Charles Messing's Crinoid Pages: Predation On Crinoids

Meyer and Ausich (1983) and Meyer (1985) characterized predation on living feather stars as chiefly sublethal grazing by non-specialist fishes with damage including missing and regenerating arms, pinnules and visceral masses. They listed nine fish families including known feather star predators: Lutjanidae, Ephippidae, Chaetodontidae, Labridae, Monacanthidae, Tetraodontidae, Notacanthidae, Balistidae and Sparidae. Meyer (1985) noted that the triggerfish Balistoides conspicillum was the best documented, but only the sparid Chrysophrys auratus was known at the time to feed on numbers of whole feather stars. An orange-striped triggerfish (Balistapus undulatus) was photographed feeding on a crinoid in 2009. Meyer pointed out that sublethal predation pressure on tropical reef-dwelling crinoids appears to be relatively low; 47% of specimens had one or more missing or regenerating arms (chiefly <5). Semicryptic and cryptic species suffer less damage than species that perch in the open (Meyer 1985, Schneider 1988). However, Mladenov (1983) reported that 80% of Florometra serratissima specimens off Vancouver Island had one or more regenerating arms. He attributed the arm loss to the crab Oregonia gracilis and the asteroid Pycnopodia helianthioides. At least some attacks by fish may be directed at the numerous commensals and parasites resident among crinoid arms (Meyer 1984 1985). Behavioral, morphological and visual camouflage by some of these commensals suggests that they represent a potential food source and that their hosts provide significant shelter.

Since then, predation has been recorded on sea lilies as well. Bowden et al. (2011) observed the sea star Porania antarctica and the sea urchin Sterechinus antarcticus feeding on Ptilocrinus amezianeae, and several papers have discussed predation by pencil urchins (Cidaridae) on Endoxocrinus parrae and Neocrinus decorus (see also under Locomotion on this website), and the implications for crinoid evolution (Oji 1996, Baumiller 2008, Baumiller et al. 2008, 2010).

Possible defenses against predation include incorporation of distasteful or toxic compounds; for feather stars: hiding completely during the day (most bony fishes that feed on calcareous prey are day-active), and protecting the visceral mass via semicryptic behavior, large spine-like oral pinnules, or a dense thicket of arms and pinnules (Rideout et al. 1979, Bakus 1981, Meyer & Ausich 1983, Meyer 1985). Feather stars and some sea lilies can crawl to escape predators, and some feather stars can swim (See under Locomotion on this website). Oji and Okamoto (1994) demonstrated how the branching pattern of rays and the distribution of autotomy points (syzygies) in shallow-water feather stars (typified by Anneisia japonica) approach a theoretically ideal pattern that minimizes the effects of arm loss via predation. They contrasted this with a pattern found in deep-water isocrinids (e.g., Metacrinus rotundus) that approaches an arrangement ideal for harvesting food in a low-predation environment.

In addition, feather stars display substantial regenerative powers. Meyer (1988) reported that the visceral mass of tropical Himerometra robustipinna may regenerate completely within three weeks of evisceration. Cold temperate Florometra serratissima completely regenerates 200-mm-long arms in 9 months (Mladenov, 1983). Crinoids thus exhibit a suite of features that ostensibly confer a measure of protection against predation and that apparently have contributed to their success in shallow-water following the late Mesozoic radiation of durophagous predators (those that can feed on hard-shelled prey) (Meyer & Macurda 1977, Meyer 1985, Schneider 1988, Oji & Okamoto 1994, Oji 1996, Messing 1997, Baumiller et al. 2010).

Note, however, that one or more clusters of regenerating arms may be due to “adolescent” autotomy, in which species that have more than ten arms when fully developed purposefully drop an arm or group of arms at a ligamentary articulation (syzygy or synostosis) at an arm base or in a brachitaxis to increase their arm number via regeneration.

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