FEEDING BIOLOGY OF THE AEOLID NUDIBRANCH FLABELLINA VERRUCOSA

The aeolid nudibranch Flabellina verrucosa is a generalist predator found in the Gulf of Maine. There have been many field and lab observations documenting its association with a number of hydroids, ascidians, and schyphomedusans, but little else is known about their prey preferences or feeding biology. This study investigated the prey preferences of F. verrucosa as well as the potential for ingestive conditioning in this species. Histology of the digestive system of F. verrucosa was also examined and described. Results of both short and long-term preference trials indicated that Flabellina verrucosa has a preference for Ectopleura larynx but this preference seems to be dependent on the density of this hydroid. Decreased abundances of E. larynx motivated F. verrucosa to switch to the next most preferred prey species, which were the hydroid Sarsia tubulosa and the schyphomedusan Aurelia aurita. Ingestive conditioning trials which included S. tubulosa and Obelia geniculata, did not indicate that F. verrucosa was significantly conditioned on either species, though F. verrucosa fed S. tubulosa seemed to be more susceptible to a conditioning effect than slugs fed O. geniculata. These results suggest that innate preferences or densities of prey items may impact prey choice in F. verrucosa more than past experiences with prey. The digestive system of Flabellina verrucosa was described and many adaptations were found that assist the animal in maintaining a generalist diet. A cuticle throughout the buccal cavity and esophagus, oral and saliva glands in the buccal complex, and numerous vacuoles in the epithelial cells of the stomach and digestive gland were found and all appear to be adaptations to reduce damage from nematocysts as they make their way through the digestive tract. Numerous folds in the wall of the buccal cavity, esophagus, and stomach were found, presumably to function in expanding these structures to take in as much prey as possible. Both types of adaptations may assist F. verrucosa in maintaining a wide diet. The ability to prey switch is especially beneficial for survival of this aeolid species, as the fouling communities in which it is found in the Gulf of Maine are highly susceptible to dramatic population shifts