Habitat variability and ecosystem processes in intertidal soft-sediments

Abstract

Coastal and estuarine soft-sediment ecosystems are disproportionately important for ecosystem functioning (on a per m2 scale) as they serve as transitional environments, making them one of the most biologically productive places on earth. This productivity is underpinned by multiple ecosystem processes. Developing a framework to quantify the transformation, sequestration or connectivity of energy and matter across habitats and ecosystems is one of the most significant challenges faced by ecologists and resource managers today. This thesis investigates the influence of habitat variability on ecosystem processes in intertidal soft-sediments, using a variety of direct measures and models. I built upon a connectivity framework developed for populations to inform our understanding of how specific habitats can contribute to ecosystem function in terms of functional performance and the degree to which they sequester or release energy or matter that affects the supply and flow of ecosystem services. Multi-site manipulative experiments revealed how spatial variation in multiple habitat features and disturbance-related shifts in the functional attributes of the community influenced ecosystem function, including a switch in habitat function from a source to a sink of fluxes at some sites. Site-specific combinations of biological, chemical and physical variables explained the different sediment stability metrics, suggesting disturbances that reduce the abundance of large macrofauna can have substantial impacts on ecosystem functioning. Finally, I used empirical data derived from multi-habitat field experiments to parameterise a spatial prioritisation model and evaluate foci for management, which demonstrated shifts in the contribution of different estuarine habitat types to ecosystem provision under scenarios associated with likely disturbances due to future land-based sediment inputs. Integrating different research approaches and extending empirical research across multiple sites is critical if we are to better understand soft-sediment habitats as part of larger ecosystems.