RELATIONSHIPS AMONG PLANT CALCIFICATION, PLANT FORM AND HERBIVORE MODE OF FEEDING IN MARINE PLANT-HERBIVORE INTERACTIONS

Mechanical tests were made of models that predict that algal form and calcification act primarily as structural defenses of marine algae by reducing algal susceptibility to herbivores. The mechanical resistance of a variety of marine algae (tropical and temperate) to herbivores of two important feeding types, rasping herbivores (docoglossan limpets) and a biting herbivore (an herbivorous crab), was measured. In all cases the results did not support the predictions of the models.;I suggest that another factor, the probability of subsequent tissue loss due to herbivore damage, may play an important role in the impact of herbivores on the algae they consume. For some algal species, secondary tissue loss may greatly exceed primary loss to herbivores. Calcification and other potential "structural defenses" such as thallus form may play a more important role in minimizing this secondary tissue loss than in preventing herbivores from removing tissue as has been suggested in the past.