Within-alga integration and compensation:: Effects of simulated herbivory on growth and reproduction of the brown alga, Fucus vesiculosus

We investigated the level of within-alga integration, the consequent ability to compensate for simulated herbivory, and the effect of nutrient availability on the ability to compensate in Fucus vesiculosus (L.). Although F. vesiculosus lacks vascular connections, resource translocation occurs on a local scale. Vegetative apical parts and reproductive structures were dependent on the resources provided by the mature thallus. Thus, damage from herbivory has the potential to decrease the growth and reproductive success of F. vesiculosus. In contrast to vascular plants, F. vesiculosus did not show any plasticity in response to different types of damage. Removal of an apical part terminated the growth of the focal branch but had no effect on the growth of the neighboring branch. Removal of the older part of the thallus had no effect on the branching of the apical meristems. Thus, the within-alga growth pattern remained similar whether the old thallus or an apical part was damaged. Increased resource availability did not enhance the ability of algae to compensate for lost thallus. The strong dependence of the apical part on the older thallus and the low plasticity in the type of response to damage indicate that in F. vesiculosus the tolerance of herbivory may be low.