Seawater Temperature Alters Feeding Discrimination by Cold-Temperate but not Subtropical Individuals of an Ectothermic Herbivore

Abstract

Seawater temperature varies across multiple spatial and temporal scales, yet the roles that such variation play in altering biotic interactions are poorly known. We assessed temperature-mediated feeding behavior exhibited by the herbivorous amphipod Ampithoe longimana collected from cold-temperate and subtropical estuaries (27 degrees N and 41 degrees N, respectively). Individuals were offered a pairwise feeding choice between lyophilized seaweeds that provide higher fitness (Ulva intestinalis) or lower fitness (Halimeda tuna, H. opuntia, Amphiroa spp., or Stypopodium zonale). Overall, herbivores preferentially consumed the higher quality U. intestinalis more than any lower quality food. However, the strength of this feeding choice was not consistent. Northern herbivores consumed proportionally more poorer quality tissue at 25 degrees C than at 20 degrees C in two assays (H. opuntia and Amphiroa sp.), consumed less poorer quality tissue at 25 degrees C than at 20 degrees C in one assay (S. zonale), and showed no difference in another assay (H. tuna). Moreover, when offered tissue coated with lipophilic extracts of H. opuntia, northern herbivores consumed more extract-coated tissue at 25 degrees C than at 20 degrees C. In contrast to northern herbivores, the southern herbivores did not alter their feeding choices with temperature. This study represents the first demonstration that short-term (i.e., days-long) variation in ambient temperature alters feeding choices in a marine herbivore.