Combined effects of solar radiation and desiccation on the mortality and development of encapsulated embryos of rocky shore gastropods

Intertidal encapsulated embryos may be synchronously exposed to many environmental stressors, but interactions between some of these factors remain poorly understood. Here, the effects of solar radiation and desiccation on embryonic mortality and developmental rates were assessed using laboratory and field experiments. Egg masses of 3 intertidal gastropod species were exposed for 72 h to combinations of spectral (full spectrum, UV-blocked, dark) and daily emersion treatments (control, 15, 30, 60 min). Siphonaria denticulata and Bembicium nanum embryos were expected to be tolerant to emersion and UVR as they are routinely deposited on exposed rock platforms. In contrast, Dolabrifera brazieri embryos were predicted to be vulnerable to these stressors, as they are deposited in shaded, submerged habitats. Laboratory experiments revealed that light treatments and desiccation negatively affected the mortality and developmental rate of D. brazieri. The mortality of B. nanum did not significantly increase after UVR exposure or emersion, and the developmental rate was significantly faster in light treatments than in the dark. Surprisingly, embryonic mortality of S. denticulata was significantly higher in UV-blocked treatments than in full-spectrum treatments after 60 min emersion periods, but neither spectral treatments nor desiccation periods affected developmental rates. Field observations were also conducted to investigate the natural effects of desiccation on the embryonic mortality of S. denticulata and B. nanum. Despite the apparent resistance of these embryos to UVR and desiccation in the laboratory, mortality was significantly higher in desiccated habitats than in submerged habitats in the field, thus suggesting that selection of these spawning sites may not be optimal for embryos, particularly in light of global change