Ephemeral macroalgae display spatial variation in relative palatability

Although geographic variation in algal–herbivore interactions should be common, our appreciation of such variation remains incomplete. For example, feeding choice assays examining variation in palatability of algae typically compare multiple algal species or genera from a single location or a single alga from multiple locations. Unfortunately, most studies have not compared the interaction of herbivores with multiple algae from multiple locations, thus tests of variation of relative palatability are lacking. To examine spatial variation in algal palatability we determined the feeding preferences of the periwinkle snail Littorina littorea when offered multiple algal genera at the same time from two regions in choice assays. Multi-choice experiments were repeated throughout the year to examine temporal variation in feeding preferences. Consistent with previous studies, L. littorea preferred to feed on ephemeral algae compared to perennial species. Importantly, the relative palatability of the two ephemeral genera, Ulva and Porphyra, varied greatly between regions and seasons. Under certain conditions, Ulva only represented 24% of consumed algal wet mass in choice assays, while under other conditions, Ulva was eaten almost exclusively. Preferences for Ulva or Porphyra were unrelated to differences in morphology. Variation in the relative palatability of algae could influence consumer behavior leading to shifts in algal communities across broad geographic scales.

► Herbivore preference for two ephemeral algae switched depending upon algal source.
► Snail feeding preferences were unrelated to differences in algal morphology.
► Herbivore feeding preference displayed temporal variation.