Water-borne defense induction of a rockweed in the wild

1. Laboratory-scale studies suggest that water-borne chemical cues released in grazing of marine macroalgae act as info-chemicals allowing the yet-undamaged conspecifics to increase their resistance before the actual herbivore attack. The relevance of this finding in natural populations has thus far remained unexplored. 2. We investigated spread of water-borne herbivore resistance in a field experiment using the littoral foundation species Fucus vesiculosus. We exposed algal genotypes for water-borne cues in the distances of 0.5 and 2 meters from the grazed cue-emitting genotypes. We measured herbivore resistance with preference experiments and recorded changes in the phlorotannin content. We recorded changes in biomass and length of the genotypes to test if water-borne resistance correlates with the grazing damage on the cue-emitter or incurs costs for the genotypes in terms of reduced growth. 3. In two of our four experimental blocks, induced resistance via water-borne cues took pla...