Grazing damage and encrustation by an invasive bryozoan reduce the ability of kelps to withstand breakage by waves

► Bryozoan encrustation and grazing by snails damage kelp blades. ► We examine the effect of this damage on blade material properties. ► Encrustation and grazing lower the strength, extensibility, and toughness of blades. ► Strength reductions occur through the removal or degradation of outer cell layers.