Comparison of sclerobiont communities between three brachiopod host species from the Upper Ordovician Fairview Formation, Eastern USA

Sclerobionts are organisms that encrust onto or bore into a hard substrate. They are valuable sources of palaeoecological data as they often preserve the skeletonized portion of in situ communities from which evidence of host-sclerobiont or sclerobiont-sclerobiont interactions can be extracted. Sclerobiont data also provide useful information related to the life habits of their hosts. Although much work has been done on sclerobionts, those from the Ordovician are understudied. The sclerobiont communities on three brachiopod host species from the Ordovician Fairview Formation (Eastern United States), Rafinesquina alternata, Vinlandostrophia sp., and Hebertella occidentalis, were tested for differences in community structure and distribution using scores derived from Polar Ordination. The sclerobiont communities on R. alternata and Vinlandostrophia sp. show significant differences, and diversity indices show that Vinlandostrophia sp. hosted a less speciose and less diverse assemblage of sclerobionts. Bookstein shape coordinate location data show sclerobionts clustering near the hinge line of H. occidentalis, suggesting that encrustation occurred after the host's death. Sclerobionts on Vinlandostrophia sp. clustered on the sides and avoided the central fold/sulcus, potentially because they were utilizing the lateral inhalant current produced by a living Vinlandostrophia's lophophore. The sclerobionts on R. alternata showed no clustering patterns, but the sclerobiont communities are different between the dorsal and ventral valves of this host. These results demonstrate the importance of host identity and morphology to the structure of sclerobiont communities. Some sclerobiont taxa may have preferred a living host at the time of settlement.