Wounding, healing and survivorship in three kelp species

Pterygophora californica Ruprecht, Eisenja arborea Areschoug and Laminana setchellii Silva are 3 common kelps (Laminariales, Phaeophyta) found in the shallow subtidal of open coastal British Columbia, Canada. Earlier laboratory studies showed that P. californica stipes had a cr~tical flaw length (CFL, the length of a flaw which, if exceeded, results in structural failure) of 0.2 mm. In this paper w e report on studies to determine whether this CFL is valid in situ, whether all 3 species of kelp respond similarly to stipe damage and whether tissue that regrows in the site of a wound increases the mechanical strength of the stipe. We tested the effect of razor cuts less than the CFL and also razor cuts and cuts imposed by a triangular file that exceeded the CFL. Results were not as predicted. Neither razor cuts nor file cuts greater than the CFL significantly decreased the survivorship for P californica over control thalli. L. setchellii had a significantly lower survivorship when cut by a triangular file but not when cut by a razor Tissue regrowth does not significantly increase mean strength of the stipe. We hypothesize that the low survivorship of L. setchellii a s a result of stipe damage is one factor responsible for preventing successful establishment of adults of this species in sites where sea urchins a re common. In contrast, the comparatively h ~ g h e r survivorship of P. calilornica adult plants subjected to similar damage may be one factor enabling this species to survive in such sites.