A summary of some of the major biological, ecological and sensitivity features of biogenic reefs according to presently available knowledge.

  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