Induction of anti-herbivore defences by direct amphipod consumption and water borne grazer cues in macroalgae

Dissertação mest., Estudos Marinhos e Costeiros, Universidade do Algarve, 2007

Serrão, Ester

Herbivores have been repeatedly shown to induce defences in terrestrial plants, but few examples exist from marine macroalgae. In two bio-assayed laboratory experiments we tested the effects of (1) direct amphipod consumption, (2) water borne cues from nearby grazed conspecifics, and (3) water-borne cues from non grazing consumers on the induction of anti-herbivore defences in macroalgae of the southern coast of Portugal. Both the brown alga Fucus vesiculosus and the red alga Sphaerococcus coronopifolius displayed distinct defence regulation. They induced defences when consumers were present and reduced defences again when consumption ceased. A reduction in palatability was considered to be indicative of an alga’s defence mechanism. Defence regulation reacted to consumption stimuli in less than two weeks. For F. vesiculosus we found the defence activity in the lipophilic fraction of the alga’s chemistry. Both algal species induce defences after receiving water-borne signals from nearby grazed conspecifics as well as non-grazing amphipods. These results imply that species of red and brown algae can recognise a suite of cues indicating herbivore pressure, allowing them to adjust their defensive traits in finely tuned short-term responses. Inducible defences may be more common in macroalgae than suspected.