Induction de défense contre l'herbivore Littorina littorea dans l'algue Fucus vesiculosus : influence des stimuli et variation géographique

Induced defense against the herbivore Littorina littorea in the seaweed Fucus vesiculosus: influence of stimuli and geographic variation Grazing by marine herbivores can heavily impact macroalgae, which, in turn, reduce biomass losses through induced resistances. Although this topic has been much studied in recent years, there exists no information on this defense mechanism in the subarctic northwest Atlantic. We tested the macroalga Fucus vesiculosus for inducible resistances by various cues and for plasticity in the response to different grazing pressures. In laboratory, we exposed seaweeds to artificial wounding (clipping) and to two densities of the gastropod Littorina littorea. We assessed whether algae had a decreased palatability every third day for a period of 21 days. Defense was established upon a greater feeding rate of periwinkles on ungrazed/unclipped (control) seaweeds vs. previously manipulated seaweeds in subsequent choice feeding assays. Grazing by the two periwinkle densities caused a trend of resistance of similar intensity while artificial wounding significantly induced defense in seaweeds for 6 consecutive days. While we did not demonstrate a correlation of phlorotannin concentrations with the trend of decreased palatability nor defense flexibility for the two grazing magnitudes, an inducible resistance in a macroalga is established for the first time in the subarctic northwest Atlantic. The few evidences where L. littorea grazing does not trigger a reduced palatability in F. vesiculosus from the northwest Atlantic hint for a geographic variation with the Baltic Sea where it do es stimulate a resistance