RESEARCH ARTICLE Reestablishment of the Southern California Rocky Intertidal Brown Alga, Silvetia compressa : An Experimental Investigation of Techniques and Abiotic and Biotic Factors That Affect Restoration Success Stephen G. Whitaker, 1,2 Jayson R. Smith, 1,3 and Steven N. Murray 1 Abstract Previous research has indicated that many rocky inter- tidal macrophyte communities in southern California, and other locations around the world, have shifted from larger, highly productive, fleshy seaweeds toward a smaller, less productive, disturbance-tolerant flora. In widespread decline are ecologically important, canopy-forming, brown seaweeds, such as the southern California rockweed species Silvetia compressa. Restoration efforts are common for depleted biogenic species in other habitats, but restoration within rocky intertidal zones, particularly on wave-exposed coasts, has been largely unexplored. In two phases, we attempted to restore Silvetia populations on a southern California shore by transplanting live plants and exper- imentally investigating factors that affect their survival. In Phase I, we implemented a three-way factorial design where juvenile Silvetia thalli were transplanted at four sites with a combination of simulated canopy and herbi- vore exclusion treatments. Transplant survival was low, although enhanced by the presence of a canopy; site and herbivore presence did not affect survival. In Phase II, we used a two-way factorial design, transplanting two size classes of rockweeds (juveniles and reproductive adults) on horizontal and partially shaded, north-facing vertical sur- faces at a target location where this rockweed has been missing since at least the 1970s. Transplant survival was moderate but lower than natural survival rates. Larger thalli exhibited significantly higher survival rates than smaller thalli in both the transplanted and naturally occur- ring populations, particularly on vertical surfaces. Higher mortality on horizontal surfaces may have been due to dif- ferences in desiccation stress and human trampling. Trans- planting reproductive adults resulted in the subsequent recruitment of new individuals. Key words: brown algae decline, canopy-forming algae, coastal ecology, rockweeds, seaweed restoration. Introduction Reestablishing or enhancing depleted biogenic populations are common strategies to restore abundances and ecosystem func- tioning in anthropogenically disturbed habitats. Restoration efforts are common in terrestrial (Larissa et al. 2006), estuar- ine (Orth et al. 1994; Zedler 1996), freshwater (Friberg et al. 2006), and, to a lesser degree, coastal marine ecosystems (Pur- java & Remesh 1993; Hernandez-Carmona et al. 2000). With the exception of surfgrass (Holbrook et al. 2002; Bull et al. 2004) and the brown algae Fucus (Stekoll & Deysher 1996), Lessonia (Correa et al. 2006), and Cystoseira (Susini et al. 2007), restoration efforts on rocky intertidal shores, especially 1 Department of Biological Science; California State University, Fullerton, PO Box 6850, Fullerton, CA 92834-6850, U.S.A. 2 Present address: National Park Service, Channel Islands National Park, 1901 Spinnaker, Ventura, CA 93001, U.S.A. 3 Address correspondence to: J. R. Smith, email jasmith@fullerton.edu © 2010 Society for Ecological Restoration International doi: 10.1111/j.1526-100X.2010.00717.x on wave-exposed coasts, have been largely unexplored. Given the widespread changes in flora and fauna on many rocky shores (Thompson et al. 2002), restoration efforts in these habitats are ripe for exploration. Although efforts to restore other systems have expanded our knowledge, the lack of work conducted in rocky intertidal systems highlights the need to better understand methodologies and factors that affect restora- tion success (Holbrook et al. 2002; Correa et al. 2006; Susini et al. 2007). Anthropogenically induced perturbations to rocky intertidal ecosystems are evident worldwide. These have been linked to declines in large conspicuous invertebrates (Miller & Lawrenz- Miller 1993; Thompson et al. 2002), seagrasses (Short & Wyllie-Echeverria 1996), and fleshy macroalgae (Bokn & Lein 1978; Vogt & Schramm 1991; Rodriguez-Prieto & Polo 1996), as well as shifts toward seaweed communities dominated by disturbance-tolerant turfs (Benedetti-Cecchi et al. 2001). Declines in biogenically important fleshy seaweeds have often been attributed to nutrient pollution (Bokn & Lein 1978; Vogt & Schramm 1991; Rodriguez-Prieto & Polo 18 Restoration Ecology Vol. 18, No. S1, pp. 18–26 SEPTEMBER 2010