Egregia menziesii (O. Laminariales) is an important habitat-structuring component of shallow, benthic communities throughout central and southern California. Morphological variation in this species is high, particularly in the lateral blades that distichously cover the flattened branches. Fertile sporophylls are believed to be produced throughout the year, but to be most abundant between April and November. However, spatial and temporal patterns of thallus morphology and sporophyte reproduction have not been investigated in Southern California. We studied lower intertidal populations of E. menziesii at three southern California sites separated by <16 km. Growing axes (n = 9) were collected monthly to quantify sporophyll production and the frequencies of different types of lateral blades. Band transects were surveyed quarterly to determine temporal patterns of sporophyte recruitment. Sporophylls were found throughout the year, but sporophyll densities showed a strong peak in winter (December) at all three sites. Sporophyte recruitment began in late February and peaked in June, suggesting a gametophyte period of approximately 6 months. Lateral blade morphology at the three sites varied in a consistent pattern and was related to axis length; most thalli initially developed spatulate lateral blades and then produced narrower, filiform laterals. Thalli subjected to intense grazing pressure had shorter axes and were dominated by spatulate blades, while those growing under low grazing pressure exhibited longer branches, densely covered with filiform laterals. Observed changes in the frequencies of morphologically variable lateral blades along E. menziesii axes hypothetically affect productivity, susceptibility to grazing, and thallus drag in this shallow water kelp.

Key words: Egregia menziesii, kelp, morphology, productivity, recruitment, reproduction