| Although non-indigenous species (NIS) of seaweeds are established in coastal habitats worldwide, the ecological effects of only 6.5 % of seaweed introductions have been studied. In particular, little is known about the feeding responses of native consumers when they encounter new additions to the flora. Yet, native consumers can feed on non-native seaweeds at rates that may determine their success in a recipient community. Both the selective consumption (Biotic Resistance Hypothesis; BRH) and avoidance (Enemy Release Hypothesis; ERH) of NIS of seaweeds by native consumers have been reported. To investigate feeding interactions between native macroinvertebrates and native and non-native seaweeds in southern California coastal waters, I performed a series of two-choice laboratory feeding experiments. Feeding choices of the sea hare Aplysia californica, the snail Chlorostoma aureotincta, the crab Pachygrapsus crassipes, and the urchin Strongylocentrotus purpuratus were determined for four morphologically and/or taxonomically similar pairs of native ( Macrocystis pyrifera, Sargassum agardhianum, Chondracanthus canaliculatus ) and non-native (Undaria pinnatifida, Sargassum horneri, Sargassum muticum, Caulacanthus ustulatus) seaweeds. Native macroinvertebrates consumed native over non-native seaweeds in seven experiments, consumed non-native over native seaweeds in three experiments, and made no choice in the remaining six experiments. The feeding choices of southern California macroinvertebrates for native or non-native seaweeds do not consistently follow predictions of either the ERH or the BRH, indicating that the feeding responses and potential impacts of native consumers on a seaweed introduction must be evaluated on a case-by-case basis. |
