Data Compilation
We searched the ISI Web of Science database (26 October 2017) and ProQuest Dissertation & Theses database (25 November 2017) to find studies of the effects of turf algae on canopy algal species (see Appendix S1 in Supporting Information for a list of search terms). These searches resulted in 1,916 unique manuscripts. Of these results, studies were included if they met the following inclusion criteria:
A list of the total papers assessed, and whether each was included, can be found in Appendix S1 Table S1. We supplemented these records with additional studies that met our inclusion criteria, obtained via personal communication and literature cited sections of papers. This resulted in included studies from 41 manuscripts (some manuscripts included multiple studies with unique response variables or treatment types). For each study, we recorded the treatment and control effect sizes and variance, the sample sizes, latitude, longitude, study year, response type (count, percent cover, rate, etc.), experiment type (turf removal, substrate comparison), plot size (meters2) or container volume (milliliter), whether or not herbivory was experimentally tested, the life-history stage of the canopy species, species identities, and depth (in meters relative to mean lower low water, “MLLW”). When the latitude and longitude was not provided for a study, we used GEOLocate to estimate the location from locality (http://www.museum.tulane.edu/geolocate/ ). When a depth range was reported, the midpoint was recorded. For studies where depth was not reported, we imputed depth as follows. Using information provided in the text, if the study was described as low or mid intertidal, we assigned a depth of +0 and +1.0 m MLLW, respectively (Appendix S1). Generally, “intertidal” refers to studies at depths shallower than 0 m MLLW, while “subtidal” are the zones deeper than the lowest low tide (m MLLW < 0). For four studies, no depth or zone was reported and additional information from the literature was sought to assign depth (Appendix S1). When plot sizes were not standardized among replicates (only Gunnill 1980), plot area was recorded as the midpoint between the two sizes.
When papers reported results from studies replicated at multiple sites or time points, we recorded data from each replicated study in our database. When an experiment tested the effect of multiple factors, we included data from only the treatment most similar to ambient or natural conditions (e.g., a no-nutrient addition treatment, or a canopy-intact treatment). In two studies, the effect of artificial turfs on the canopy was measured. These effects did not differ from the effect of “live” turfs (Appendix S2) and were thus included. When raw data or means and variance estimates were not available in text or tables, we extracted data from figures using ‘digitize’ for R (Poisot 2011; R Core Team 2019).