The world's marine ecosystems face multiple challenges, some natural, but many resulting from humankind's activities. Global climate change, driven by influences of energy usage and industrial practices, is a reality now accepted by most of the world's scientists, media and political establishments. Warming seas and rising sea levels are regarded as threats, while visionaries consider deep ocean carbon disposal as a technological opportunity. Exploitation of the seas continues apace, with repeated concerns over the impact of over-fishing, plus reservations about the environmental effects of marine aquaculture. We need to understand how resilient organisms and ecosystems are to these challenges, while responding by protecting biologically-meaningful areas of the oceans. The subthemes of the 41^st European Marine Biology Symposium address all of these matters.