Dataset: Semibalanus balanoides recruitment surveys in southwest England, Wales, and Scotland from 2015-2016 (EUROWINTER2 project)

Sampling and Analytical Methodology:
Sampling occurred May - June 2015, September 2015, and May - July 2016. Recruitment was sampled at thirty intertidal sites along the west coast of the United Kingdom, encompassing a latitudinal range of approximately 50 to 58 degrees N. Sites were spaced at approximately 50 km intervals, based on estimated dispersal distance for barnacle larvae (Southward, 1967). Five quadrats (15cm x 15 cm) were established at the mid-tidal level at each site. Each quadrat was divided into four sub-quadrats, three of which were scraped completely free of barnacles; the unmanipulated sub-quadrat was a control treatment. The experimental scrapes allowed for the observation of de novo recruitment. Photographic sampling was used to determine recruitment levels. Recruitment density was analyzed for the barnacles Semibalanus balanoides, Chthamalus montagui, Chthamalus stellatus, and Austrominius modestus. Photos of each quadrat were taken using an Olympus TG-4 digital camera, positioned with a focal-framer.

Temperature Methodology:
NOAA Optimum Interpolation Daily Sea Surface Temperature Version 2 (Reynolds et al. 2007) data were obtained from the NOAA National Climatic Data Center https://www.ncdc.noaa.gov/oisst. These daily data are on a 1/4° latitude-longitude grid. For each sample site, the nearest OISST ocean pixel was chosen, and the number of days with Sea Surface temperature (SST) below 10°C between November 1 of the year prior to sampling and February 28 of the year of sampling was determined. These values were categorized into groups: 1=less than 4 weeks below 10°C, 2=four to 6 weeks below 10°C, 3=greater than 6 weeks below 10°C.