Local intertidal temperatures
Temperature loggers were wrapped in parafilm and placed inside a PVC cap that was spray painted black and fastened to the substratum using a bolt, wall-anchor and marine epoxy. Temperature was then logged every 4 hours. From July 2012 to May 2013, we also measured intertidal temperatures in the high zone at Foggy Cove, but the cap was the blue top from a Falcon™ tube (Fisher Scientific). We anticipate differences due to the material of the cap, how it was affixed to the rock, and the precise location of the logger, therefore we do not formally compare 2012-2013 data with those from 2014-2016.
Temperature data collected in situ during the study were not sampled over a sufficiently long time period to allow similar retrospective analysis as we performed with data from BC lightstations, but they offer a glimpse into local temperatures during the heatwave that are relevant to intertidal organisms, as well as important differences in thermal environments among sites. Local intertidal temperatures measured in one transect from Foggy Cove before (2012-2013) and during the heatwave (2014- 2016) spanned a range of over 30°C (Fig. S3). Winter temperatures from 2015 were 1°C warmer than the winter of 2016. Additionally, in situ temperatures in the late summer of 2015 more often exceeded the 75th quartile than in 2014, suggesting that high intertidal conditions in 2015 was more stressful than in 2014. Although we cannot directly compare the temperature data from before and during the heatwave, our data suggest that variance in intertidal temperatures may have increased during the heatwave. Rock temperatures were also highly variable across the three sites in our study area based on data from 2015-2016 (Fig. S4). North Beach experienced much longer durations of temperatures exceeding 20° and 30°C than either other site, while Fifth Beach was the only site to never experience in situ temperatures exceeding 30°C during the 2015 deployment. These differences are likely attributable to the physical setting of each site. North Beach faces west and has no barriers to sunlight on clear days, while Fifth Beach faces north and is backed by a vegetated bluff that blocks direct sunlight for much of the day. Foggy Cove differs from the two other sites in that its slope is shallower than the other sites and is characterized by boulders rather than a contiguous rocky outcrop, suggesting a different abiotic stress gradient over similar spatial extents (Fig. S1).