INDUCTION AND REDUCTION OF ANTI‐HERBIVORE DEFENSES IN BROWN AND RED MACROALGAE OFF THE KENYAN COAST1

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Abstract
Herbivory is particularly intense in tropical benthic communities, suggesting preference of constitutive, rather than inducible, anti‐herbivory defense. The objective of the study was to examine whether anti‐herbivore defenses in the red algaHypnea pannosaJ. Agardh and the brown algaeSargassum asperifoliumHering and G. Martens ex J. Agardh andCystoseira myrica(S.G. Gmelin) C. Agardh could be induced and subsequently reduced in response to grazing by the amphipodCymadusa filosaSavigny. During a 14‐day treatment phase, algae were exposed to amphipod grazing or were left ungrazed (control). Subsequently, one subset of algae was used in feeding assays, whereas another was cultivated for additional 14 days without consumers (recovery phase). At the end of each phase, bioassays were conducted to detect defensive traits in terms of differences in consumption rates of grazed and control pieces of live algae and agar‐based food containing nonpolar algal extracts. Consumption of grazed liveS. asperifoliumandH. pannosaspecimens was lower than of control algae. Furthermore, nonpolar extracts of grazedS. asperifoliumandC. myricawere less preferred than those from control algae. Defensive responses were exclusively detected after the treatment phase, although strong preference of ungrazedH.pannosaandC.myricaover grazed conspecifics continued throughout the recovery phase. These findings suggest that phenotypic plasticity in anti‐herbivory defense of marine macroalgae 1) might be more common than previously shown, 2) could be switched on and off within 2 weeks, and 3) can be found in nonpolar algal extracts.

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