PODOLSKY, R.D.: Is temperature variability good or bad for intertidal embryos?

Development in an intertidal habitat exposes embryos to a suite of potentially stressful conditions, including large and rapid fluctuations in temperature. Embryo masses of the mollusc Melanochlamys diomedia are deposited in soft-sediment tide pools where temperature change on a spring tide can exceed 23°C (up to a peak of 34°C) at a rate of 3°C per hour. Under these conditions, embryos are regularly exposed to temperatures that induce the synthesis of stress (“heat shock”) proteins, indicating that development in this habitat entails frequent protein damage. To evaluate a possible benefit of temperature variation, I measured rates of development to hatching at a range of fixed temperatures and under variable temperatures that mimicked different degrees of tidal exchange. Development was normal and rates increased as a function of fixed temperature up to 26°C, the temperature at which stress protein synthesis is first induced. Similarly, under variable temperatures, development rates increased as a function of increasing temperature variability (and mean), as long as temperatures remained below the stress-protein threshold. Thus, the answer to the title question, “it depends”–rapid development and dispersal from these habitats can benefit from increases in temperature associated with moderate tides, but can also be impeded by exposure to temperature extremes.