, Volume 616, Issue 1, pp 51–65 | Cite as

Patterns of jellyfish abundance in the North Atlantic

  • Mark J. Gibbons
  • Anthony J. Richardson


A number of explanations have been advanced to account for the increased frequency and intensity at which jellyfish (pelagic cnidarians and ctenophores) blooms are being observed, most of which have been locally directed. Here, we investigate seasonal and inter-annual patterns in abundance and distribution of jellyfish in the North Atlantic Ocean to determine if there have been any system-wide changes over the period 1946–2005, by analysing records of the presence of coelenterates from the Continuous Plankton Recorder (CPR) survey. Peaks in jellyfish abundance are strongly seasonal in both oceanic and shelf areas: oceanic populations have a mid-year peak that is more closely related to peaks in phyto- and zooplankton, whilst the later peak of shelf populations mirrors changes in SST and reflects processes of advection and aggregation. There have been large amplitude cycles in the abundance of oceanic and shelf jellyfish (although not synchronous) over the last 60 years, with a pronounced synchronous increase in abundance in both areas over the last 10 years. Inter-annual variations in jellyfish abundance in oceanic areas are related to zooplankton abundance and temperature changes, but not to the North Atlantic Oscillation or to a chlorophyll index. The long-term inter-annual abundance of jellyfish on the shelf could not be explained by any environmental variables investigated. As multi-decadal cycles and more recent increase in jellyfish were obvious in both oceanic and shelf areas, we conclude that these are likely to reflect an underlying climatic signal (and bottom-up control) rather than any change in fishing pressure (top-down control). Our results also highlight the role of the CPR data in investigating long-term changes in jellyfish, and suggest that the cnidarians sampled by the CPR are more likely to be holoplanktic hydrozoans and not the much larger meroplanktic scyphozoans as has been suggested previously.


Pelagic cnidaria Ctenophora Seasonality Inter-annual Climate change Plankton 



CPR data used in this study were provided by the Sir Alister Hardy Foundation for Ocean Science (SAHFOS) and are freely available to all researchers ( The authors are grateful to all past and present members and supporters of the CPR survey, especially the shipping industry that voluntarily tows CPRs on regular routes and funders from UK and elsewhere. MJG is grateful to the Royal Society (London) and the National Research Foundation (South Africa) for funding. Dr Chris Lynam (University of St Andrews) is thanked for providing his scyphozoan data from the North Sea, and Dr Matthew Witt (University of Exeter) is kindly thanked for assistance with preparing Fig. 2. We are particularly grateful to Graeme Hays (University of Wales, Swansea), Kylie Pitt (Griffith University) and an anonymous reviewer for improving earlier versions of the manuscript.


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© Springer Science+Business Media B.V. 2008

Authors and Affiliations

  1. 1.Department of Biodiversity and Conservation BiologyUniversity of the Western CapeBellvilleSouth Africa
  2. 2.Climate Adaptation FlagshipCSIRO Marine and Atmospheric ResearchClevelandAustralia
  3. 3.School of Physical SciencesUniversity of QueenslandQLDAustralia
  4. 4.Sir Alister Hardy Foundation for Ocean Science, The LaboratoryPlymouthUK

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