Dataset: Intertidal community diversity surveys at 23 sites in California, USA and Baja California, Mexico across tidal elevations from 2022-2023

We conducted field surveys at 23 sites across California, USA and Baja California, Mexico between April 2022 and October 2023. Sites in northern California and Mexico were surveyed once per year in the spring (total n = 2 surveys per site), and sites in southern California were surveyed in the spring and fall each year (total n = 4 surveys per site). At each site, we laid a 25 m horizontal transect at the top of the intertidal zone (i.e., parallel to the water at the top of the barnacle zone) and 5 vertical transects (perpendicular and extending toward the waterline) at random locations along the horizontal transect. Along each vertical transect, we placed 0.25 m × 0.25 m (0.0625 m²) quadrats every 0.25 m drop in vertical elevation. Within each quadrat, we conducted community diversity surveys where we assessed the relative abundance of all species, both mobile and sessile, as percent cover. Tidal elevation was determined using an Apache Tools Mesa SL101 laser level with reference to tidal predictions from the National Oceanic and Atmospheric Administration.