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Abundance of Pelagia noctiluca early life stages in the western Mediterranean Sea scales with surface chlorophyll

Daniel Ottmann*, Diego Álvarez-Berastegui, Laura Prieto, Rosa Balbín, Francisco Alemany, Øyvind Fiksen, Ana Gordoa, Patricia Reglero

*Corresponding author:

ABSTRACT: Pelagia noctiluca is the most successful and well-studied jellyfish in the Mediterranean Sea. They tolerate a wide range of water temperatures and succeed in low to medium food regimes, but factors driving its distribution and population dynamics remain poorly understood. Here we applied a multiscale analytical approach using survey data and from a physical-biochemical coupled model to assess how environmental factors affect the three-dimensional distribution and seasonal abundance of P. noctiluca early life stages. The surveys took place after the spring bloom, when warm water favors fecundity and growth, but food shortage limits the reproductive investment and early survival. We found that most early life stages of P. noctiluca remain above the shallow thermocline and upper mixed layer where temperature is warm. Their spatial distribution is positively correlated with surface chlorophyll concentration, and over 90% of the variation in interannual abundance is explained by basin-scale productivity in June. Warmer water during winter and spring seasons coupled with protracted spring blooms increase the population of P. noctiluca, and this explains the trend of increasing outbreaks observed in the western Mediterranean Sea over the past decades.