Sabellaria alveolata

Biology

Ecological Functioning

Reproduction, development and growth

Longevity and stability

Feeding

Parasites and diseases

Reef habitats

Predators

Competitors

Wider effects on the environment

 

Reproduction, development and growth

The most detailed work done on S. alveolata reproduction within Britain is that of Wilson (e.g. Wilson, 1971) in Cornwall.

Spawning season

Wilson (1971) reported a short summer spawning period around July.

Larval development and settlement

The larvae probably spend anything between 6 weeks and 6 months in the plankton (Wilson, 1968b; Wilson, 1971) so that dispersal could potentially be widespread. Slight settlement has been observed in all months except July, but in 14 years of close observations (1961 to 1975), Wilson (1976) observed only three heavy settlements, in 1966, 1970 and 1975. All were in the period from September to November or December. Observations elsewhere also support the observation that intensity of settlement is extremely variable from year to year and place to place (Cunningham et al., 1984; Gruet, 1982). Settlement occurs mainly on existing colonies or their dead remains; chemical stimulation seems to be involved, and this can come from S. spinulosa tubes as well as S. alveolata (Cunningham et al., 1984; Gruet, 1982; Wilson, 1971).

Growth rates

Growth is rapid, and is promoted by high levels of suspended sand and by higher water temperatures up to 20C. A mean increase in tube length of up to 12 cm per year has been reported for northern France (Gruet, 1982). Cunningham et al. (1984) stated that growth is probably lower than this in Britain due to the lower water temperatures, although Wilson (1971) reported growth rates (tube length) of 10-15 cm per year in several colonies at Duckpool, North Cornwall for first year colonies, and around 6 cm in second year worms.

iv. Maturation

Wilson (1971) reported that in good situations the worms mature within the first year, spawning in the July following settlement.

 

Longevity and stability

A typical life span for worms in colonies forming reefs on bedrock and large boulders in Duckpool was 4-5 years (Wilson, 1971), with a likely maximum of around 9 years (Gruet, 1982; Wilson, 1971). However, it is suspected that there are many colonies on intertidal cobble and small boulder scars on moderately exposed shores where shorter lifespans are likely due to the unstable nature of the substratum. Wilson (1971) reported that it was possible to age the worms to some degree by measuring the diameter of the tube (but not the wider ‘porch’ at the top of the tube).

Cunningham et al. (1984) reported that no observations appear to have been made on the longevity of actual reefs rather than individual worms, although in fact Wilson’s observations at Duckpool, North Cornwall do contain some useful information in this regard, as do some less detailed studies by other workers. There is plenty of evidence that intertidal reefs, at least, are in many cases unstable, and there frequently (but by no means always) appears to be a cycle of development and decay over periods of up to around five years (Gruet, 1985; Gruet, 1986; Gruet, 1989; Perkins, 1986; Perkins, 1988; Perkins et al., 1978; Perkins et al., 1980). Exceptionally, Wilson (1976) observed one small reef from its inception as three small individual colonies in 1961, through a period between 1966 and 1975 where it existed as a reef rather greater than 1 metre in extent and up to 60 cm thick, with major settlement of worms occurring in 1966 and 1970. This reef finally ‘died’ in the autumn of 1975, ironically a period of intense new settlement elsewhere the same beach (Wilson, 1976). In the long term, areas with good Sabellaria reef development tend to remain so.

 

Feeding

S. alveolata is a filter feeder, but no information on feeding biology or mechanisms in this species was found. Wells (1970) described briefly the feeding structures and mechanisms of the related intertidal reef builder Sabellaria kaiparaensis. There was no information on particle size preferences or the effect of external factors such as food availability or turbidity on feeding, but a crude sorting mechanism was described, whereby particles too large to be ingested glide over the mouth and are transferred via the ventral lips to specialised pads which incorporate them into the walls of the tube. It was also mentioned that the worms did not feed continuously without aeration because suspended matter would foul the ciliary mechanism under stagnant conditions. In the absence of more specific information it has to be assumed that these observations also apply to S. alveolata and S. spinulosa.

Parasites and diseases

No information was found on this subject.

Ecological Functioning

Reef habitats

No information was found regarding community structure of subtidal S. alveolata reefs, and the following information therefore relates entirely to intertidal reefs.

Intertidal S. alveolata reefs are not particularly diverse communities, though they do nevertheless provide some increased diversity of habitat, and older reefs have somewhat more diverse associated communities than younger ones.

