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Experimental Design: In May 2006, we established 20 permanent plots in the low intertidal zone at each of 13 sites (n = 260 plots), marking the corners of every 25 × 25 cm plot with stainless steel lag screws and a labeled washer. At each site, we selected representative community types for the five replicate blocks, and within each block we applied four treatments: control with no manipulations, recovery with all organisms removed initially but no further manipulations, macrophyte-only with all organisms removed initially and then regular removal of sessile invertebrates, and invertebrate-only with all organisms removed initially and then regular removal of macrophytes. In addition, Hacker et al. 2019 analyzed the results of a fifth treatment, consumer exclusion, which existed from 2006 to 2008. To remove all organisms initially from the non-control treatments, we scraped most species from the rock and then sprayed oven cleaner (NaOH) to kill encrusting species. We removed sessile invertebrates recruiting into the macrophyte-only plots and macrophytes recruiting into the invertebrate-only plots with needle nose pliers, wire brushes, knives, forceps, and pry bars while minimizing damage to the remaining organisms. From 2006 through 2008, removals were conducted monthly from spring to autumn, and as often as feasible during the winter. After the first three years, removals were conducted less frequently, but at least annually.

Hacker, S. D., Menge, B. A., Nielsen, K. J., Chan, F. & Gouhier, T. C. Regional processes are stronger determinants of rocky intertidal community dynamics than local biotic interactions. Ecology 100, e02763 (2019).

Community Surveys: From 2006 through 2020, we surveyed all experimental plots annually during the lowest tides of the spring and summer. We conducted 3,703 of 3,900 possible surveys (95%), with most of the missing data from KH. In our community surveys, we identified organisms to the lowest practical taxonomic rank (except coralline algae, usually species, but occasionally genus) and quantified their abundance in each plot. Abundances of sessile invertebrates, algal crusts, macrophytes, and substrate (bare rock and sand) were measured as percent cover, while mobile invertebrates were counted. Total cover of sessile organisms may be greater than 100 percent because of epibiotic species (e.g., barnacles attaching to mussels) and the layering of canopy macrophytes above understory algae.