Marine invertebrate grazers can, depending on their abundances, consume large quantities of biomass within a short period of time and, in many systems, are therefore a major threat for macroalgal populations.
It is known that many seaweed produce secondary metabolites against herbivory and, in this context, it is a widespread notion that the allocation of defensive compounds is costly in terms of metabolic energy. If this is true, the ability to defend should be reduced under conditions of environmental stress.
To asses the effects of low-light stress on macroalgal palatability, we kept individuals of the red seaweed Chondrus yendoi under 6 different light regimes for 10 days and subsequently conducted feeding assays to test for differences in grazer consumption between treatment groups. Additionally, we checked for the presence of an inducible defense in Chondrus yendoi, by adding herbivores to half of the experimental units during the stress induction phase.
Two grazers were here: Lacuna smithii (Gastropoda) and Idotea ochotensis (Isopoda).
A significant effect of light reduction on algal palatability was detected for L. smithii but not for I. ochotensis, while an effect of the grazing history on the defensive status was found as a response to grazing by I. ohotensis but not when L. smithii fed on the seaweed.
From these results, we infer that C. yendoi to grazing is herbivore specific. In case of the slow-moving gastropod it showed a constitutive defence which was clearly affected by previously experienced light intensities, while in case of the highly mobile isopod the defense was induced and, however, not affected by the amount of energy available for the seaweed.
|