Deterministic Factors Overwhelm Stochastic Environmental Fluctuations as Drivers of Jellyfish Outbreaks.
Jellyfish outbreaks 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. This study quantifies the deterministic and stochastic components of environmental change that lead to outbreaks of the jellyfish Pelagia noctiluca in the Mediterranen Sea. Using data of jellyfish abundance collected at 241 sites along the Catalan coast from 2007 to 2010 we: (1) tested hypotheses about the influence of time-varying and spatial predictors of jellyfish outbreaks; (2) evaluated the relative importance of stochastic vs. deterministic forcing of outbreaks through the environmental bootstrap method; and (3) quantified return times of extreme events. Outbreaks were common in May and June and less likely in other summer months, which resulted in a negative relationship between outbreaks and SST. 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. This result supported the recent hypothesis that canyons can funnel P. noctiluca blooms towards shore during upwelling. This can be a general, yet unappreciated mechanism leading to outbreaks of holoplanktonic jellyfish species. The environmental bootstrap indicated that stochastic environmental fluctuations have negligible effects on return times of outbreaks. Our analysis emphasized the importance of deterministic processes leading to jellyfish outbreaks compared to the stochastic component of environmental variation. A better understanding of how environmental drivers affect demographic and population processes in jellyfish species will increase the ability to anticipate jellyfish outbreaks in the future.
Department of Biology, University of Pisa, CoNISMa, Via Derna 1, Pisa, Italy.
Lisandro
L
Benedetti-Cecchi
Institut de Ciències del Mar, Consejo Superior de Investigaciones Científicas, ICM-CSIC, Passeig Marítim de la Barceloneta, 37-49, 08003 Barcelona, Spain.
Antonio
A
Canepa
Institut de Ciències del Mar, Consejo Superior de Investigaciones Científicas, ICM-CSIC, Passeig Marítim de la Barceloneta, 37-49, 08003 Barcelona, Spain.
Veronica
V
Fuentes
Department of Biology, University of Pisa, CoNISMa, Via Derna 1, Pisa, Italy.
Laura
L
Tamburello
Università del Salento, CoNISMa via Monteroni, 73100 Lecce, LE, Italy; Western Washington University, Shannon Point Marine Center, Anacortes, Washington 98221, United States of America.
Jennifer E
JE
Purcell
Università del Salento, CoNISMa via Monteroni, 73100 Lecce, LE, Italy.
Stefano
S
Piraino
Marine Geospatial Ecology Laboratory, Nicholas School of the Environment, Duke University, Durham, North Carolina, United States of America.
Jason
J
Roberts
Università del Salento, CoNISMa via Monteroni, 73100 Lecce, LE, Italy; CNR-ISMAR, Genova, Italy.
Ferdinando
F
Boero
Marine Geospatial Ecology Laboratory, Nicholas School of the Environment, Duke University, Durham, North Carolina, United States of America.
Patrick
P
Halpin
D000818:Animals; D002980:Climate; D004196:Disease Outbreaks; D017753:Ecosystem; D004777:Environment; D037401:Scyphozoa / Q000254:growth & development*; D012621:Seasons