Species-specific vulnerability of benthic marine embryos of congeneric snails (Haminoea spp.) to ultraviolet radiation and other intertidal stressors.

We used field surveys and multi-factorial experiments to examine synergistic effects of ultraviolet radiation (UVR) and low tide conditions on the embryonic mortality of two bubble-shell snail species that deposit gelatinous egg masses in intertidal mudflats: Haminoea zelandiae from New Zealand, and Haminoea vesicula from Washington, USA. Egg masses of both species were predominantly found in shallow pools at low tide, and a substantial proportion of both were found in sunny as well as shaded microhabitats. Both exposure to sun and desiccation led to increased embryonic mortality for naturally deposited egg masses of H. zelandiae compared to those that were shaded or submerged. For H. vesicula, although mortality was double for embryos within desiccated egg masses, there was no additional mortality due to sun exposure. In manipulative experiments, UVR and low tide conditions increased embryonic mortality for both species; however, H. zelandiae appeared to be more vulnerable to UVR, whereas H. vesicula was particularly vulnerable to desiccation. Simulated tidal pool conditions significantly increased mortality only for H. vesicula. These results suggest an important role of species-specific differences in vulnerability to different stressors, even for ecologically similar congeners; here, these differences may be related to development time or egg mass characteristics.