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Recurrence of bloom-forming scyphomedusae: 3 wavelet analysis of a 200-year time series

March 12, 2014

Four meroplanktonic scyphomedusae, Aurelia auritaChrysaora hysoscellaCotylorhiza tuberculataand Rhizostoma pulmo, and the holoplanktonic, non-resident Pelagia noctiluca have formed blooms in the northern Adriatic over the last 200 years. Published data about the historical occurrences of these five scyphomedusae, in combination with our data, were used to analyse their long-term fluctuations in this northernmost part of the Mediterranean Sea. Analysis of the most recent blooms was complemented with environmental descriptors (temperature, salinity, pH, chlorophyll a, zooplankton dry weight and major river discharges). Continuous wavelet transformation analysis of the historical time series of scyphomedusae occurrences and environmental parameters revealed that the five species have been present regularly in the northern Adriatic over the last 200 years, with two major periods of jellyfish proliferations. The first period in the years around 1910 was characterised by significant periodicity of 8–12 years for each species, while the second period from the 1960s onwards was characterised by a shortened significant periodicity of less than 8 years.Pelagia noctiluca fluctuations were analysed in greater detail for the last four decades, revealing significant periodicities of ~10 years, 2.5 years, 8–14 months, and 8 months. The significantly marked periodicity of about 10 years in the P. noctiluca spectrum indicates a pattern similar to that observed in the western Mediterranean. Wavelet analysis showed that the periodicity of occurrence of five jellyfish species has shortened in recent decades and the recurrence of blooms has increased, particularly for A. aurita and R. pulmo.

  • Kogovšek T,
  • Bogunović B,
  • Malej A, 2010: Recurrence of bloom-forming scyphomedusae: 3 wavelet analysis of a 200-year time series, Hydrobiologia, 645:81–96, doi:10.1007/s10750-010-0217-8. Article.

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