Prey preferences of the polyclad flatworm Prostheceraeus roseus among Mediterranean species of the ascidian genus Pycnoclavella

In the present study we analyzed prey preferences of the polyclad flatworm Prostheceraeus roseus among three different species of colonial ascidians of the genus Pycnoclavella occurring sympatrically in the Northwestern Mediterranean (Spain). Palatability assays were conducted in laboratory conditions in order to test predator preferences in pairwise tests, and cycles of abundance of the predator and prey were monitored in the field. The results showed a clear preference of the predator for Pycnoclavella communis over Pycnoclavella nana and Pycnoclavella aurilucens. We suggest that chemical variation in defense compounds among species of this secondary metabolite-rich genus can drive the flatworm preferences. The ascidian had seasonal cycles in the area studied, with resting (aestivation) states in the summer months. The flatworm abundance showed no clear seasonal cycle, but it was less abundant in winter. The predator has been seen in the field feeding either on active zooids or on the reserve-laden basal mass of tunic during the aestivation phase of P. communis. Handling editor: I. Nagelkerken