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

Abstract

Four meroplanktonic scyphomedusae, Aurelia aurita, Chrysaora hysoscella, Cotylorhiza tuberculata and 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.

Culture and growth of the jellyfish Pelagia noctiluca in the laboratory

“…These seasonal changes may be linked to the annual reduction in the plankton density after the spring bloom and, consequently, the food available, provided by from a regular plankton tow. Therefore, if the bloom period is weak or climatically shortened (Vandromme et al 2011), growth may be inhibited and the probability of survival of the P. noctiluca population reduced, leading to the presence−absence periods observed in the past (Goy et al 1989, Kogovšek et al 2010.…”

“…In the Mediterranean Sea, P. noc-tiluca has been a recurrent problem for centuries (Goy et al 1989). It has historically been observed to be present or absent for several consecutive years, with a periodicity of 10−12 yr (Goy et al 1989, Kogovšek et al 2010 attributed to climatic forcing. However, since 1994 this species has been present almost continuously in the Ligurian Sea, NW Mediterranean (Bernard et al 2011, L. Berline & F. Lombard pers.…”

Digestion times and predation potentials of Pelagia noctiluca eating fish larvae and copepods in the NW Mediterranean Sea

“…Although P. noctiluca has been studied in only a few locations, primarily in Irish waters (Doyle et al 2008, Bastian et al 2011) and the Mediterranean Sea, this species is found in tropical to temperate oceans around the world (Kramp 1961). Studies suggest that blooms of P. noctiluca and other species have increased in frequency and duration in the Mediterranean Sea (Daly Yahia et al 2010, Kogovšek et al 2010, Licandro et al 2010, Bernard et al 2011. If cnidarian and ctenophore populations increase around the world, as evidence from some locations suggests (Brotz et al 2012, Condon et al 2013, there could be increasing predation on ichthyoplankton and mesozooplankton and increasing detrimental effects on fish populations.…”

“…One species of particular concern is the holoplanktonic species Pelagia noctiluca that has caused economic damage to aquaculture in northern Europe (Doyle et al 2008, Raffaele 2013 and to tourism, fisheries, aquaculture, and energy industries in the Mediterranean (reviewed by Mariottini et al 2008, Canepa et al 2014. P. noctiluca has a long history of blooms in the Mediterranean Sea (Goy et al 1989) that appear to be increasing in frequency and duration (Daly Yahia et al 2010, Kogovšek et al 2010, Licandro et al 2010, Bernard et al 2011.…”

Is it possible to determine the economic impact of jellyfish outbreaks on fisheries? A Case Study – Slovenia

“…Due to the early establishment of research centres along the northern Adriatic shores, historical data relative to jellyfish are available, which have allowed Kogovšek et al (2010) to reconstruct a two-century time series and analyse the recurrence of jellyfish outbreaks. This information was used as a baseline for jellyfish presence in our study.…”