Using infrared imagery to test for quadrat-level temperature variation and effects on the early life history of a rocky-shore barnacle
Most rocky intertidal studies examine early life-history processes at the quadrat level, but few, if any, have measured temperature variation at this scale in the field. This is surprising because the early life stages of rockyshore invertebrates are considered particularly vulnerable to thermal and desiccation stresses and recruitment processes play a key role in structuring adult populations. We used infrared imagery to quantify in situ variation in rock temperatures during aerial exposure among 35 to 50 400-cm2 quadrats (a typical size utilized in intertidal studies). We test whether natural variation in or experimental manipulation of free space, a potential limiting resource, influences temperature variability among quadrats. We then ask whether quadrat-scale temperature variability and the availability of free space influence the early life-history processes of the habitat-forming barnacle Tesseropora rosea in southeastern Australia. Rock temperatures within quadrats separated by tens of meters differed by up to 8.2uC and temperatures within both natural and manipulated quadrats were positively related to free space. Early postsettlement performance was significantly related to this quadrat-scale temperature variability. In unmanipulated quadrats with 100% free space, settlers in consistently ‘‘warmer’’ quadrats displayed reduced early growth and survival compared with settlers in consistently ‘‘cooler’’ quadrats (growth: r2 5 0.48, p 5 0.001, n 5 18; survival: r2 5 0.41, p , 0.01, n 5 17). Although rock temperatures varied significantly with free space, early postsettlement growth and survival did not. Our results highlight both the strong response of early life stages to large natural variation in rock temperatures and the consequent importance of considering quadrat-scale temperature variation in future manipulative experiments.