Prey defense, predator preference, and nonrandom diet: the interactions between Pycnopodia helianthoides and two species of sea urchins

Moitoza, DJ.; Phillips, DW.

Marine Biology (Berlin) 534: 299-304

1979


ISSN/ISBN: 0025-3162
DOI: 10.1007/bf00391611
Accession: 021597291

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Abstract
Interactions between the predatory sea star P. helianthoides (Brandt, 1835) and 2 of its natural prey, the sea urchins Strongylocentrotus purpuratus (Stimpson, 1857) and S. franciscanus (Agassiz, 1863), are examined with regard to predator preference, predator diet and prey defenses. The sea star can detect both species of sea urchin upstream in a Y-trough, but does not consistently choose one over the other (i.e., no preference). When the sea star is presented with equal numbers of similar-sized specimens of the 2 spp. of sea urchin, its diet is markedly nonrandom; S. purpuratus is eaten almost 98% of the time. The defensive responses of the 2 spp. of sea urchin differ in form and effectiveness. S. franciscanus employs its long spines as defensive weapons, pinching the rays of an attacking sea star. This defensive response is more effective than the pedicellarial response used by S. purpuratus. The nonrandom diet of the predator seems to be due primarily to prey defensive responses that differ in effectiveness, rather than to an intrinsic, behavioral preference of the predator at an earlier stage in the predator/prey interaction.

Prey defense, predator preference, and nonrandom diet: the interactions between Pycnopodia helianthoides and two species of sea urchins