Jellyfish at Cala Figuera (Calvia) in spring 2016. | Michel's


The results of a six-year study of the relationship between marine environmental conditions and the distribution and volume of jellyfish have been published in the journal Marine Ecology Progress Series.

Researchers from the Spanish Institute of Oceanography (IEO), the Balearic Islands Coastal Observation and Prediction System, the Andalusian Institute of Marine Sciences and the University of Bergen in Norway have looked at how warm water favours the growth and reproduction of jellyfish.

They have combined satellite data and analysis of samples from the Bluefin Tuna project in concluding that the most common jellyfish in the Mediterranean, 'Pelagia noctiluca', stays towards the surface of the water, even though food (phytoplankton) is more abundant at lower levels. The study indicates that the jellyfish are most found where there are high concentrations of surface chlorophyll, which determines "90% of changes in their annual abundance around the Balearic Islands".

Therefore, high winter and spring temperatures, together with prolonged spring periods of microscopic algae production, favour the proliferation of Pelagia noctiluca, which generally appears in early summer. As global warming is creating these conditions, this may account for the massive arrival of Pelagia noctiluca in the western Mediterranean in recent decades.

The lead author of the study, Daniel Ottmann at the IEO's Balearic centre, says that the study is important in understanding the behaviour of the Mediterranean's most abundant jellyfish and in being able to predict its "massive proliferation".