Factors Affecting Recruitment

Changes to Sand Supply

Cold Winters

Predator Densities

Sabellaria alveolata is well known to be extremely variable in recruitment but the reasons for this are not known. A number of possibilities can be mooted speculatively, such as:

• Lowered fecundity due to environmental factors such as temperature, food supply
• Reduced larval supply due to loss of reefs in neighbouring areas
• Lack of larval supply due to the vagaries of water movements

By virtue of its dependence upon hard substrata adjacent to good supplies of suspended sand, Sabellaria alveolata lives in areas which are subject to large scale changes in sand supply, for example as a result of storms. Wilson (1971) reported regular changes in sand depth of a metre or two metres at Duckpool, North Cornwall. Sabellaria reefs survived short-term burial for days or even weeks but were killed by long-term burial which is probably a frequent occurrence. Burial of reefs has been recorded on the Cumbrian coast (Perkins, 1967) and is almost certainly a common occurrence elsewhere.

In the Mediterranean Gulf of Valencia, Porras et al. (1996) reported losses of S. alveolata reefs due to siltation form river floods and natural accumulation of sand, but that the reefs recovered rapidly (within a few years) in comparison to situations where sand accumulated as a result of human activities.

There were numerous losses of S. alveolata due to the cold winter of 1962-63, particularly in North and South Wales and Lyme Bay (Crisp, 1964). Most appeared to have fully recovered by 1984 (Cunningham et al., 1984). S. alveolata in Criccieth in North Wales was badly affected by the cold winter of 1984 (Gubbay, 1988). Recent information suggests that recovery may have been only limited by 1995 (CCW, unpublished), although due to the variable and sometimes cyclic nature of S. alveolata reefs this conclusion may not be valid if regular monitoring was not carried out in the intervening period. Extensive intertidal reefs are known to have been present in the Dee Estuary (Hilbre Island) in the late nineteenth and early twentieth centuries (eg Herdman, 1919) but were absent when resurveyed during the 1940’s (Craggs, 1982) and 1980’s (Cunningham et al., 1984).

Extreme temperatures may also have the potential to indirectly alter community structures. In the North east Pacific, Paine (1986) observed a change between the dominance of M. californianus before a severe freeze and M. edulis (which is much more tolerant of low temperatures) after. Since there seems frequently to be some competition between S. alveolata and Mytilus edulis, and these have different temperature tolerances, it is possible that low temperatures might play a part in determining which of these species dominates.

There is little knowledge of predators of Sabellaria alveolata, (chapter IV). Sensitivity to changes in predator populations is therefore unclear, but seems unlikely on present knowledge to be an important consideration.

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