Methodology:
High-intertidal pools are common in all three regions, allowing us to work at two spatially separated sites in each region. At each site, we identified 18 tide pools, marking each pool and quantifying physical attributes, including surface area, volume, and height on the shore. We also anchored TidbiT temperature datalogger (Onset; Bourne, Massachusetts, USA) in most pools. In the fall of 2017, we identified tide pools and conducted initial surveys and measurements. We repeated surveys every three months until immediately prior to the establishment of grazing experiments at each site in the summer of 2018. These surveys provided insights into the natural temporal variability in community and ecosystem metrics and provided baseline information on relationships between grazer abundances and producer biomass.

Sampling and analytical procedures:
During the quarterly surveys, we quantified consumer abundances, nutrient fluxes, oxygen fluxes, and photosynthetic biomass in each tide pool. Organism abundances were measured by pumping the water from each pool into a bucket, spreading a flexible mesh quadrat over the bottom of the pool, and censusing the algae and invertebrates present in each pool. Nutrient and oxygen fluxes were measured during whole-pool incubations in the dark and in the light.

Pool Characteristics:
Pool characteristics include overall attributes of the tide pools in each of our three study regions. Values were measured at the beginning of our surveys (in October 2017) and refined and remeasured throughout the year (see related dataset "Seasonal Surveys"). Latitude (decimal degrees; values are positive indicating degrees north) and longitude (decimal degrees; values are negative indicating degrees west) were determined for each pool using a Garmin eTrex handheld GPS unit set to WGS84. Tidal elevation (meters above mean lower-low water) was measured using a CST/berger self-leveling rotary laser system. Maximum tidepool depth (cm) was measured using a probe and ruler. Perimeter (m) was measured using a transect tape. Surface area (square count, m2) was measured using a flexible mesh quadrat (Bracken and Nielsen 2004), with 10cm x 10cm squares. Dye volume was determined by adding a known quantity of blue dye to the pool mixing it, measuring it on a spectrophotometer at 640 nm, and relating it to a standard curve relating absorbance to volume (Bracken et al. 2018). Pump volume was determined by pumping the water from each tidepool into a graduated 20L bucket using a hand bilge pump.

This work was conducted at sites located in three regions along the California (USA) coast: (1) Bodega Head, Sonoma County (38.31°N, 123.07°W); (2) Kenneth Norris Rancho Marino Reserve and Hazards Canyon Reef, San Luis Obispo County (35.54°N, 121.09°W and 35.29°N, 128.88°W, respectively); and (3) Corona del Mar State Beach, Orange County (33.59°N, 117.87°W).

Known Problems/Issues:
Some environmentally-related (e.g., tides, darkness) issues caused gaps in the data. These are indicated by "nd".