Manipulating thermal stress on rocky shores to predict patterns of recruitment of marine invertebrates under a changing climate

For rocky intertidal organisms, temperature is often considered the most influential factor governing early survival and growth. Nevertheless, our review of the literature revealed that few studies have manipulated temperatures in the field to test for effects on these critical early life history processes. Here, we present the results from a novel manipulation of substratum temperature using settlement plates of different colour (black, grey and white) and infrared measurements of temperature to test hypotheses that temperature influences the early survival and growth of recent settlers of the intertidal barnacle Tesseropora rosea. Mean surface temperatures of black and grey plates were as great as 5.8 degrees C (on average 2.2 degrees C) and 4.8 degrees C (on average 1.6 degrees C) hotter than white plates across the sampling period, respectively. Cooler, white plates had significantly greater settlement and early growth than hotter, black plates, but differences in plate temperature did not significantly influence early survival or recruitment, though patterns were consistent with thermal variability. Comparisons between grey coloured natural rock and plates indicate that grey plates thermally mimic natural rock. Nevertheless, on average, more than twice as many larvae settled on plates than on natural rock, but early post-settlement survival on natural rock was double that on plates, suggesting that this artificial surface may not adequately capture the natural variability in early life history processes. Regardless, our simple and repeatable thermal manipulation represents a useful tool for experimentally investigating the effects of temperature on recruitment processes and simulating future temperature variability associated with climate change.