Colonization of rugose corals by diverse epibionts: dominance and syn vivo encrustation in a Middle Devonian (Givetian) soft-bottom habitat of the Holy Cross Mountains, Poland

Middle Devonian (Givetian) rugose corals from the Holy Cross Mountains (Miłoszów), Poland, have been analysed with respect to epibiont colonization patterns. Solitary microconchid tubeworms and colonial bryozoans, hederelloids and ascodictyids numerically dominate on the coral hosts. Moreover, the same taxonomic groups of epibionts dominate both the larger (Heliophyllum, Acanthophyllum, Stringophyllum, Ceratophyllum, Cystiphylloides) and smaller (Thamnophyllum) corallites, indicating the true pattern of epibiosis was achieved. The presence of common bioclaustrated epibionts, constricted and rejuvenated coral calyces, as well as epibionts growing concordantly with the host's growth direction, indicate that at least some corals were colonized during life. The observed low number of overgrowth cases of various epibionts on coral hosts suggests, that competition for hard substrate was negligible, most probably due to abundant coral substrates on muddy sea-bottom of the Givetian sea at Miłoszów. This epibiont community is similar to other known Devonian encrusting communities which likely developed in a more nutrient-rich palaeoenvironments and differs markedly from taxonomically-poor assemblages developing in a more oligotrophic conditions. The presence of Rothpletzella encruster, which is considered to be related to green algae, indicates that the Miłoszów coral community dwelled within the limits of the photic zone.