Mediterranean biogeography, colonization, expansion, phenology, and life cycle of the invasive jellyfish Phyllorhiza punctata von Lendenfeld, 1884

There is a widespread belief concerning the increase in the number and intensity of jellyfish blooms, which is partly attributed to the expansion of species that form these blooms. However, the mechanisms of spread for these invasive species beyond human-mediated transportation are still not well understood. In this study, we have compiled a comprehensive dataset of Mediterranean Sea records (1965-2022) for the invasive, bloom- forming species Phyllorhiza punctata von Lendenfeld, 1884, in order to illustrate its spread throughout the Mediterranean basin, the role of coastal lagoons as stepping stones in this process, and its life cycle within Mediterranean waters. The first detection of P. punctata in the Mediterranean Sea dates back to 1965, but de-tections from the 20th century are scarce and widely spaced in time. Since the beginning of the 21st century, the species has spread across nearly the entire Mediterranean Sea. We have identified focal points of expansion in specific semi-enclosed environments such as coastal lagoons or embayments, which act as stepping stones in the colonization process. P. punctata rapidly colonizes these semi-enclosed environments within a short period of time. On a larger spatial scale, an approximate four-year interval is observed between different focal points of expansion. Moreover, in the Mar Menor coastal lagoon in Spain, the presence of a long-term monitoring system has allowed for a description of the colonization and spread mechanisms from the initial observation until the first exportation of individuals to the Mediterranean Sea. The seasonality of P. punctata populations remains consistent across the Mediterranean Sea, with the ephyrae being released after the increase in sea surface temperature in spring, and the medusae remaining in the water column from mid-summer until late autumn or early winter