ABSTRACT: The consequences of intraspecific variation in prey traits for plant-herbivore interactions were tested by measuring the susceptibility of 3 phenotypes from the red alga Gracilaria cornea against herbivores from the coast of Israel. The 3 algal phenotypes (‘fine’, ‘green’, ‘wild’) differed in morphology, as well as nutritional value (organic content). When presented with the 3 G. cornea phenotypes simultaneously, the amphipod Ampithoe ramondi and the crab Acanthonyx lunulatus consumed significantly more of the finely branched phenotype (63 and 80% of total consumption, respectively) than of either the green or wild phenotypes. When confined with only 1 of the 3 algal phenotypes, feeding patterns of the crab changed little, consuming significantly more of the finely branched phenotype. In contrast, the amphipod responded by increasing consumption proportionally on the phenotypes with the lowest organic content. Regression analysis showed that A. ramondi exhibited compensatory feeding and consumed significantly more of the green phenotype than of either of the other 2 under no-choice conditions, with algal ash-free dry mass explaining approximately 83% of the variance in feeding for this mesograzer. Data suggest that feeding by crabs responded to algal morphology more, while amphipods cued on both structure and nutrient content of the algal phenotypes.