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Differences with respect to anti-herbivore defense were investigated in invasive and native populations of the seaweed Gracilaria vermiculophylla. Specimens from 6 native populations in East Asia and from 8 populations invasive in Europe and the Mexican Pacific coast were maintained under identical conditions and offered to herbivorous snails from both the native range (Littorina brevicula) and Europe (L. littorea) in no-choice feeding assays. L. brevicula consumed in total significantly larger amounts of G. vermiculophylla tissue than did L. littorea. Further, both snail species least consumed the seaweed specimens originating from either non-native populations or from populations native to the Korean East Sea/Sea of Japan. The Korean East Sea/Sea of Japan had previously been identified as putative donor region of all the invasive populations of G. vermiculophylla. Thus, populations in the donor region as well as non-native populations in different invaded realms feature an increased capacity to resist feeding pressure. Differences in nutrient content did not account for the observed patterns of consumption, as palatability and carbon to nitrogen (C:N) ratio were not significantly correlated. Thus, mechanical or chemical defenses or the content of feeding cues influenced the behavior of the snails. We suggest that low palatability contributed to the invasion success of the species.

Meso-herbivores can strongly affect biomass accrual and macrophytobenthic commu- nity structure. To counter grazing effects, constitutive and induced anti-herbivory responses evolved in seaweeds. Feeding-assayed induction experiments were conducted in the laboratory to investigate whether 14 d grazing periods by either the periwinkle Littorina brevicula or the abalone Haliotis dis- cus induced anti-herbivory defences in the green alga Ulva pertusa and the brown alga Laminaria japonica. Where appropriate, assays were repeated with artificial food containing lipophilic algal extracts, using dichloromethane (DCM) as a solvent, to test whether or not snails induced chemical defences. While exposure to periwinkles reduced palatability of fresh L. japonica pieces for naive conspecific grazers, no such effect was displayed by abalone-exposed L. japonica pieces. Patterns of grazer specificity in the palatability of fresh algae were not confirmed when using artificial food con- taining algal DCM extracts. This suggests that L. japonica either induced morphological defences or periwinkle-deterrent substances originated from the non-lipophilic fraction of defensive chemicals. Grazer-specific induced responses were not apparent in U. pertusa assays. This study revealed that the induction of chemical anti-herbivory responses depends not only on the type of grazer but also on the type of alga on which the grazer feeds.