Structural resistance of algae to herbivores

Experiments were conducted to determine the forces required for two limpet species to remove tissue from three different types of algae. This was done by using the radulae of the limpets, mimicking the way they use this feeding apparatus. For both Acmaea mitra Rathke (a specialist herbivore) and Notoacmea scutum (Rathke) (a generalist herbivore), Iridaea cordata (Turn.) Bory (a thin, bladed red alga) required the most force; Hedophyllum sessile (C.Ag.) Setch. (a thick, bladed brown alga) the next; and Pseudolithophyllum whidbeyensi (a crustose, calcified alga) required the least amount of force for tissue removal. These results are the inverse of the predictions made by current functional form and functional group models which use the thallus form as a predictor of herbivore resistance. Thallus form alone is a poor predictor of structural resistance to molluscan feeding; the material properties of the alga, the feeding apparatus of the herbivore, and the mode of feeding all must be considered.