ABSTRACT: While structurally complex benthic egg capsules can lower the vulnerability of gastropod embryos to a variety of environmental risks, including predation, desiccation, osmotic shock, and bacterial attack, little is known about their ability to shield embryos from ultraviolet radiation (UV). I examined the exposure of benthic egg capsules of the marine intertidal gastropod Nucella emarginata to solar radiation under natural field conditions, and assessed the degree to which capsule walls protect embryos from UV. Although capsules were laid under dense algal canopies at some intertidal sites, at more wave-exposed locales they were deposited in areas directly exposed to solar radiation. Measurement of UV transmittance through the inner and outer wall of these capsules indicated that <5% of incident 300 nm UV-B and <55% of incident 360 nm UV-A radiation entered the capsule chamber. The outer capsule wall was responsible for the majority of UV absorption. Outdoor experiments confirmed that embryos unprotected by the thick outer capsule wall suffered higher mortality than embryos within whole capsules, when exposed to natural solar radiation. The spectral properties of capsule walls differed significantly among populations of N. emarginata, and among capsules laid by different species of Nucella. This variation was associated with intra- and interspecific differences in the thickness of the outer wall. There was no polarity to the UV-absorbing properties of the outer wall of N. emarginata capsules, however, and no evidence of methanol-soluble UV-absorbing compounds. Although the mechanism of UV absorption remains unclear, N.emarginata capsule walls do provide embryos with substantial protection from UV. These findings thus demonstrate an additional protective role for the capsules of benthic marine gastropods.

KEY WORDS: Egg capsules . Gastropoda . Nucella emarginata . Reproduction . UV

Published in MEPS Vol. 136 (1996) on June 6
ISSN: 0171-8630. Copyright © Inter-Research, Oldendorf/Luhe, 1996