Mytilus edulis beds on reduced salinity tide-swept infralittoral rock
Ecological and functional relationships
Mussels appear to provide the predominant substratum in this biotope but no information has been found on any species living amongst the mussels or infaunal components in sediments. The mussel shells are colonized by epibiota - species that can survive reduced (but not necessarily 'low') salinity. Most species are suspension feeders and so do not interact but the predatory starfish Asterias rubens is likely to have a major effect on survival of the mussels. Kautsky (1981) examined subtidal mussel beds in the Baltic Sea and reported that mussels were a major food source for the flounder (Platichthys flesus) but probably of only minor importance for eelpout (Zoarces viviparus): both species that might occur in this biotope.
Seasonal and longer term change
The dominant species in the biotope can be present throughout the year except for filamentous brown and any other algae which most likely show seasonal change related to light levels. It is possible that some species in the biotope will be killed by low salinity during heavy rain in the winter. Asterias rubens
is known to 'invade' mussel biotopes and cause high mortality but no such changes have been noted specifically for this biotope. Kautsky (1981) reported that no major fluctuations in distribution and abundance of Mytilus edulis
was noted in the Baltic Sea over a ten year period. However, his studied population was not significantly affected by predation.
Habitat structure and complexity
The mussels provide hard substratum for a range of algae and invertebrates to settle and interstices for polychaete worms and other mobile biota to live. If sediments are present amongst the mussels, infaunal burrowing species will be supported.
Mussels can be very fast growing (high productivity).
All of the species named in the biotope and most likely the majority of species occurring in the biotope have planktonic propagules and are likely to settle readily. Recruitment in many Mytilus sp. populations is sporadic, with unpredictable pulses of recruitment, possibly from the pool of young mussels on filamentous algae (Seed & Suchanek, 1992). Mytilus sp. is highly gregarious and final settlement often occurs around or in between individual mussels of established populations. Competition with surrounding adults may suppress growth of the young mussels settling within the mussel bed, due to competition for food and space, until larger mussels are lost (Seed & Suchanek, 1992).
Persistent mussel beds can be maintained by relatively low levels of recruitment. McGrorty et al., (1990) reported that adult populations were largely unaffected by large variations in spat fall between 1976-1983 in the Exe estuary.
Time for community to reach maturity
In the tidal rapids or tidal sound habitat where this species is most likely to occur, productivity and growth are likely to be high. Mussels will grow rapidly but associated species will settle at a particular time of year so that it would take in excess of one year for the community to reach maturity.
This review can be cited as follows:
Mytilus edulis beds on reduced salinity tide-swept infralittoral rock.
Marine Life Information Network: Biology and Sensitivity Key Information Sub-programme [on-line].
Plymouth: Marine Biological Association of the United Kingdom.
Available from: <http://www.marlin.ac.uk/habitatecology.php?habitatid=259&code=1997>