Radiation effects along a UV-B gradient on species composition and diversity of a shallow-water macrobenthic community in the western Baltic

Abstract

Although the 'intermediate disturbance hypothesis' (IDH) was originally postulated for marine hard-bottom communities, it has rarely been tested for this community type. We experimentally examined the effects of ambient plus artificially enhanced UV-B radiation (eUV-BR) along an intensity gradient on the abundance of individual species, species composition, and diversity of a macrobenthic community in the western Baltic, Germany. Plots were either exposed each day for 0.5, 1, 2, 4, and 8 h to the maximum expected future UV-BR or were left untreated (= ambient irradiance). Species recruitment and succession on artificial substrata were followed for 5 mo. Transient unimodal patterns for species richness and diversity H ' were produced along the UV-BR gradient early in succession. The density of the competitively superior mussel Mytilus edulis and the abundance of the foliose green alga Ulvopsis grevillei were positively related to UV-BR exposure; suggesting conditions different from those predicted by the IDH-generated unimodal patterns. Protective shading of substratum by U. grevillei and the resultant mitigation of the UV-BR impact for succeeding colonizers may be important in this context. Species composition differed persistently among eUV-BR treatments. In contrast to mussels and U. grevillei, the abundance of red algae was adversely affected by eUV-BR along the disturbance gradient. Our results suggest that expected future UV-BR levels will have limited influence on the diversity of shallow-water macrobenthic fouling assemblages in the western Baltic, whereas their species composition may be affected over longer periods.

Limited evidence of interactive disturbance and nutrient effects on the diversity of macrobenthic assemblages

“…This study has revealed that unimodal diversitydisturbance relationships can result from different processes, corroborating studies of macrobenthic com- (Molis et al 2003). Both the variation in processes generating unimodal diversity patterns as well as the variety in diversity-disturbance relationships themselves (Mackey & Currie 2001) indicate that disturbance alone may not predict community diversity sufficiently well.…”

Ultraviolet radiation shapes seaweed communities

“…Finally, several seaweed species, e.g. green filamentous forms, seem particularly well adapted to recruit at UVexposed sites in the upper eulittoral, i.e., where UV-irradiance is strongest on the shore, and it was experimentally demonstrated that their abundance correlates positively with UV-exposure time (Molis et al 2003). The invasion of sites high on the intertidal shore might be a selective advantage, as this guarantees a relative shorter exposure to grazers compared to sites lower on the shore.…”

“…Only a few studies assessed UV-effects during species succession of shallow-water seaweed-dominated communities (Santas et al 1998;Molis et al 2003;Molis and Wahl 2004;Wahl et al 2004;Dobretsov et al 2005). Surprisingly in all but one study (Dobretsov et al 2005), UV-effects were only apparent during the early phase of succession.…”

Effect of solar ultraviolet radiation on the formation of shallow, early successional biofouling communities in Hong Kong

“…Baker 1995, Bingham & Reitzel 2000, Chiang et al 2003. Only a few studies have examined the effect of UVR on benthic communities (Santas et al 1998a,b, Lotze et al 2002, Molis et al 2003, Molis & Wahl 2004. For example, Santas et al (1998b) investigated the effect of UV-A and UV-B radiation on benthic diatoms in a coral reef in the Caribbean.…”