Experimental and theoretical investigations of filter feeding mechanisms of recent and fossil crinoids
Final Report Abstract
Recent stalked crinoids live primarily in the deep sea and access to their remote habitat is very limited. First representatives are known from the Ordovician, and were very abundant during several time intervals of the Palaeozoic and Mesozoic era. Crinoid feeding has generated high interest during the last decades, and the knowledge derived from typical living forms was used for interpretation of their fossil representatives. These studies, however, focussed on stalked crinoids that possibly used the parabolic filtration fan for feeding, while investigations of forms that differ in their morphology and thus probably used a different feeding position are scarce. While general particle capture mechanisms of passive suspension feeders have been studied in detail, the global flow pattern around crinoids, especially of those differing in morphology, has been neglected widely. For the reconstruction of palaeoenvironments, however, as well as for conclusions concerning particle encounter, the feeding position and thus ambient flow regime is of high importance and was thus the focus of the presented project. This study complements the current knowledge on particle capture mechanisms involved in crinoid feeding and provides insights into global flow patterns that form around different filter apparatuses of recent and fossil crinoids. For the parabolic filtration fan, which is adopted by living stalked crinoids, no global recirculation could be detected that is involved in feeding. Local small scale eddies do not transport particles so that plankton is utilized by direct capture out of the through-flowing water. The fossil morphology that forms a tear shape, in contrast, evokes a recirculation zone directly behind and inside the filter. Here, the eddies contribute considerably to particle transport onto the oral surface, when the inflow came from the aboral side. While the parabolic filtration fan is adapted to unidirectional inflow with moderate inflow velocities coming from the aboral side, the fossil morphology proved to be suitable for feeding in different flow directions. With an aboral inflow, particle capture by recirculation currents was the dominant mechanism. Due to the tear shape, higher inflow velocities could be tolerated. Injury by predation or autotomy resulted in considerable decrease in the number of plankton particles that actually reached the filtering surface, even if the recirculation current with aboral inflow still developed. With flow coming from the lateral or oral side, direct capture of plankton particles was possible. Here, lower flow velocities were advantageous so that the pressure acting on the filtering surface remained in a tolerable range. By variation of arm and pinnule posture, the crinoid could respond actively to changes in flow conditions. E. liliiformis thus was able to feed in dynamic environments typical for shallow water habitats by adopting a feeding position differing from living representatives.
Publications
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2015: Echinoderms: Hierarchically organized light weight skeletons. In: Hamm, C. (ed.): Evolution of Lightweight Structures: Analyses and Technical Applications, Biologically-Inspired Systems, Vol. 6, Springer Verlag. 141-156. ISBN-10: 9401793972
Nebelsick, J.H., Dynowski, J.F., Grossmann, J.N. & Tötzke, C.
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2015: Hydrodynamic analysis of suspension feeding in recent and fossil crinoids. PhD Thesis, Eberhard Karls Universität Tübingen
Dynowski J. F.
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Computational Fluid Dynamics Analysis of the fossil crinoid Encrinus liliiformis (Echinodermata: Crinoidea). PLoS ONE 11(5): e0156408, 2016
Dynowski, J. F., Nebelsick, J. H., Klein, A. and Roth-Nebelsick, A.