Sheets of S. alveolata appear to enhance algal diversity, apparently by providing barriers to limpet grazing (Hawkins, pers. obs. in Torbay and Cunningham et al., 1984). A number of studies have reported that older reefs provide a variety of habitats for other species, often in crevices. Wilson (1971) noted that Fucus serratus, F. vesiculosus, Palmaria palmata, Polysiphonia sp, Ceramium, sp, and Ulva lactuca are frequently associated with older Sabellaria colonies, and small polychaetes such as Fabricia sabella and syllids have been found living within the colonies. Cunningham et al. (1984) carried out limited quantitative quadrat surveys of S. alveolata reefs and noted up to eighteen associated animal species and twenty associated plant species, mainly on older colonies. The important animal species were all epifauna, including barnacles Chthamalus montagui, C. stellatus and Semibalanus balanoides, limpets Patella vulgata, P. depressa and P. aspera, mussels Mytilus edulis, dogwhelks Nucella lapillus and serpulid worms. There were few crevice fauna. The important plant species were Ceramium sp, Fucus vesiculosus, F. serratus, Ulva lactuca, Laurencia sp, Palmaria palmata, Corallina elongata, Enteromorpha sp, and Lomentaria sp. They found that algal colonisation, particularly of Ulva and Enteromorpha, was higher on reefs with a placages (sheet) structure, which they attributed to the fact that the worm tubes grow more longitudinally than in other reefs, so that algal sporelings are less likely to be disturbed by the growth or feeding activities of the worms. It is suspected that detailed studies would reveal other differences between the various physical forms of S. alveolata reefs.

Most studies have suggested that dense young colonies of Sabellaria alveolata are not very diverse communities. Wilson (1971) noted that barnacles, serpulid worms, encrusting algae and smaller tufted algae are overgrown and smothered out of existence by S. alveolata, that even algae do not do well where the Sabellaria are in their prime, and that where Sabellaria are dominant other species are suppressed. He stated that the reefs were at their ‘best and cleanest’ (i.e. well developed, contiguous reefs not overgrown by encrusting or attached fauna and flora) when a majority of worms in them were aged around 2 years. At Risehow Scar in Cumbria it was observed that "it has covered much of the scar and by firmly cementing gravels, shingle cobbles and boulders into a coherent layer it has reduced diversity and abundance of fauna eg littoral fish, small crabs and molluscs which have nowhere to shelter when the tide is out" (Perkins, 1988). Cunningham et al. (1984) reported that actively growing Sabellaria colonies are able to outcompete all other littoral species for space, and noted that young sheets of S. alveolata may reduce the diversity of shores by reducing the number of crevices available, but that as the sheets get older and break up the range of habitats provided increases. Thus the overall diversity of the community seems in general to be closely related to the developmental cycle of the reefs, as noticed also on French shores by Gruet (1982).

Cunningham et al. (1984) also noted that placages may impede the drainage of the shore, creating pools of standing water where there would otherwise be none. Further habitat modification they reported included the stabilisation of mobile sand, shingle, pebbles, and small boulders, for example on the Cumbrian coastline, and increased habitat heterogeneity of exposed barnacle dominated shores and sand scoured rocks.

No rare or unusual species have been reported to be associated with Sabellaria alveolata reefs.

Predators

There is little detailed mention in the literature of predation on Sabellaria alveolata, although Carcinus maenas was a troublesome predator of transplanted portions of reefs in Somerset (Bamber & Irving, 1997), and remains have been found in the stomachs of the shore crab Carcinus maenas and the blenny Blennius pholis on shores at Sellafield, Cumbria (Taylor et al., 1962). Herdman (1919) mentioned that flatfish such as plaice and sole could easily obtain the worms by crunching up the brittle sand tubes but this appears to be supposition. Since the worms are known to be able to retract considerable distances down into the tubes (Cunningham et al., 1984; Wilson, 1971), it would appear to be difficult for predators to extract worms easily from compact reef masses. Bird predation has never been mentioned in any reports found by the authors, so it seems likely that the main predators are marine organisms. Wilson (1971) seemed to regard predation on S. alveolata reefs in North Cornwall as of little overall importance.

Competitors

Stability of Sabellaria reefs is influenced not only by stability of the substratum on which they are settled, but perhaps also by interactions with other species. It has been reported that heavy mussel settlement on reefs in Cumbria caused some deterioration in the quality of the reefs (Perkins, 1988). It has also been observed in Brittany that small mussels dislodged from nearby cultivation ropes lodge in the reefs and break up the surface as they grow (Mitchell, 1984). Cunningham et al. (1984) noticed large numbers of mussels particularly on older Sabellaria colonies, and suggested the existence of a Sabellaria / Mytilus succession, though they conceded that long-term observations were necessary to confirm this. Further support for this theory has come in recent years from Heysham, in Morecambe Bay, where Sabellaria reefs have developed on a boulder scar which has for around thirty years normally been populated by mussels Mytilus edulis. It is suspected that changes in sediment regime, including increased availability of coarse sand, as a result of a number sea defence developments, have allowed Sabellaria to outcompete the mussels, though this is unproven (Chris Lumb, Neil Fletcher and Jim Andrews, pers. comms.).

It is also suspected that on older reefs dense growths of seaweeds, mainly Fucus, can cause reefs to be torn up, particularly on less stable substrata.

Wider effects on the environment

No information was found on this subject with regard to S. alveolata.

Next Section                     References