Reconstructing predation intensity on crinoids using longitudinal and cross-sectional approaches

Abstract

Predation has been hypothesized as important to crinoid ecology, and numerous crinoid traits have been linked to predation. However, testing such hypotheses requires some assessment of predation intensity, or pressure. Although direct observations of predatory activity on crinoids are exceedingly rare in the Recent, and unobservable in the fossil record, evidence of predation exists in the form of sublethal damage, especially to their arms. Substantial data exist on the relative frequency, or prevalence, of such injuries, but estimating predation intensity in taxa with ephemeral injuries, such as crinoids, requires combining the prevalence of injuries with rates at which they heal (regenerate). An alternate, independent estimate of predation intensity involves gathering longitudinal data on the number of injuries incurred by particular individuals over a given time span. In this study, predation intensity on crinoids is explored experimentally using these two approaches. We demonstrate that for the two feather star species examined, Capillaster multiradiatus and Clarkcomanthus mirabilis, both methods produce reasonably consistent results and that predation intensity is slightly lower on the latter perhaps because it responds to tactile stimulation by crawling deeper into its perch, whereas the former shows no response.