Patterns of jellyfish abundance in the North Atlantic |
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Authors: | Mark J Gibbons Anthony J Richardson |
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Institution: | (1) Department of Biodiversity and Conservation Biology, University of the Western Cape, Private Bag X17, Bellville, 7535, South Africa;(2) Climate Adaptation Flagship, CSIRO Marine and Atmospheric Research, Cleveland, QLD, 4163, Australia;(3) School of Physical Sciences, University of Queensland, QLD, 4072, Australia;(4) Sir Alister Hardy Foundation for Ocean Science, The Laboratory, Citadel Hill, The Hoe, Plymouth, PL1 2PB, UK |
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Abstract: | 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.
Guest editors: K. A. Pitt & J. E. Purcell
Jellyfish Blooms: Causes, Consequences, and Recent Advances |
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Keywords: | Pelagic cnidaria Ctenophora Seasonality Inter-annual Climate change Plankton |
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