"Properties that control the condition of the pelagic habitat are physical, optical and chemical variables, such as temperature, salinity, currents, oxygen supply, nutrient inputs, pH and alkalinity. These factors can be affected by a number of different human activities, both land- and seabased, which give rise to, e.g. pollution, eutrophication and climate change. Physical exploitation also risks changing fundamental conditions in the pelagic environment, see more in the strategy for D7. The plankton community forms the basis of the marine food web and thus interacts with higher trophic guilds, such as fish, birds and marine mammals. Changes at some level in the food chain can thus affect other levels, so how we, for example, manage fish and seal stocks can indirectly affect the state of the plankton community. The plankton community can also be directly affected by organic pollution, hazardous substances and the introduction of invasive alien species. Monitoring the input of nutrients and hazardous substances, as well as introductions of alien species and fishing activities are included in other monitoring strategies. With today's monitoring, it is difficult to identify the direct causes of changes in state of pelagic habitats, which makes it difficult to link environmental effects to specific human activities. Long time series on the dynamics of the plankton community and also better data on human activities and their impact are necessary to find the right explanatory models. The understanding of the functional parts of the plankton community in the food web also needs to be improved in order to be able to link the effects of changes in the plankton communities to other parts of the food webs, see the strategy for D4. The data collection need to be representative, so that it captures spatial and temporal variation, as well as large-scale climate variations in order to distinguish these from the changes that are due to local or regional impact. The current vessel-based monitoring programme has been designed to cover offshore and coastal waters with a few representative biological stations, thus enabling overall monitoring of the areas. The local monitoring programmes and the coordinated recipient control programmes are largely located in coastal areas where human impact may occur. Through analysis of the species composition of the plankton populations, it is also possible to some extent to distinguish whether changes occur due to climate change or other