Assessing the consequences of sea level rise: effects of changes in the slope of the substratum on sessile assemblages of rocky seashores

Abstract

Sea level rise can affect the biodiversity of coastal areas through alterations of features of the substratum, including the geometry of shorelines. Field measurements on the rocky shore of Calafuria (NW Mediterranean Sea) showed that a rise in sea level in the range of 5 to 50 cm would increase the availability of steep substrata (> 40°) for assemblages of algae and invertebrates by up to 58% compared to current conditions. Comparisons between assemblages on horizontal and vertical substrata revealed clear differences in the composition and abundance of common taxa. Clearing experiments replicated on vertical and gently sloping surfaces at 2 heights on the shore were performed to test hypotheses about the role of recruitment and post-recruitment processes in maintaining differences between substrata. Comparisons of recolonizing assemblages with unmanipulated controls allowed us to test the hypothesis that a change in slope of the substratum affected the ability of assemblages to recover after a disturbance. Results indicated that differences in the structure of assemblages between vertical and horizontal substrata were maintained by a combination of recruitment and post-recruitment processes, although the relative importance of these processes differed among taxa. Nonetheless, patterns of recovery of assemblages were comparable between the 2 substrata. These findings suggested that sea level rise, by increasing the proportion of vertical substrata at the expense of horizontal surfaces, will lead to the expansion of assemblages dominated by encrusting coralline algae and grazing gastropods, and the reduction of abundance of filamentous forms and barnacles. The resilience of assemblages, however, appeared unaffected by the aspect of the substratum.

Effects of Climate Change on Global Seaweed Communities

“…Sea‐level rise will result in a general upward shift of benthic communities en masse , although the accompanying changes in the relative availability of appropriate substratum types and orientations at specific shore levels (e.g., on shores with wave cut platforms and cliffs) may drive changes in relative algal abundance (Vaselli et al. ). However, zonation patterns are determined by far more than just position relative to mean sea level.…”

“…Some of the most readily detectable changes are at local (site) scales, where environmental change can result in shifts in the vertical distribution (often termed zonation) of intertidal and subtidal seaweeds. Sea-level rise will result in a general upward shift of benthic communities en masse, although the accompanying changes in the relative availability of appropriate substratum types and orientations at specific shore levels (e.g., on shores with wave cut platforms and cliffs) may drive changes in relative algal abundance (Vaselli et al 2008). However, zonation patterns are determined by far more than just position relative to mean sea level.…”

Assessing Coastal Squeeze of Tidal Wetlands

“…Anthropogenic barriers prevent wetlands from migrating inland, and steep slopes bordering wetlands stall or completely halt wetland migration (Brinson, Christian, and Blum, 1995). We are unaware of any studies that have established the critical slope that prevents marshes from migrating inland, but in a study of rocky coasts, Vaselli et al (2008) defined steep substrata as those areas with a greater than 408 slope. Pavement contributes to coastal squeeze by resisting plant colonization (Lu and Weng, 2006).…”

Inter-individual variation partially explains patterns of orientation on steeply sloped substrata in a keystone grazer, the limpet Cellana tramoserica

“…The behaviour of intertidal animals on steeply sloped substrata has been relatively understudied compared with that of organisms on horizontal substrata and within specific microhabitats (see Della Santina 1994;Della Santina et al 1995;Chelazzi et al 1998;Bulleri et al 2004 for some exceptions). Global sea levels are predicted to rise as a result of climate change (Pachauri and Reisinger 2007), and consequently, the intertidal region may shift in many areas from predominately horizontal surfaces to increasingly dominated by steeply sloped and vertical surfaces (Vaselli et al 2008;Jackson and McIlvenny 2011), and the abundance of different habitat types will change (Thorner et al 2014). In addition to losing natural horizontal habitats, the proliferation of artificial structures, such as seawalls, will also lead to an increase in vertical habitats (Chapman 2006).…”