Environmental Requirements

Physical Attributes

Specific information on temperature tolerance was not found for this species, but its widespread distribution, from at least North of the Shetlands to the Mediterranean Sea, together with its predominantly subtidal habit means that S. spinulosa is likely to be much less sensitive to temperature changes than the intertidal S. alveolata, which has been shown to be severely affected by low winter temperatures - for example, S. spinulosa was not affected by the cold winter of 1963 although many S. alveolata mortalities resulted (Crisp, 1964).

Although individuals can certainly occur intertidally, very dense S. spinulosa is found almost entirely subtidally; there are no reports of intertidal reefs in Britain though sporadic dense intertidal reefs have been reported from the Waddensee, southern North Sea (observations of Linke, 1951 discussed by Wilson, 1971; see chapter IV). Dense crusts are reported in the infralittoral and may occur in only a few metres of water; they are also found in the circalittoral but the maximum depth of dense crusts is unclear. Dense reefs reported by George & Warwick (1985) in the Bristol Channel were in 41 m of water while recently discovered reefs in the mouth of the Wash are in 15-25 m (Foster-Smith et al., in prep February 1998).

S. spinulosa requires suspended sand grains in order to form its tubes; reef communities therefore only occur in very turbid areas where sand is placed into suspension by water movement. The relative importance of tidal versus wave induced movements is unclear.

S. spinulosa reefs or crusts will form on hard substrata but this does not preclude their formation on other substrata (Hiscock, 1991 and pers. comm.).

Several sources suggest that bedrock is not necessary for formation of Sabellaria spinulosa crusts and reefs, though a somewhat firm substratum is presumably required. Rees & Dare (1993) describe habitat/ distribution as being typically on shell (especially oyster valves), sandy gravel or rocky substrata with moderate to strong tidal flow. Larsonneur (1994) reported that Sabellaria spinulosa dominated communities were present on rock/pebble bottoms in the Bay of Mont St Michel. He also reported sand masons Lanice conchilega could sufficiently stabilise sand to allow colonisation by S. alveolata. It can be speculated that the same process might be possible with Sabellaria spinulosa too, since Lanice and S. spinulosa are sometimes found together (e.g. Foster-Smith et al., 1997) and extensive S. spinulosa colonies are known to occur in essentially sandy areas (see below); this has not been demonstrated, however. Numerous studies have reported high densities of S. spinulosa in Day grab or other grab samples which would be unlikely from hard bottoms (Foster-Smith et al., 1997). Hoare & Hiscock (1974) reported the presence of S. spinulosa associated with kelp holdfasts (which themselves require a hard substratum).

Larvae are strongly stimulated to settle by cement secretions of adult or newly settled S. spinulosa (see chapter IV). In the absence of suitable stimulation metamorphosis and settlement occurs but always more slowly (Wilson, 1970).

There is some suggestion from field observations that established colonies can increase in extent by addition to the existing colony without the need for hard substratum; Warren & Sheldon (1967), Schafer (1972) and Warren (1973) have reported extensive Sabellaria spinulosa colonies in essentially sandy areas.

It is likely that stability of the reefs is to some degree a function of stability of the substratum. The more transient crusts probably occur principally on relatively unstable substrata such as mobile sands, while longer lasting reefs could be limited to more stable substrata such as firm mixed sediments.

Little firm information was found on salinity requirements of S. spinulosa although well developed reefs seem to be restricted mainly to deeper waters where salinity would be expected to be more or less fully marine. However, McIntosh (1923) referred to dense aggregations of Sabellaria (alveolata) being particularly common in estuaries such as the Tees and Humber. Given that his drawings of the aggregates of Sabellaria from the Humber looked more like S. spinulosa than S. alveolata, and the known distribution of the Sabellaria species, it seems these aggregations were almost certainly misidentified S. spinulosa.

The fragility, or otherwise, of substantial reefs is unclear, although according to Wilson (1970) the tubes of Sabellaria spinulosa are harder and stronger than those of S. alveolata. However, S. spinulosa reefs in the form of widespread sheets are probably surprisingly fragile. George & Warwick (1985) mention that reefs are broken up sufficiently easily to be sampled by a Day Grab, which is usually unsatisfactory for obtaining samples on hard or stony grounds. Attrill et al. (1996) also obtained samples of S. spinulosa reefs which they regarded as quantitative using a Day grab, as did NRA (1994). R. Holt (pers. comm.) has observed that crusts of S. spinulosa on cobble and boulders off the Northumberland and North Yorkshire coasts often break up during winter storms. Elsewhere, however, they do seem to be more permanent features, although this may be mainly related to the stability of the physical environment in which they are found rather than any inherent biological difference. The ‘balls’ of S. spinulosa found by Attrill (pers. comm.) are probably considerably more robust, although there is no published evidence for this. There is much evidence that reefs can be very badly broken up by fishing (chapter VI). The fragility, or otherwise, of substantial reefs is unclear.

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