Changes in Sediment Regime

Physical Damage

Aquaculture

Chemical Contaminants

Cooling Water Discharges

It would be expected that this species would be sensitive and vulnerable to changes in sediment regime, and this certainly appears to be the case. There is some evidence that newly constructed groynes off Morecambe have resulted in a coarser sediment regime which has allowed S. alveolata to colonise boulder and cobble grounds in place of Mytilus which was previously dominant (Lumb, pers. comm.; Andrews, pers. comm.).

In the Mediterranean Gulf of Valencia, Spain, 23 sites at which S. alveolata reefs had been reported since 1989 were resurveyed in 1994. Reefs were found at only 13 sites, and of these there was clear evidence of reduction in extent in three and increase in extent at four (Porras et al., 1996). They reported that the most frequent cause of losses was sand level rise as a consequence of the construction of sea walls and marinas / harbours, and beach nourishment projects. Although reef losses were also attributable to natural causes such as river floods or natural sand accumulation, in these cases, recovery after perturbation events had been recorded on many occasions between 1989 and 1994.

On more open coasts, where shore defences on one stretch of coast are able to reduce sand supply to neighbouring areas, it may be speculated that this might lead to reduced availability of sand and therefore reduced development of S. alveolata reefs. Parts of the Cumbrian and Welsh coasts might conceivably be susceptible to such changes. Modern policy tends to be not to carry out activities which might result in dramatic reductions in sediment supply to neighbouring areas, but the possibilities should nevertheless be borne in mind.

Trampling and, possibly, bait digging have been identified as possible impacts (e.g. Cunningham et al., 1984). Cunningham et al. (1984) showed rapid recovery from single trampling events of a light or moderate nature. More extensive damage to colonies (i.e. chunks being removed) was less evident in the short term, but some such damage did occur and was subsequently enlarged by wave action. Mitchell (1984) observed that in Brittany damage on popular beaches was minimal and limited to trodden gaps for access through the reefs. Damage to colonies has been observed by people breaking open the tubes with knives and removing the worms for use as fishing bait, though nowhere has this been seen on any intensive scale (Cunningham et al., 1984; Hawkins, pers. obs.).

  Aquaculture

In Brittany intensive mussel cultivation on ropes wound around intertidal oak stakes affected nearby S. alveolata reefs in three ways: they were smothered with faeces and pseudofaeces, (though it was not clear if this resulted in any harm); small mussels dislodged from the ropes then lodged in the reefs and broke up the surface as they grew; and commercial collection of these mussels from the reef caused trampling damage (Mitchell, 1984). However, mussels are extremely common in cSACs where extensive Sabellaria reefs are found and nearby cultivation activities (which would probably be limited to relaying) seem unlikely to have detrimental effects. Relaying directly on top of Sabellaria reefs would, of course be detrimental but seems unlikely to be attempted.

Mitchell (1984) stated that one of the prime reasons for initiating the research carried out by Cunningham et al. (1984) was "reports of the species vanishing from some areas due to pollution" but no further information on this has been found. S. alveolata were, however, common at the turn of the century at Hilbre Island in the mouth of the Dee Estuary, but disappeared for reasons unknown; siltation, cold winters and pollution have all been quoted as possibilities (Craggs, 1982), though there was no apparent justification for the latter.

S. alveolata appears to be present at lower abundance on that part of the Cumbrian coastline where industrial and sewage effluents are most concentrated (around the Whitehaven - Workington - Maryport area) than elsewhere on the Cumbrian coast, but to some extent this might simply represent a lack of suitable habitat (Hartnoll et al., 1998).

Possible evidence of sensitivity to detergents used in oil spill events was found for the larvae of S. spinulosa, to which is closely related (see below), though no references were found for S. alveolata itself.

Overall there is little evidence for any unusual sensitivity to chemical contaminants.

Studies at Hinkley Point, Somerset, found that growth of the tubes in the winter was considerably greater in the cooling water outfall, where the water temperature was raised by around 8-10° C, than at a control site, although the size of the individual worms themselves seemed to be unaffected (Bamber & Irving, 1997).

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