Meeting Abstract
In the intertidal zone, structural damage from herbivory, abrasion, and hydrodynamic forces can limit the growth and survivorship of seaweeds. Despite these limitations, the kelp Egregia menziesii is able to grow to large sizes: individual fronds can reach lengths over 6 m and the cumulative length of fronds on a single kelp can exceed 75 m. Herbivory from limpets is known to facilitate frond breakage, reducing the total E. menziesii size and altering its subsequent growth. Smaller individuals are better able to survive stronger currents and larger waves that might otherwise dislodge the kelp, demonstrating a mutualistic relationship between the herbivore and kelp. However, it is unknown how the location of the frond break affects the kelp’s growth, which is especially relevant because herbivores commonly found on E. menziesii occupy and graze different areas along the fronds. To answer this question, I characterized the spatial distribution of herbivores on E. menziesii fronds from intertidal populations in northern California. In early summer, I simulated frond breakage caused by grazing limpets (broken near the holdfast) and amphipods (broken 1 m from the holdfast) on separate sporophytes of similar size. Growth rates of intact fronds and the generation of new fronds were recorded for two months after the initial breakage. Frond breakage location did not affect growth rates of remaining fronds, but sporophytes that experienced amphipod damage produced more new fronds than those with limpet damage.Therefore, different herbivore types can uniquely affect the structure and growth of E. menziesii depending on where they graze. The effects on E. menziesii structure directly translate to the kelp’s ability to form habitat for smaller organisms, and the magnitude of this effect can change with the local herbivore species composition as well as the nutrient and thermal properties of the ambient seawater.
