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.
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 is rapid, and is promoted by high levels of suspended sand and
by higher water temperatures up to 20°C. 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.
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
Wilsons 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.
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.
No information was found regarding community structure of subtidal S.
alveolata reefs, and the following information therefore relates entirely to
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
No rare or unusual species have been reported to be associated with Sabellaria
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
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.