Sampling and Analytical Procedures:
This study was conducted on a set of tide pools on a rocky shoreline at John Brown's Beach (57.05 N, 135.37 W), near Sitka, Alaska, USA. We selected 36 tide pools for the light/dark incubation experiments during the first year of the experiment (2018), and sampled sets of those 36 pools in the following two years. The light/dark incubation trial method is separated into three phases: initial, dark, and recovery. We recorded the time that each measurement was taken throughout the experiment. Dates and times are recorded in local Alaska Standard / Alaska Daylight Time. Refer to the attached Supplemental File "Tide_Pool_Characteristics.csv" for additional data characterizing each tide pool (e.g maximum depth, perimeter, volume, etc.)

We began each phase with a set of "ocean" measurements, which were collected from shallow (<0.5m) water adjacent to the shoreline. We measured salinity, dissolved oxygen, temperature, pH, and light (just below the water's surface). During the remainder of the initial phase, we visited each tide pool and measured salinity, dissolved oxygen, temperature, pH, and light (just below the water's surface in the center of the pool). We then secured an opaque black plastic tarp over the tide pool for a duration of 30-45 minutes.

We revisited each pool after this dark incubation period and repeated the salinity, dissolved oxygen, temperature, and pH measurements prior to removing the tarp. We then removed the tarp to measure light. We allowed each pool to recover, un-covered, for another 30-45 minute period before collecting a third round of measurements of salinity, dissolved oxygen, temperature, pH, and light.

Known Problems/Issues:
There are small gaps in the data, primarily from light measurements which were not collected in the field during some sampling periods. These gaps in the data include the absence of light measurements for the ocean in the initial and dark phases on 7/1/18, the absence of light measurements from the dark phase on 1/18/19, the absence of any ocean measurements for the initial and dark phases on 8/5/19, and the absence of a recovery phase light measurement in pools 29-32 and the ocean on 6/27/20.

There were also a pair of tide pools (22 and 23) in the original 36 which were connected, preventing accurate volume measurements from being taken.

Related References:
The light/dark incubation method is also outlined in the methods of Warming and Elevated CO2 Interact to Drive Rapid Shifts in Marine Community Production (Sorte and Bracken, 2015) and Assessment of a field incubation method estimating primary productivity in rockpool communities (Noel et al., 2010). The multipoint calibration protocol used with the Hanna Instruments 9829 Multiparameter Meter is thoroughly described in SOP 6a in the Guide to Best Practices for Ocean CO2 Measurements (Dickson, Sabine & Christian, 2007).