| |
S. alveolata |
S. spinulosa |
M. modiolus |
M. edulis |
S. vermicularis |
| Usual habitat |
Rocks, boulders, cobble in intertidal &
shallow subtidal with a good supply of suspended coarse sand |
Turbid circalittoral mixed sediments |
Circalittoral mixed sediments in a variety of
current / wave exposures, varying from open coasts to enclosed sealochs |
Firm mixed sediments in enclosed bays and
estuaries |
Very enclosed sheltered sea lochs, mixed
sediments |
| Geographical distribution of reefs in
Britain |
South and west of Britain only |
Fewer in Scottish waters (all
‘reefs’ including crusts) |
Rare south of Severn & Humber Estuaries |
Widespread |
Loch Creran only |
| Rarity as a species |
Moderate |
Widespread and common |
Widespread and common |
Extremely widespread and common |
Widespread and common |
| Rarity as a reef biotope |
Fairly unusual |
True reefs appear to be rare but less stable
‘crusts’ probably common, less so in Scotland |
Scattered clumps much more widespread and
common than very dense reefs or gravel embedded reefs |
Common |
Extremely rare |
| Natural variations in abundance over
periods of a few years |
Very high |
Crusts annual & probably variable, others
probably more stable |
Low |
Some extremely variable, others quite stable |
Probably low |
| Reproduction & recruitment |
Sexually mature in 1st year. Recruitment very
variable. Settlement strongly induced by contact with adult tubes (living or dead) |
Sexually mature in 1st year. Recruitment often
seems variable. Settlement induced by contact with adult tubes (living or dead) |
Sexually mature after 3-6 years. Recruitment
often variable Juveniles survive best within byssus threads of adults |
Sexually mature in 1st year. Settlement often
a two stage process. Recruitment highly variable |
Sexually mature in 1st year. Preferential
settlement on calcareous structures |
| Richness of associated communities |
Varies from extremely low when colonies are
young to moderate when colonies are older |
Probably high or very high on stable reefs,
less so on crusts |
Very high |
Usually low or moderate but higher than
surrounding areas |
Probably very high |
| Importance of predation |
Not thought to be very important overall
although crab predation was important in transplanted reefs |
Not known. |
Predation by invertebrates very important in
first 3 or 4 years, low thereafter |
Invertebrate and fish predation can be very
high on small animals. Bird predation very high on adults |
Not known. |
| Importance as food for other species |
Probably low overall |
May be moderately important for prawns? |
Probably low overall |
Extremely important for some birds, especially
eiders and oystercatchers |
Probably low overall |
| Known major sensitivities to human impacts |
Possibly major changes to sediment regime
(could be positive as well as negative effects) |
Prawn trawling and probably aggregate
extraction |
Towed bottom gear (eg scallop and queen
scallop dredges and trawls) |
Overexploitation |
Mooring of cages, organic waste disposal. Potentially
queen scallop trawling & diver collection |
| Physical fragility |
Moderate |
Moderate? |
Moderate (low if very recessed?) |
Moderate |
High |
| Recovery after damage |
Probably generally good but possibly not after
large scale losses or at extremes of range |
Probably generally good but not if fishing
impacts continue or if damage is over very wide areas |
Likely to be very slow, and possibly not at
all if completely lost, especially in enclosed areas |
Generally very good but evidence of poor
recovery after widespread losses |
Probably slow, and not at all after large
scale loss |
