Seaweed-herbivore-predator interactions: host-plant specialization reduces predation on small herbivores

摘要: Because feeding specialization among marine herbivores is rare, communities provide a simplified system for identifying factors selecting specialization. On Australia's Great Barrier Reef, we investigated interactions the chemically-defended seaweed Chlorodesmis fastigiata, specialized on this alga, and potential predators of these herbivores. low preference food reef fishes but appears to be only crab Caphyra rotundifrons ascoglossan gastropods Elysia sp. Cyerce nigricans. The found in patches Chlorodesmis, feeds solely selectively shelters it laboratory choice experiments. Crab grazing red Acanthophora spicifera was stimulated when alga coated with increasing concentrations cytotoxic diterpenoid chlorodesmin, major secondary metabolite Chlorodesmis. Crabs did not sequester metabolites avoided by sheltering unpalatable alga. All crabs tethered without access were rapidly eaten; those much less susceptible predation. cryptic exclusively sequestered from Living common wrasse Thalassoma lunare assays, crude organic extract significantly deter Thalassoma. which deterred field assays ineffective against at 5% dry mass. Unlike Elysia, aposematically colored nigricans relatively small amounts, produced larger amounts unrelated polypropionate compounds. never attacked slug strongly wrasses assays. dorid nudibranch Gymnodoris appeared predator Elysia; would prey Cyerce. Data other recent investigations demonstrate that some feed or seaweeds are chemically defended fishes. This association reduces predation suggests escape deterrence may dominant factor