Figure 3.

Frequency of two consecutive heat-stress bouts based on field Robomussel data. Field data from Robomussels at Hopkins Marine Station [37], where Robomussel temperatures were collected every 10 min for 6–13 consecutive months in each of the years shown in the figure (2005, 2007, 2009 and 2014). The frequency of heat-stress bouts (on the y-axis) is relative to the total number of heat-stress bouts for that given year. The x-axis indicates the total number of days between any two consecutive heat-stress bouts, where a heat-stress bout was defined as any temperature from 28 to 41°C for at least two consecutive hours (see ‘Methods’ for more details). The numbers above the bars indicate the frequency (as a percentage) with which any two heat-stress bouts occurred for that specific number of days apart, relative to the total number of heat bouts for that given year (e.g. in 2007, 37% of heat events occurred 2 days apart). The yellow and red shading behind the bar plots shows the results from our laboratory-based findings for the 30 and 35°C groups, respectively. Note that the primary y-axis values are not applicable to the yellow- and red-shaded trapezoids, which are only meant as a pictorial representation to synthesize the data from the laboratory with the field body temperature data; the secondary y-axis label of ‘Increasing survival’ is simply to show that the trapezoidal shading indicates when survival increased and decreased over time for each of the two experimental groups. Heat tolerance was improved 1 and 2 days after the initial 30 and 35°C sublethal heat-stress bouts, respectively, and starts to decay at 14 and 21 days later, respectively. Note that the 25°C experimental group data are not pictured here as this treatment did not improve survival.