Effects of solar radiation on barnacle settlement, early post-settlement mortality and community development in the intertidal zone

Abstract

We examined the role of solar radiation, and particularly the role of ultraviolet radiation (UVR), in regulating small-scale settlement patterns and early post-settlement mortality in the barnacle Balanus glandula, as well as community development of sessile organisms colonizing the upper mid-intertidal zone. Settlement of B. glandula cyprids was similar in treatments with and without UVR, suggesting that UVR does not directly influence site selection by cyprids. Once attached, mortality during the 1 to 2 d period from attachment to metamorphosis ranged from 60 to 100%, and half of the settlers that did metamorphose died during the following 5 d. Mortality during the period from attachment to metamorphosis was significantly lower in locations protected from UVR than in locations exposed to the full spectrum of solar radiation, but only by ca. 10%. Furthermore, UVR exposure had no detectable effect on the mortality rate of metamorphosed early juveniles. Ambient UVR levels also appear to have had little effect on the colonization of mid-intertidal habitats by sessile organisms: our study locations were colonized by 2 sessile invertebrate species and 2 algal species over a period of 2.5 mo in mid-summer, and densities of these species were similar in treatments with and without UVR. Nevertheless, solar radiation dose explained 43 to 65% of the variation in mortality among daily cohorts of B. glandula, and daily cohort mortality was often 100% during periods with the highest doses. This relationship between solar radiation and survival to metamorphosis was likely due to the effect of solar radiation on desiccation and heat stress. The high sensitivity of early postsettlement mortality rates to solar radiation suggests global climate change may significantly alter patterns of survivorship through this critical stage of life. © Inter-Research 2010.