Coastal systems in transition: From a 'natural' to an 'anthropogenically-modified' state

The structure and functioning of coastal ecosystems are shifting worldwide as a result of natural changes and, even more important, consequences of intense human intervention, of which habitat destruction, over exploitation of resources and environmental pollution are among the most serious. In this context, the 56th Conference of the Estuarine Coastal Sciences Association was held in Bremen, Germany, in September 2016 under the umbrella topic 'Coastal Systems in Transition: From a natural to an anthropogenically-modified state'. The objective of this Special Issue is to demonstrate and synthesize the effects of both, natural variations and human intervention in estuaries and other coastal ecosystems. The 22 articles originate from various disciplines and cover a wide range of ecosystems, including temperate and tropical estuaries, hypersaline lagoons, mangrove forests, coral reefs and coastal dunes. The articles are categorized under four main topics, (1) drivers and dynamics of coastal systems, (2) impacts on estuarine biodiversity and community structure, (3) impacts on estuarine and bay functioning, and (4) management options for protecting estuarine diversity, functions and services. Several of the studies clearly show that estuarine systems are affected by multiple pressures, of which changes in salinity, hydrology, trophic state and habitat complexity as a consequence of human intervention are most frequently addressed. One of the main challenges remains distinguishing between natural and human induced changes in biological, geochemical and physical processes and the interactions between them. A number of studies provide excellent examples of how biological indicators (e.g., benthic and fish diversity and community structure) are suitable for assessing the effects of stressors on ecosystems. It remains an important task to standardize these indicators for easier application in other locations and for evaluating the success of management measures. The high variability of coastal systems, the complex process interactions, and increasing pressure require interdisciplinary studies on a deeper understanding of processes as well as scenario experiments by model applications.