Taphonomic signatures on the pearl oyster Pinctada from Arabian Gulf, Saudi Arabia

Abstract

A total of 886 valves of the pearl oyster Pinctada were collected from 12 sites in Al-Uqair beach along the Saudi Arabian Gulf coast in January 2021 in order to document their taphonomic signatures. Thirteen ichnospecies of 5 ichnogenera were identified and illustrated. These traces were produced by clionid sponges (Entobia cretacea, E. ovula, E. geometrica, E. laquea, E. cateniformis, Entobia isp.), durophagous drillers (Oichnus paraboloides, O. ovalis, O. simplex, and Oichnus isp.), traces of vermetid gastropods (Renichnus isp.) polychaete annelids (Caulostrepsis isp.) and barnacle attachment scars (Anellusichnus circularis). The Pinctada shells act as hard substrate for colonization by serpulid worm, Spirorbis sp., bryozoans, barnacles, and other bivalves. Ichnogenus Oichnus was the most abundant (53.73%), followed by Entobia (44.58%), Anellusichnus (0.51%), Caulostrepsis (0.34%), and Renichnus (0.84%). The thin-shelled and smooth skeletons of Pinctada were preferable for the abundant durophagous drillers (Oichnus traces) and clionid sponges (Entobia traces) during the lifetime of the pinctadas, in contrast to endolithic bivalves (Gastrochaenolites borings) which need thicker seashells for the settlement. Occurrence of different encrusters and bioeroders on the internal surfaces of many pinctadas confirmed the postmortem origin of the signatures. Disarticulation, fragmentation, and abrasion among the collected pinctadas might be attributed to their mode of life as epifaunal byssate, filter-feeder bivalves in the shallow littoral and sublittoral zones of the continental shelf under strong currents conditions.