Marine Research Findings of the VECTORS Project

This website provides access to the research results of the VECTORS project, which can be used to support marine management decisions, policies and governance as well as future research and investment. VECTORS was a large scale project that brought together more than 200 expert researchers from 16 different countries. It examined the significant changes taking place in European seas, their causes, and the impacts they will have on society.

Extreme ecological events: the importance of deterministic and stochastic drivers of jellyfish outbreaks

Jellyfish blooms are examples of species outbreaks that may have adverse effects on fisheries, human health and tourism, with associated social costs and are therefore of great concern to scientists, policy makers and the public at large123. Jellyfish blooms are increasingly viewed as a deterministic response to escalating levels of environmental degradation and climate extremes. However, a comprehensive understanding of the influence of deterministic drivers and stochastic environmental variations favouring population renewal processes has remained elusive. We used a Bayesian analysis to relate jellyfish outbreaks to time-varying and spatial predictors, including sea surface temperature (SST), chlorophyll-a, geostrophic current velocities and distance from the nearest marine canyon. Then we used a statistical resampling technique (the environmental bootstrap method) to evaluate the influence of stochastic fluctuations in time-varying predictors on the occurrence and return times of jellyfish outbreaks. 


Deterministic processes were more important than the stochastic component of environmental variation in driving jellyfish outbreaks. In particular, our research identified coastal areas near canyons as hot spots of jellyfish outbreaks, suggesting that canyons can funnel P. noctiluca blooms during upwelling.

Our analysis was based on data of jellyfish abundance collected at 243 sites along the Catalan coast from 2007 to 2010. Cross- and along-shore advection by geostrophic flow were important concentrating forces of jellyfish, but most outbreaks occurred in the proximity of two canyons in the northern part of the study area (Fig. 1). The environmental bootstrap analysis indicated a return time of five outbreaks every two years, which was only slightly lower than the return times expected in a century or millennium under stochastic environmental fluctuations (six events). Thus, P. noctiluca outbreaks were unlikely to result from the chance coincidence of environmental events leading to favourable conditions for population renewal. Deterministic environmental factors such as shelf topography, geomorphology and possibly other local hydrological processes appeared more important than stochastic environmental fluctuations in driving P. noctiluca outbre aks. Notwithstanding the importance of deterministic environmental factors, species undergoing outbreaks must possess appropriate life-history traits to enable rapid population growth and quick response to environmental change4. The hypothesis that canyons can funnel jellyfish outbreaks during upwelling5, is appropriate for species such as P. noctiluca that spend their entire life as planktonic organisms. This is a clear example of how the interaction between environmental change and species’ life histories – a key research theme in VECTORS – may lead to ecological surprises.

Relevance for Policy:
  • Common Fisheries Policy
  • Convention on Biological Diversity
  • Directive on Maritime Spatial Planning and Integrated Coastal Management (forthcoming)
  • Environmental Impact Assessment Directive
  • EU Biodiversity Strategy
  • ICZM Protocol to the Barcelona Convention
  • Marine Strategy Framework Directive
  • Water Framework Directive
Further information:

Deliverable 2.1.2: Mechanisms of change in Alien and native species outbreaks

Factsheet: Jellyfish

Benedetti-Cecchi L, Canepa A, Fuentes V, Tamburello L, Purcell JE, Piraino S, Roberts J, Boero F, Halpin P. in press. Extreme ecological events: the importance of deterministic and stochastic drivers of jellyfish outbreaks. 


Lead Author:

Lisandro Benedetti-Cecchi
University of Pisa (UPISA)
Date of research: June 2014

Related articles:

Growth model for jellyfish Pelagia noctiluca 

Impact of jellyfish on fisheries and tourism 

Cod, recruitment, temperature and zooplankton

Connectivity: plaice spawning and nursery areas 

Develop risk assessments leading to best practice

Modelling hotspots of change in the North Sea 

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This project has received funding from the European Union’s Seventh Framework Programme for research, technological development and demonstration under grant agreement no 266445
© Vectors 2015. Coordinated by Plymouth Marine Laboratory.