Article: Live and dead faunas from coralline algal gravels, Co. Galway
Daniel W. J. Bosence
A visual assessment, supported by multivariate statistical analysis, of the fauna from seventy-one benthic samples from Mannin Bay shows the existence of five communities, which are coincident with the sedimentary facies of the area. The Bank Community is found in algal banks constructed by the free-living corallines Lithothamnium corattioides and Phymatolithon calcareum. This community is characterized by a varied and abundant epifauna living on the algal thalli. The Muddy Algal Gravel Community also has a rich epifauna but has a more diverse burrowing infauna. The Clean Algal Gravel Community is found in high-energy areas and has a poorer epifauna but a specialized burrowing infauna. The Fine Sand Community is distinct from the algal gravel faunas, being composed of sand-living bivalves, echinoderms, and gastropods. The Mud Community is very poor in both species and numbers. The fauna from Mannin Bay is similar to communities described from coralline algal sediments of Ireland, Brittany, and the English Channel.The post-mortem history of abrasion, encrustation, and boring of the skeletal material is described. The dead fauna is analysed to ascertain whether the previously defined communities are recognizable from the skeletal debris. Most of the dead molluscan species in a facies are exotic but the bulk of the individuals come from that facies. Exotic species are most dominant in the Clean Algal Gravel Facies and the Fine Sand Facies. Gastropods from the rocky substrates form the most abundant group of exotic species. The trophic nuclei of the benthic communities cannot be reconstructed from the dead fauna even though the live faunas are dominated by skeletal organisms. Multivariate statistical analysis shows that the living communities cannot be reconstructed from the dead fauna.