A model for temperature control of jellyfish (Cotylorhiza tuberculata) outbreaks: A causal analysis in a Mediterranean coastal lagoon

Large outbreaks of jellyfish populations sporadically appear at the Mediterranean coasts without any self-evident cause creating public distress because of their impact on local ecosystems and economies. The exacerbated sensitivity of coastal societies has not been paralleled with comparable scientific understanding of the causal mechanisms controlling jellyfish population dynamics. Life-cycle and ecosystem complexities obscure the processes underlying medusa outbursts. Here we present evidence that helps explain population outbursts in a common Mediterranean species (Cotylorhiza tuberculata). Using a population-dynamics model and thermal forcing of its life cycle observed abundances of C. tuberculata could be reliably simulated within a coastal lagoon. Medusa populations fluctuate under the simple rule of “the warmer the better”, with collapses after polyp mortality in severe winters and peaks in years with mild winters and long summers. Cause and effect are here resolved to seize the mechanics of climate forcing on jellyfish dynamics, an understanding that can help to explain past and future fluctuations of abundance in a thermally changing ocean.

► We model the physical forcing of Cotylorhiza tuberculata life cycle.
► This model explains population dynamics of this species in a coastal lagoon.
► Population dynamics is very sensitive to small thermal changes.
► Mild winters and long summers cause blooms, cold winters hamper them.