Increases in global temperatures are expected to have dramatic effects on the abundance and distribution of species in the coming years. Intertidal organisms, which already experience temperatures at or beyond their thermal limits, provide a model system in which to investigate these effects. We took advantage of a previous study in which experimental plates were deployed in the intertidal zone and passively warmed for 12 years to a daily maximum temperature on average 2.7°C higher than control plots on the adjacent bedrock. We compared the composition of the biological communities on each experimental plate with its neighboring bedrock control. Plate communities showed decreased richness of taxa and percent cover of filamentous algae, mussels and mobile grazers relative to bedrock, and increased percent cover of biofilm. We then used short-term time-series measurements of plate and bedrock temperatures and a mechanistic heat-budget model to hindcast those temperatures back 12 years. Greater differences in long-term average temperature between the experimental plates and bedrock controls were correlated with lower similarity in community composition. Additionally, years with higher average differences between plate and bedrock temperatures were more predictive of current compositional similarity between plate and bedrock communities, even though they occurred farther in the past than did more recent, but cooler, years. We conclude that current intertidal communities reflect their long-term, rather than short-term, thermal histories. Mechanistic heat-budget models based on short-term measurements can provide this valuable, long-term information.

Heat-budget model output is contained in the .txt files (except Data.txt). The filename indicates whether the hindcasted temperature record is associated with a plate (Plate) or bedrock (Rock) sample, the sample number, whether the record has been summarized daily (maximum daily temperature or daily degree minutes) or yearly (significant annual temperature or significant annual degree minutes), and whether the record was produced by a model optimized to produce the most accurate maximum temperatures (MAX) or degree minutes (DMS). Inside each file, the first column contains maximum temperature data (maximum daily temperature or significant annual temperature) and the second column contains degree minutes data (daily degree minutes or significant annual degree minutes).

Data.txt contains the raw temperature data taken from each plate and bedrock sample in the field between August and October 2013. The first column is always 101. The second, third and forth columns contain the year, day of year and time data. The fifth and final columns contain reference measurements. The 25th column contains no data; this channel on the multiplexer was broken. The remaining columns (six through twenty-eight, skipping twenty-five) contain data from Rock1, Plate2, Plate3, Rock4, Plate7, Plate6, Rock5, Rock8, Plate9, Plate10, Plate11, Rock12, Plate13, Plate14, Plate15, Plate16, Plate17, Rock18, Rock19, Plate21, Rock22 and Plate23. Note that -6999 indicates NaN.

Raw_bio_data.csv contains the counts of sessile and mobile organisms on plate and bedrock samples determined in August and December of 2013 and March and June of 2014. Rows correspond to species surveyed. Columns indicate the month and location of the sample. For example, "AugP2" indicates the organism counts from August 2013 on Plate 2. "Aug2.1", "Aug2.2" and "Aug2.3" indicate the organism counts from August 2013 on the first, second and third randomly-selected, 10x10 cm plots of bedrock adjacent to Plate 2, respectively. These counts were averaged, and represent the biological data corresponding to the Rock1 temperature data.