Coastal areas undergo intense and continuous environmental stress derived from multiple land and sea-based human pressures. Eutrophication is a process driven by the enrichment of water by nutrients. The immediate biological response of eutrophication is increased primary production reflected as increased phytoplankton and/or macroalgal abundance. These are ’direct effects’ and indicate the first stages of eutrophication. ’Indirect effects’ such as oxygen depletion, the loss of seagrass and occurrences of nuisance and toxic blooms (i.e. Harmful Algal Bloom) indicate more well developed problems. Water eutrophication has become a worldwide environmental problem, indeed, within only a few decades, numerous oligotrophic coastal areas have undergone a shift to more mesotrophic and eutrophic conditions resulting in an increase in phytoplankton and macroalgal biomass, increased incidences of toxic and noxious algal blooms, consequent hypoxia and anoxia, loss of biodiversity and violations in the chemical elements transformations (i.e. release of toxic heavy metals, production of methylmercury). The variation of nutrient loadings also cause a change in nutrient ratios (N:P:Si), which may produce an ’undesirable disturbance’ in the marine ecosystems. The major influencing factors on water eutrophication include nutrient enrichment, hydrodynamics and environmental factors such as temperature, salinity, carbon dioxide (CO₂), element balance. The occurrence of water eutrophication is actually a complex function of all the possible influencing factors, thus it is important to study the mechanisms of eutrophication in order to understand the ecosystem functioning. Climatic variations are supposed to be a critical factor affecting the stratification of the waters and the intensity of hypoxia, and impacting on availability and transformation of nutrients and organic matter from land to the sea. Ocean acidification, rising temperatures, and increased intensity of rain events and river runoffs are occurring due to climate change and could enhance eutrophication processes. The ways in which human activities interact with climate are multi-fold. For example, hypoxia and anoxia are created in part by agricultural runoff and physiological effects of hypoxia vary with temperature and CO₂ concentration. Moreover, while acidiﬁcation in the open ocean is mainly driven by the atmospheric CO₂, in coastal zones the signal of CO₂-induced acidiﬁcation might not be readily discernible, particularly at eutrophic marine areas where excessive nutrient loading and organic matter production have been associated with hypoxic events and acidification is also due to microbial degradation of organic matter. The interaction between climate and other anthropogenic variables may exacerbate climate-induced changes in marine ecosystems. Changes in climate in relation to anthropogenic pressures affect the marine ecosystem in a cumulative and potentially synergistic way resulting to possible changes in biogeochemical processes and interactions.

Contributions on the following are welcome:
- Tools and models for eutrophication assessment, including changes over time;
- Biogeochemical consequences of nutrient enrichment; interactions between eutrophication and biological communities;
- Trends in anthropogenic pressures enhancing/reducing eutrophication;
- Interactive effects of climate variability and nutrient enrichment;
- Ecosystem comparisons across the global gradient of nutrient enrichment;
- Eutrophication effects on ecosystem services;
- Challenges and successes at managing eutrophication.

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Frontiers in Marine Science

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