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Key messages  Marine ecosystem degradation involves the loss of benefits to society; it can occur as a result of natural causes or human activity.  Impacts of climate change, including ocean acidification, are inherently global. Widespread local activities can also have cumulative global effects. The many components of both kinds of impacts interact.  The rate of marine ecosystem degradation is accelerating due to economic growth and population growth.  Improved assessments of ecosystem state should be based on integrated, interdisciplinary observations that include biodiversity and ecosystem functioning.  Further international policy action is needed to reduce the drivers of marine degradation, improve marine literacy and develop a global approach to marine conservation.

Representatives of gelatinous zooplankton are increasingly reported in large numbers, with more than 1000 species worldwide, including Cnidaria, Ctenophora and Thaliacea, often collectively known as “jellyfish”. • The reasons for increasing jellyfish blooms are probably manifold, ranging from local to global. Climate change and overfishing are global phenomena, and are good candidates as primary drivers of the rise of gelatinous zooplankton, at least in some parts of the ocean. • Current evidence suggests that sea warming is forcing temperate marine biota towards the poles, with tropicalization of temperate marine ecosystems due to community phase shifts. Climate change is also negatively affecting tropical communities, as exemplified by the increasing frequency of coral bleaching events. Gelatinous zooplankton appear to be expanding their distributions, as seen in the Mediterranean Sea with the increased presence of tropical species, likely favoured by both temperature increases and the progressive enlargement of the Suez Canal. • There is no evidence that temperature rises are threatening tropical jellyfish species, as they are with corals, but this might be due to current lack of observations. • Increases in temperature may broaden the reproductive periods of mid-latitude jellyfish, and improve winter survival of tropical species expanding to temperate waters, therefore boosting both alien and native outbreaks. • Increases in temperature at high latitudes might be detrimental for indigenous species, reducing their reproductive outputs. So far, limited increases in temperature at high latitudes do not support the proliferation of warm-water, non-indigenous species. • The resulting patterns should see a stable situation at low and high latitudes, with no tendency to gelatinous plankton blooms, whereas these phenomena should increase at mid-latitudes, but this speculation needs to be substantiated by focused studies.

This volume contains the main results of the EC FP7 “The Ocean of Tomorrow” Project CoCoNet, divided in two sections: 1) a set of guidelines to design networks of Marine Protected Areas in the Mediterranean and the Black Seas; 2) a smart wind chart that will allow evaluating the possibility of installing Offshore Wind Farms in both seas. The concept of Cells of Ecosystem Functioning, based on connectivity, is introduced to define natural units of management and conservation. The definition of Good Environmental Status, as defined in the Marine Strategy Framework Directive, is fully embraced to set the objectives of the project, by adopting a holistic approach that integrates a full set of disciplines, ranging from physics to bio-ecology, economics, engineering and many sub-disciplines. The CoCoNet Consortium involved scientist sfrom 22 states, based in Africa, Asia, and Europe, contributing to build a coherent scientific community.

The majority of Hydrozoa is represented by not readily noticeable, small species. In recent decades, however, taxonomic knowledge of the group has increased worldwide, with a significant number of investigations focused on the Mediterranean Sea. Over more than two decades, 115 species of hydrozoans were recorded from coastal waters along nearly 300 km of the Salento Peninsula (Apulia, Italy). For each species, records from different collections were merged into single sheets of a general database. For each species, the following information is reported: description, cnidome, biology, occurrence in Salento, worldwide distribution, and bibliography. Descriptions refer to the benthic hydroid stage and, when present, also to the planktonic medusa stage. The 115 species of Hydrozoa, recorded along the Salento coastline, represent 25% of the Mediterranean Hydrozoa fauna (totaling 461 species), and nearly 3% of 3,702 world's known species covered in a recent monograph. Four species are non-indigenous, three of them with invasive behavior (Clytia hummelincki, Clytia linearis, and Eudendrium carneum), and one species now very common (Eudendrium merulum) in Salento. The complete life cycle of Clytia paulensis (Vanhöffen, 1910) is described for the first time.