Causes and consequences of variability in marine benthos

Abstract

The last two decades have seen a shift of emphasis in ecology; from a focus on the drivers of biodiversity change toward a consideration for its effects on ecosystem functioning. Ecosystem functioning is affected by individual species (i.e. species with functionally dominant biological traits), but can also be influenced by other factors, such as interspecific interactions. Current evidence suggests that biotic influence over marine ecosystem functioning is largely underpinned by the effects of individual species. However, there are indications that this might not constitute a complete understanding of the link between marine biodiversity and ecosystem function (BEF). For this thesis, I applied our current understanding of marine BEF relationships (i.e. the causal link between particular biological traits and particular ecological functions) to long-term benthic community time series and investigated the causes of ecological change and its consequences for ecosystem functioning. A shift in the taxonomic composition of the species assemblage was explained by underlying variation in extrinsic drivers. However, the long-term conservation of trait composition suggests that functioning can be sustained in the face of environmental and ecological change. Experiments conducted to test BEF relationships in intertidal marine benthos reaffirmed the functional importance of the biological traits of species, but also showed that interactions among species can influence the delivery of ecological functions in various ways, including facilitation (i.e. function delivery is enhanced) and antagonism (i.e. function delivery is reduced). The results suggest that biotic influence over marine ecosystem functioning is more complex than previously suggested, and that the impacts of biodiversity change (e.g. species extinctions or shifts in species densities) could be either exacerbated or mitigated depending on the composition of the affected assemblage and the ecological function considered. To produce more realistic results, future indirect assessments of ecosystem functioning would benefit from incorporating interactions among species as well as their biological traits.