Found some interesting information about Nucella reproduction.
A whelk’s egg capsule provides not only the proper chemical environment for its embryos to develop, but also protection from predators, storms, disease, and other environmental effects. For example, egg capsules of the whelk Nucella spp. are often found in intertidal areas directly exposed to sunlight. Investigations at the Bamfield Marine Sciences Centre, British Columbia into the possible deleterious effects of UV components in sunlight on graph showing survival of embryos of whelks Nucella ostrina when exposed to UV light developing embryos in Nucella spp. show that >90% of damaging UV-B wavelengths are screened out by the capsule wall.