Meeting Abstract
Macroalgae attached to wave-swept rocky shores can form canopies that provide habitat and food for many other organisms. Large seaweeds can outcompete neighbors for space and light, but are at greater risk than smaller seaweeds of being damaged or dislodged by hydrodynamic forces, especially in the winter when seasonal storms produce large ocean waves. We used the kelp Egregia menziesii, a dominant canopy-forming intertidal kelp along the California coast, to examine how kelp structure (i.e. total size, number of fronds) changed seasonally and over the lifetime of a kelp, how the kelp structure influenced the presence of epifauna on the kelp, and how the grazing by epifauna influenced the structure of the kelp. Through long-term surveys of E. menziesii populations at several sites in northern California, we found that fronds usually break rather than being totally lost, and that the broken fronds produce new branches. Therefore, these kelp typically become more branched and have more fronds over the course of their lives. E. menziesii with many fronds tend to host more herbivorous epifauna, such as limpets, amphipods, isopods, and kelp crabs. Grazing by these animals can wound fronds, which are likely to break at such injuries. Thus, epifaunal herbivores can facilitate the shortening of fronds, which in turn causes the kelp to become more branched and to thus host more grazers. The shortening of the fronds in the late fall and winter is an important process that helps E. menziesii reduce its overall size and survive winter storms, but maintaining a large number of fronds through winter is also important for ensuring that the kelp can begin the next year ready to compete against neighboring kelp for space and light.
