Dr. Charlotte Havemans

Over recent years, the worldwide impact of jellyfish outbreaks has become more evident. It is assumed that the world ocean is undergoing a general increase in jelly biomass and blooms. However, these assumptions are under debate, since jellyfish are difficult to sample, long-term datasets are missing and their natural “boom-and-bust” cycles add even more complexity to evaluate the role of anthropogenic stressors and climate change. Several jellyfish are competing with fish for the same planktonic food, and some of them also feed on fish larvae and eggs. Therefore, their increased outbreaks have led to catastrophic collapses of commercially important fish stocks in some regions. The rapidly changing Arctic and surrounding shelf seas are responsible for 10% of global fisheries. Boreal fish stocks are expanding northward in the Arctic shelf seas. These and also typical cold-water species like polar cod, may be impacted by a regional “jellification”. However, there are no data on abundances of jellyfish in the Arctic and their role in the food web is not yet understood. We will present the current knowledge and recent insights on Arctic jellyfish, but also discuss the increase of gelatinous plankton (salps) in the Southern Ocean, and their potential impact on the ecosystem. Finally, some interesting facts on jellyfish ecology will be presented, as well as the newly developed methods that allow us to study them.