Meeting Abstract
Kelp are ecologically-important organisms in wave-swept coastal areas where they provide food and habitat for many other organisms. Previous studies have shown that wounds from herbivory can facilitate the breakage of kelp by waves and currents. We used the long, flexible kelp, Egregia menziesii, to study how herbivore wounds affect breakability of kelp fronds, how wounds interact with the twisting of fronds by waves to affect breakage, and how wound healing affects tissue mechanical properties as well as new frond growth after wounding. We found that the structure of E. menziesii fronds is fairly robust against the wounds caused by its most common amphipod herbivore: a hole that removed about 50% of the cross-sectional area of a frond only reduced the tensile breaking load by approximately 30%. The kelp also showed some ability to heal from wounds by strengthening the remaining tissue around a hole. Furthermore, new frond growth at the intercalary meristem was affected by herbivore damage. The supporting rachis of the new portion of the frond that grew after damage was thicker compared with rachis produced pre-damage, but the strength of the new tissue was not different. Twisting had no effect on the mechanics of intact frond tissue, despite our prediction that twisting would pre-stress the frond and cause breakage under weaker forces. However, twisting increased the breaking strength of wounded fronds, suggesting that wounded fronds can survive greater hydrodynamic forces if they become twisted by the ambient water flow. Our results reveal how the structure of E. menziesii fronds allows the kelp to survive in an environment with large hydrodynamic forces and strong grazing pressure, and that herbivores can have a big influence on the interaction of kelp with the surrounding fluid environment.
