Biotic interaction and synecology in a Late Cretaceous coral–rudist biostrome of southeastern Spain

A coral–rudist biostrome exposed in Campanian limestones near the village of Tabernas de Valldigna in south–east Spain was analysed with respect to its palaeontology, sedimentology and palaeoecology. Special attention was given to possible evidence for synecological interactions between corals and rudists. Changes in the rudist shell accretion process are evident in some polished slabs and thin sections and resulted from in vivo contact with coral-colonies. These unusual balcony-like shell protuberances exist where the rudist’s commissure was in contact with corals. They likely represent defence-reactions of rudists against the coral cnidia. Nevertheless, the fossil record of these biotic interactions is rare. This may be due to different growth-rates of rudists and corals, differing shape and size of interacting areas, or different life-spans. In consequence, the discrete ‘window’ of intergroup biotic interaction was small. Sedimentation and resuspension rates were high in the biostrome and corals only established pioneer associations under these unfavourable conditions. A higher diversity of corals is reached, however, when rudists are present. This increase in diversity resulted from the availability of additional ecological niches such as rudist-shell hard substrates and elevation above mobile sediment surface. Rudists on the other hand, received support from stabilisation of their shells through coral encrustation and framework building. In consequence, both groups benefited from their co-existence.