Alfredo Fernández-Alías

The colonization of the Mediterranean Sea by Cassiopea andromeda underscores the complex interaction of biological, environmental, and anthropogenic factors influencing the spread of invasive species. This study describes the dispersal of C. andromeda across the Mediterranean basin and updates its current distribution. Starting from the initial introduction via the Suez Canal, we uncovered key stages of colonization across the Mediterranean, and discussed the role that salinity, dispersal vectors, and local genetic adaptations might have had in shaping its distribution. Through a comprehensive review of historical records, environmental parameters, and life cycle constraints, we identify three distinct colonization periods: a slow initial colonization, a rapid expansion phase, and a restricted westward spread, culminating in its appearance in the Mar Menor coastal lagoon in southwestern Mediterranean. Our findings suggest that salinity could have acted as a modulator of the spread velocity, delaying colonization in suboptimal conditions and potentially driving local adaptations. This work highlights the synergistic effects of anthropogenic activities and environmental stressors on the spread of marine invasives, providing insights to develop management strategies for C. andromeda and other invasive species in coastal ecosystems.

Jellyfish blooms are dynamic events driven by environmental and anthropogenic factors. This study reports the first documented bloom of the cannonball jellyfish (Stomolophus sp.) in Venezuelan waters, observed between March and April 2024 along approximately 120 km of coastline. Reports from anglers and divers confirmed high jellyfish abundances (~3 ind. m⁻³) across multiple sites. Environmental analyses suggest that fluctuations in sea surface temperature, increased chlorophyll a concentrations, and high precipitation in the preceding months may have triggered strobilation and subsequent bloom formation. However, the polyps have not yet been observed in the field, and advective movement from other locations cannot be ruled out. Given the commercial importance of Stomolophus spp. in neighboring regions, this record underscores the need for continued monitoring to assess potential range expansions and their ecological and socio-economic impacts. Additionally, the emergence of this bloom raises questions about the species’ distribution patterns, potential establishment in Venezuelan waters, and possible implications for local fisheries. Our findings contribute to the broader understanding of gelatinous zooplankton dynamics in the Caribbean Sea and provide baseline information for future ecological assessments and fisheries management strategies. Further studies, including genetic analyses, are needed to confirm species identity and investigate the drivers behind this unprecedented bloom.

The study of jellyfish blooms has gained attention in the recent decades because of the importance of forecasting and anticipating them and avoiding their interference with human activities. However, after thirty years of scientific effort (monitoring systems, empirical laboratory and field studies, modeling, etc.), the occurrence of blooms remains unpredictable, and their consequences unavoidable. Climate change, eutrophication, overfishing, coastal construction, and species translocation have been suggested as stressors that increase them, but robust evidence to support these claims is limited. The widespread belief that jellyfish blooms are “increasing in number” has been challenged in recent years. Among the gelatinous zooplankton, the bloom forming species are concentrated in the class Scyphozoa, and the number of species with at least one recorded bloom has increased during the last decade. The analyses of long-term time series show seasonality in the dynamic of each blooming jellyfish species population, but the blooms vary in intensity and there are years of an unexplained absence of jellyfish. In this review, we focus on the current state of knowledge, uncertainties and gaps in the critical points that can strongly influence the intensity of the bloom or even lead to the absence of the medusa population. These points include ephyrae, planulae and scyphistoma natural, predatory or fishing mortality, the molecular pathway of strobilation, benthic population dynamics, planula settlement and ephyra to medusa transition success. Some of these points account for certain empirical laboratory evidence under controlled conditions, and are difficult to be studied on the field, but the different sources of non-typically recorded variability need to be addressed to improve our understanding of jellyfish population dynamics.

The genus Aurelia is one of the most extensively studied within the class Scyphozoa. However, much of the research was historically attributed to the species Aurelia aurita (Linnaeus, 1758) before the recognition of its taxonomic complexity. Initially considered cosmopolitan and globally distributed, recent phylogenetic analysis has challenged this assumption. Consequently, the current distribution of species within the genus Aurelia and the processes that led to this distribution remain largely unexplored. After genetically confirming that the species traditionally present in the Mar Menor coastal lagoon in the southwestern Mediterranean corresponds to A. solida, we compiled data on the locations where moon jellyfish species have been genetically identified and mapped these coordinates to the geological period when the genus Aurelia diverged from other scyphozoan genera. We propose two hypotheses to explain the disjunct distribution of certain species. The first one assumes recent human-mediated introductions, while the second posits an absence of introductions. Both hypotheses, supported by fossil and historical records, suggest a Paleo-Tethys origin of the genus Aurelia. Migration from this area explains most of the genus’s current distribution without human intervention, being the Mediterranean Sea, where A. solida should be considered autochthonous, part of their natural distribution range.