Comparative analysis of the ecosystems in the northern Adriatic Sea and the Inland Sea of Japan: Can anthropogenic pressures disclose jellyfish outbreaks?

•We reviewed environmental and ecosystem changes in two LTER sites in the N hemisphere.•We examined the effects of anthropogenic pressures on moon jellyfish populations.•A synchronous shift in climate was detected in the 1980s in both systems.•Providing additional space for polyps, marine urbanisation-enhanced jellyfish population.•Fish-dominated ecosystem switched to “jellyfish-permeated” environment.