||Range of conditions
||Exposed, moderately exposed
||Bedrock; cobbles; boulders; pebbles; sand
alveolata requires a hard substratum on which to form and these areas must have a good
supply of suspended coarse sediment. S .alveolata reefs can form on a range of
substrata from pebble to bedrock (Cunningham et al. 1984). Reefs therefore commonly
form on areas of rock or boulders surrounded by sand.
||Mid shore, Lower shore
Reefs form mainly on the bottom
third or so of the shoreline and in the shallow subtidal. Reefs have been recorded
subtidally in the Severn Estuary and have been assigned a new MNCR biotope code
SalvMx (Moore et al. 1998)
||Gruet (1982) reported that growth of S. alveolata is
severely restricted below 5oC. Crisp (1964) noted severe losses of S.
alveolata due to the severe winter of 1962-63, especially in south and north Wales,
and in Lyme Bay where some colonies were depleted by half and others lost completely.
Survival was best at lower shore levels.
||A supply of suspended coarse sediment is a requirement for
the development of reefs, but the species has been reported to penetrate into areas such
as the Severn Estuary where finer suspended sediments occur (Cunningham et al.
1984). Suspended sediment supply is affected by both the local availability of sediment
and the amount of water movement for its suspension.