COMMENSALISM IN THE MIDST OF EXTINCTION: ENCRUSTERS AND BORERS OF THE APPALACIAN FORELAND BASIN ACROSS THE FRASNIAN-FAMENNIAN BOUNDARY

Ecosystem engineers exert disproportionate control over the taxa for which they create habitat; however, the degree of control ecosystem engineers have on diversity and abundance within their ecological communities on long timescales is not well understood, particularly in cases where they provide attachment substrate for their commensal organisms. Brachiopods and the animals that attach to or bore into their shells (skeletobionts) provide a useful system in which to observe commensal interaction over long timescales because brachiopod shells readily preserve as fossils and often exhibit evidence of boring or encrusting organisms. By examining communities of brachiopods and their skeletobionts through extreme ecological shifts, such as mass extinctions events, we can investigate and potentially quantify the effects of changes in ecosystem engineer populations on their commensals. I examined a series of brachiopod assemblages from multiple sites in western New York State and northern Pennsylvania that represent continental shelf deposits of the Appalachian Foreland basin across the Frasnian-Famennian boundary, including two pulses of the Late Devonian mass extinction. The brachiopods in these assemblages are largely preserved as molds as are many of their borers and encrusters. At least 7 major groups of skeletobiont are present including microconchids, stenolemate and ctenostome bryozoans, hederellids, and various borings that may be attributable to sponges. Preliminary analysis indicates no significant difference between the rates of colonization before, after, or between extinction pulses possibly indicating that the skeletobionts were no more susceptible to environmental variation than their brachiopod hosts. Additionally, two types of shell borings were significantly more likely to be found on particular groups of brachiopod, possibly indicating preferential settling behavior of the boring-maker.