Meeting Abstract
Intertidal organisms use a variety of adaptations to protect offspring from environmental stresses such as desiccation and UV radiation. One adaptation is to attach offspring to safe benthic substrata, as seen in the intertidal sea slug Haminoea vesicula in False Bay, San Juan Island, USA. When preferred substrata are scarce, slugs often lay their ribbon-shaped egg masses in dense clumps, attached to one another instead of directly to the substratum. Clumping may have disadvantages: ribbons in the clump center may be oxygen-deprived, and clumps are frequently dislodged from their substrata by waves and currents, becoming prone to stranding at low tide. However, we hypothesized that stranded clumps provide a survival advantage over stranded single egg ribbons. Ribbons in the clump interior should be shielded from drying and UV exposure. We tested this idea with H. vesicula embryos that were midway through development, at a stage when they spin rapidly in their envelopes. We simulated low tide by exposing individual ribbons and artificial clumps to air and sun for 1 hr., during which we noted cessation of spinning (an indication of stress). Ribbons and clumps were then rehydrated in seawater for 24 hrs., after which survival rates were recorded. Embryos in individual ribbons stopped spinning sooner than embryos at the clump edge, but next-day survival did not differ significantly between these two groups, or between embryos in clump middles and edges. However, significantly more embryos survived in the clump middle than in individual ribbons. These data suggest that egg ribbon clumping can aid survival of embryos stranded at low tide. This may relieve some of the pressure on parents to find ideal laying circumstances.
