Predation on juvenile Aplysia parvula and other small anaspidean, ascoglossan, and nudibranch gastropods by pycnogonids

This study investigates the predation on opisthobranchs by the pycnogonid A noplodactylus evansi. Anoplodactylus evansi attached and fed on small indiv iduals of 13 different species of anaspidean, ascoglossan (sacoglossan), an d nudibranch gastropods in this study. This predator was used to investigat e the feeding deterrent effects of diet-derived compounds in the sea hare A plysia parvula. Anoplodactylus evansi was not deterred from feeding on A. p arvula containing diet-derived secondary metabolites from the red seaweeds Laurencia obtusa or Delisea pulchra. However, increasing the quantity of me tabolites present in A. parvula by treatment with adult extracts did deter A. evansi from feeding, suggesting that high levels of diet-derived materia ls in sea hares may have deterrent effects against a predator. A. evansi do es not appear to sequester algal secondary metabolites from its prey. The a bundance of A. evansi and A. parvula on the alga L. obtusa was measured to determine if this pycnogonid influences the population of sea hares in the held. A. parvula occurred in significantly lower abundance on L. obtusa L. thalli inhabited by A. evansi over consecutive years, a pattern consistent with population-level effects by this predator.