Experimental Evidence of Climate Change Effects on Plankton Community Respiration in European Coastal Waters: Current Insights and Knowledge Gaps in Tested Disturbances and Studied Areas

Plankton community respiration (PCR) plays a central role in aquatic ecosystems, driving the breakdown of organic matter and influencing global carbon cycling through its contribution to the production and consumption of carbon and oxygen. Coastal areas, which serve as critical interfaces between terrestrial and marine ecosystems, are regarded as metabolic hotspots in the oceans, due to their intense biological and biogeochemical activities. Additionally, they are particularly sensitive to the impacts of global climate change. In this regard, this review synthesizes experimental evidence to explore how environmental constraints and climate drivers affect PCR in European coastal waters. In total, 46 studies were found in which PCR was measured during experiments testing the effects of one or multiple global climate change drivers in European coastal waters. Among them, the majority of experiments focused on changes in temperature, nutrient concentrations and stoichiometry, and/or pH, while other stressors were less studied. Many experiments confirmed theoretical predictions, notably regarding the predicted positive effects of increased temperature and nutrient concentrations on metabolism, but more complex responses, often linked to trophic cascade mechanisms and thresholds between positive and negative feedbacks were also often reported. Overall, this review, the first comprehensive synthesis of experimental evidence on PCR in European coastal waters, highlights critical knowledge gaps, notably regarding non- and understudied areas and understudied interactions between stressors that occurs jointly in natural ecosystems. Future research should aim to integrate controlled experiments, long-term monitoring, and modeling approaches to deepen our understanding of PCR dynamics under changing environmental conditions and to predict potential feedbacks to global climate processes.