Assessing the consequences of environmental impacts: variation in species responses has unpredictable functional effects

Many biological processes underpin ecosystem functioning and health. Determining changes in these processes following disturbance is crucial in assessing the wider impacts on ecosystem function and ultimately ecosystem services. Whilst the focus is often on whether disturbance drives changes in ecosystem function through mortality, sub-lethal effects on the physiology and behaviour of organisms may also have cascading effects on ecosystem processes, functions and services. This mesocosm study investigates the effects of a severe short-term exposure (8 days) to a simulated environmental impact—a leak of a subsea geological CO2 capture and storage (CCS) reservoir—on key biological processes (bioturbation), an ecosystem function (nutrient cycling) and on the functional group composition for seven common benthic invertebrate species. Here we statistically allocate species to functional effect groups based on their measured functional effect relative to other species. Following exposure, we observed behavioural responses driving changes in bioturbation for several species and altered nutrient cycling. Responses were species specific and resulted in shifts in functional effect group composition for some key nutrients (nitrate and silicate). We show that the allocation of species to functional groups by measuring specified ecosystem processes and functions can change following environmental perturbations. This implies that whilst biodiversity and ecosystem functioning are intricately linked, maintaining species identities and abundances after environmental perturbation is no guarantee to maintaining ecosystem functions, as species alter their rate and mode of activity following an environmental stress.