IMPACTS OF EGREGIA MENZIESII, A FOUNDATIONAL ALGA, ON INTERTIDAL COMMUNITIES IN SOUTHERN CALIFORNIA AND NORTHERN WASHINGTON

Canopy-forming seaweeds can function as both ecosystem engineers and foundation species in intertidal systems. In this study, I focused on the canopy-forming seaweed Egregia menziesii (feather boa kelp) with two main objectives: 1) compare community structure between areas with and without Egregia and 2) compare community structure before and after Egregia was manipulated in situ. In the intertidal zone in two regions: southern California (Los Angeles County) and northern Washington (San Juan County) I conducted a two-year experiment with three treatments: Natural Egregia (no manipulation), Egregia (Egregia removal), and No Natural Egregia (no manipulation). I surveyed community structure at approximately 6-month intervals and analyzed metrics of community composition and diversity. Community structure differed among treatments and seasons in both regions, but Egregia cover was highly variable over time. During low tide on hot days, temperature and light intensity were lower underneath Egregia canopy than out on unshaded surfaces. At the cover levels used in my study, Egregia did not exert an obvious influence as a foundation species, although it did function as an ecosystem engineer through the amelioration of abiotic stressors. 

One additional component of this study was to test the ability of a commercially available aquarium-grade replica to mimic the effects of natural Egregia individuals in the field. The mimics copied morphological characteristics of natural Egregia but did not ameliorate heat and light stress during low tide to the same degree as natural thalli. Community structure in plots with Egregia mimics was not the same as in plots with Natural Egregia. Overall, the mimics did not provide insight on the mechanisms through which Egregia influences community structure.