The palatability of two solitary and three colonial species of ascidians commonly found in sub-tropical
seagrass meadows was evaluated using the abundant, sympatric, omnivorous pinfish Lagodon rhomboides as a
model predator. Bite-sized pieces of fresh tissues of both solitary and one of the three colonial ascidian species
were unpalatable to fish. Lipophilic and hydrophilic extracts of the three unpalatable species did not cause
feeding deterrence indicating that secondary metabolites are not responsible for the lack of palatability.
Distaplia bermudensis, the one colonial ascidian that was unpalatable to fish, had a highly acidified outer tunic
(pH=1.5). We tested the ability of acidified agar food pellets (pH=1.5) to deter pinfish and found that the
fish readily ingested acidified pellets. The toughness of the tunic of all five ascidian species was evaluated by
measuring the Force (N) required to penetrate the tunic using a penetrometer. Tunic toughness is likely to
explain the lack of palatability of the solitary ascidians Styela plicata and Molgula occidentalis as their tunics
required a force of N34 N to penetrate. Tunic toughness may be a particularly effective adaptation for ascidian
defense in seagrass habitats where fish with strong crushing jaws, such as those that commonly occur in coral
reef systems, are rare.