolidate areas with more mobile substrata such as cobbles, or muddy gravels. The crusts can provide a textured substratum, and shelter between tubes etc. Species that burrow into soft substrata may also occur in thick crusts. For a list of associated species in a thoroughly sampled example of a Sabellaria spinulosa crust, see George & Warwick, 1985). However, crusts are often quite bare of other epibiota. The presence of dense aggregations of Ophiothrix fragilis also contributes to increases in structural complexity and considerable numbers of species may utilise these beds (Warner, 1971). Extensive Mytilus edulis has been noted from the biotope in south Wales and these will also increase structural diversity.

George and Warwick, (1985) note that in a hard-bottom reef community with Sabellaria spinulosa, production is overwhelmingly dominated by the suspension feeding Ophiothrix fragilis. Much of this production may be through regeneration of broken arms (Sköld, 1998) Since the biotope is circalittoral, few algae are present and consequently, primary production is low. Sabellaria spinulosa larvae may settle in swarms and result in very high recruitment (Wilson, 1929). Rapid growth in suitable conditions may result in high productivity.

Sabellaria spinulosa, Ophiothrix fragilis and most of the other associated sessile species have planktonic larvae and the potential for dispersal over considerable distances (Wilson, 1929; Davoult et al., 1990). Recruitment of Sabellaria spinulosa is probably enhanced by the presence of adults or even just sand grain tubes of the same species (Wilson, 1929). In areas with considerable water movement, populations of Ophiothrix fragilis probably do not autorecruit due to the long duration (26 days) of the larval stage (Davoult et al., 1990). Ophiothrix fragilis larvae may settle on dense aggregations of adults (Warner, 1971). Some characteristic species may not recruit so readily, for instance the larva of Urticina felina inhabits the water column, but is not considered to be truly pelagic and probably has limited dispersal abilities (Solé-Cava et al., 1994). Areas where Sabellaria spinulosa had been lost due to winter storms appeared to recolonize up to a maximum thickness of 2.4 cm during the following summer (R. Holt, pers. comm. in Jones 1998). Sabellaria spinulosa adults are permanently attached to the substratum so no immigration of adults is possible. Recruitment processes of other species will vary according to the species composition of the biotope which may reflect in some measure the species present in nearby rocky biotopes.

Sabellaria spinulosa recruits readily although environmental conditions can affect success. In ideal conditions, (extrapolated from the similar species Sabellaria alveolata), growth can be rapid and sexual maturity reached within the first year. Other species in the biotope may not be so quick in reaching maturity. For instance, Urticina felina is noted as being a slow growing, large anemone living for several years (Chia & Spaulding, 1972). The smallest recorded fertile anemone was at least 1.5 years old (Wedi & Dunn, 1983). There is considerable debate over the growth rate and longevity of Ophiothrix fragilis. Gage, (1990) worked on growth bands in the skeletal ossicles of the brittle star. Growth rates were estimated to be slow and life span to be at least 10 years, with sexual maturity probably achieved at about 10 mm disk diameter (several years old). Davoult et al., (1990) estimate longevity to be as short as 9 months with development to maturity taking from 6-10 months depending on time of recruitment. The overall time for the community to reach maturity will also depend to some extent on other species in the biotope (sometimes occurring in high densities) e.g. Mytilus edulis (Hiscock, 1979). Other species in this biotope may reflect, in some measure , the species found in nearby rocky biotopes. The community described from the wreck of the MV Robert that is recognised as MCR.Spi was described five years after the sinking of the vessel.

Sabellaria spinulosa appears to occur in high densities and form crusts especially in turbid and polluted waters. It occurs extensively in the Severn Estuary and Bristol Channel (with Sabellaria alveolata) (George & Warwick, 1985) and on tide-swept mobile substrata such as the English Channel (K. Hiscock pers. comm.). It was an initial colonizing species on a wreck off Lundy and was abundant in an area severely polluted by an acidified halogenated effluent (Hoare & Hiscock, 1974).