Temperature variability at the larval scale affects early survival and growth of an intertidal barnacle

For rocky intertidal invertebrates, the transition from pelagic larva to benthic settler represents a critical life-history stage characterised by high mortality. This mortality has been attributed to biotic factors such as predation or individual larval quality, as well as to abiotic factors such as thermal or desiccation stresses. Surprisingly little is known about how temperature varies at very fine spatial scales relevant to newly settled larvae. We used infrared (IR) imagery to determine (1) whether in situ rocky substrates during aerial exposure exhibit repeatable fine-scale (1 mm) temperature variation at the larval scale, and (2) whether the presence of adult conspecifics ameliorates effects of substratum temperature and promotes early growth and survival of settlers. We tracked the settlement and early survival of larvae to determine whether fine-scale variation in temperature influences early life history processes of the intertidal barnacle Tesseropora rosea. Larval settlement did not vary with fine-scale variation in rock temperature, but early post-settlement growth and survival were both inversely related to temperature. Furthermore, we found that rock temperatures decreased significantly with increasing proximity to adult T. rosea and that larvae that settled within 15 mm of adults survived better than those that settled within 16 to 30 mm, highlighting positive effects of gregarious settlement. This is partially explained by conspecific adults shading rock and reducing rock temperatures. We present the first use of IR technology to test for variation in rock temperature at a scale relevant to individual larvae, demonstrating that such fine-scale variation in thermal stress impacts the early-life history stages of a benthic marine invertebrate.