Climate change jeopardizes species, communities and ecosystem services. An often neglected aspect of climate change are the prospected higher frequencies and intensities of climatic extremes, such as heat waves. The response of species to a changing climate essentially depends on three factors: their physiological ability to cope with changing temperatures; their capacity to adapt, i.e. develop an improved tolerance from generation to generation; and their response to changes in abundance of other species with which they interact, e.g. through competition or predation. This project investigates these three aspects in artifically composed and natural communities of marine benthic invertebrates over time scales spanning one to tens of generations. We will also investigate changes in the microbiomes of selected model species in these communities, and assess whether and how these microbiomes contribute to the fitness of the pertinent species. We will study their physiological tolerances, their ability to adapt to, and the nature and intensity of their interactions under different temperature regimes. We will not only perform lab experiments, but also use their results to construct models which are able to describe the data and predict the response of these populations and assemblages at timescales well beyond what can be tested in the lab. In turn, these models will help us to improve our experimental designs and pinpoint mechanisms that are key to understand the response of nematode communities, and of communities of marine organisms in general, to environmental change. Understanding these responses is crucial to assess climate effects on ecosystem services.