Unravelling temporality and environmental drivers of jellyfish presence in an urban beach

Jellyfish blooms affect human activities, causing negative socio-economic impacts. Many questions regarding the presence of these invertebrates remain unknown, including when and why they appear. The aim of this study was to unravel when and which environmental drivers drive the arrival of jellyfish to the urban beach of Las Canteras (Canary Islands), by taking advantage of a long-term temporal series on jellyfish stings and semi-qualitative abundances of three jellyfish species (Physalia physalis, Velella velella and Pelagia noctiluca), provided by the Red Cross rescue service. First, we described inter- and intra (seasonal) annual patterns. Then, daily patterns in stings and monthly jellyfish abundances, by means of a model selection strategy, were connected with daily and monthly environmental drivers (zooplankton biomass, Sea Surface Temperature, SST, wind intensity, as well as climatic indices related to El Niño and La Niña events). We detected a strong seasonal trend in the number of jellyfish stings, with larger values in spring and summer relative to autumn and winter. Physalia physalis and Velella velella appeared during winter, which was also revealed by the model selection approach on the effect of environmental predictors (SST, in particular) on their abundances. In contrast, Pelagia noctiluca -the most abundant species - was present all year round, with the summer months as those with the highest abundances. There was a significant correlation between the daily number of stings and the daily presence of Pelagia noctiluca over time. In brief, the occurrence of the three jellyfish species, in the study area, is seasonally partitioned, with SST over time as the most relevant environmental predictor of both the number of stings and the abundances of the three jellyfish species.