Taphonomic implications of a mussel-barnacle interaction from Southport, Merseyside, United Kingdom

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The study of the Aktuo-Paläontologie of modern shell accumulations may provide important insights of relevance to, particularly, palaeoecology, taphonomy and ichnology. The broad, flat beach at Southport, north-west England, UK, where the sea retreats over 2 km at low tide, is a notable collecting site for shells of allochthonous benthic molluscs. Selected for discussion here is a specimen of the mussel, Mytilus edulis (Linnaeus), which is densely encrusted in two layers on its well-preserved left valve by the barnacle Balanus crenatus Bruguière; the broken right valve has a sparse infestation of this balanid. The valves remain conjoined because the ligament was overgrown by balanids from the left valve, an unusual preservation. The shell was presumably buried, smothering the initial balanid infestation of the left valve; on reexposure, the surface of dead balanids was covered by a new, conspecific layer. For much of its pre- and post-mortem existence, the right valve was probably buried. The superior preservation of the left valve was favoured by the thick, balanulith-like coating of cemented barnacles. The inner surfaces of both valves remained clean and lack any encrustation.