Comparative analysis of the ecosystems in the northern Adriatic Sea and the Inland Sea of Japan: Can anthropogenic pressures disclose jellyfish outbreaks? Tjaša Kogovšek a, ⁎, Martin Vodopivec a , Fabio Raicich c , Shin-ichi Uye b , Alenka Malej a a Marine Biology Station, National Institute of Biology, Slovenia b Graduate School of Biosphere Science, Hiroshima University, Japan c CNR – Institute for Marine Sciences, AREA Science Park Trieste, Italy HIGHLIGHTS • We reviewed environmental and eco- system changes in two LTER sites in the N hemisphere. • We examined the effects of anthropo- genic pressures on moon jellyfish popu- lations. • A synchronous shift in climate was de- tected in the 1980s in both systems. • Providing additional space for polyps, marine urbanisation-enhanced jellyfish population. • Fish-dominated ecosystem switched to “jellyfish-permeated” environment. GRAPHICAL ABSTRACT abstract article info Article history: Received 31 August 2017 Received in revised form 23 December 2017 Accepted 2 January 2018 Available online xxxx A prominent increase in the moon jellyfish (genus Aurelia) populations has been observed since 1980 in two semi-enclosed temperate seas: the northern Adriatic Sea and the Inland Sea of Japan. Therefore, we reviewed long-term environmental and biotic data from the two Long-Term Ecological Research (LTER) sites, along with the increase in the moon jellyfish occurrence to elucidate how these coastal seas shifted to the jellyfish-domi- nated ecosystems. The principal component analysis of atmospheric data revealed a simultaneous occurrence of similar climatic changes in the early 1980s; thereafter, air temperature increased steadily and precipitation de- creased but became more extreme. Accordingly, the average seawater temperature from March to October, a pe- riod of polyps' asexual reproduction i.e. budding, increased, potentially leading to an increase in the reproductive rates of local polyp populations. Conspicuous eutrophication occurred due to the rise of anthropogenic activities in both areas from the 1960s onwards. This coincided with an increase of the stock size of forage fishes, such as anchovy and sardine, but not the population size of the jellyfish. However, by the end of the 1980s, when the eu- trophication lessened due to the regulations of nutrients loads from the land, the productive fishing grounds of both systems turned into a state that may be described as ‘jellyfish-permeated,’ as manifested by a drastic de- crease in fish landings and a prominent increase in the intensity and frequency of medusa blooms. A steady in- crease in artificial marine structures that provide substrate for newly settled polyps might further contribute to the enhancement of jellyfish population size. Elevated fishing pressure and/or predation by jellyfish on ichthyoplankton and zooplankton might jeopardize the recruitment of anchovy, so that the anchovy catch has Keywords: Aurelia aurita Climate change Eutrophication Marine urbanisation Forage fish LTER Science of the Total Environment 626 (2018) 982–994 ⁎ Corresponding author. E-mail address: tjasa.kogovsek@nib.si (T. Kogovšek). https://doi.org/10.1016/j.scitotenv.2018.01.011 0048-9697/© 2018 Elsevier B.V. All rights reserved. Contents lists available at ScienceDirect Science of the Total Environment journal homepage: www.elsevier.com/locate/scitotenv