OSIRIS: A model for integrating the effects of multiple stressors on marine ecosystems.

While much has been learnt about the impacts of specific stressors on individual marine organisms, considerable debate exists over the nature and impact of multiple simultaneous stressors on both individual species and marine ecosystems. We describe a modelling tool (OSIRIS) for integrating the effects of multiple simultaneous stressors. The model is relatively computationally light, and demonstrated using a coarse-grained, non-spatial and simplified representation of a temperate marine ecosystem. This version is capable of reproducing a wide range of dynamic responses. Results indicate the degree to which interactions are synergistic is crucial in determining sensitivity to forcing, particularly for the higher trophic levels, which can respond non-linearly to stronger forcing. Stronger synergistic interactions sensitize the system to variability in forcing, and combinations of stronger forcing, noise and synergies between effects are particularly potent. This work also underlines the significant potential risk incurred in treating stressors on ecosystems as individual and additive.