Reproduction and morphological variation in southern California populations of the lower intertidal kelp Egregia menziesii (O. Laminariales)

Intertidal Egregia menziesii populations were studied at three southern California sites to determine temporal and spatial patterns of reproduction and morphology. The timing of sporophyll production and sporophyte recruitment was similar at all sites. Sporophyll production was much greater during winter periods of colder seawater temperatures and shorter daylengths. Sporophyte recruitment occurred from spring through mid-summer, approximately 5 months following maximal sporophyll production. Lateral blade morphologies varied in a consistent manner suggesting a developmental mechanism for form variation in Egregia thalli. Spatulate blades dominated shorter axes and the bases of longer axes whereas filiform laterals became abundant towards the tips of longer axes. Kelp snails consumed spatulate laterals in greater amounts than filiform laterals but urchins consumed both lateral types at similar rates. Filiform laterals (9.8 mg O₂ g−1 h−1) had higher light-saturated, net photosynthetic rates than spatulate laterals (6.8 Mg O₂ g−1 h−1), resulting in a 12% increase in the productivity of Egregia per meter of filiform frond.