Aim Global anthropogenic changes have altered biogeography and phenology of marine populations, thereby promoting a spatial reconfiguration in the functioning of marine ecosystems. Among these changes, massive proliferations of jellyfish in temperate latitudes warn of potential alterations in biogeochemical fluxes, ecosystems’ structure and assets, and the services they provide to human welfare. Understanding driving factors shaping large‐scale patterns of jellyfish proliferations is a pressing need in global ecology and sustainability science. Using a comprehensive dataset of the largest blooming scyphomedusae in southern European seas we test, over broad space–time scales, current hypotheses relating jellyfish dynamics to warming and eutrophication. Location Southern European seas. Time period 1875–2019. Major taxa studied Rhizostoma pulmo. Methods We have gathered historical and contemporaneous records of R. pulmo from the Mediterranean and Black Seas over the last two centuries (7,359 records). Generalized statistical models were used to assess the influence of thermal (latitudinal) and productivity (longitudinal) gradients on the biogeographical patterns, and the species’ phenology at large and regional scales. Results Rhizostoma pulmo abundance exhibited an enhanced magnitude and frequency in recent decades, concurrently with positive temperature anomalies. We found that the latitudinal temperature gradient, but not productivity, shaped long‐term bloom intensity and biogeographical patterns of the species. Our analysis further uncovered a significant effect of the interannual variability of spring temperature on the species’ phenology over the period 2008–2018, with warmer springs favouring an earlier start (c. 3 months) and a longer duration (from 5 to 7 months) of jellyfish season. Main conclusions Among the current hypotheses linking jellyfish changes with anthropogenic disturbances, only the warming‐based hypothesis gained support over wide space–time scales, while the eutrophication‐based hypothesis mainly applied at local scales. Hence, biogeographical patterns of R. pulmo are shaped by the latitudinal temperature gradient, while the species bloom dynamics echo variations in ecoregion thermal regimes.
New records of the cubozoan jellyfish Tamoya haplonema in Uruguayan waters are reported together with historical records for the region, and associated with the oceanographic conditions at the moment of the finding. Occurrences of the species are mainly associated with positive Sea Surface Temperature Anomalies especially during summer months when the intrusion of warm oceanic waters to the Uruguayan coastline is stronger. This was particularly strong during 2012-2013, when a dry period enhanced this scenario. This species is the only cubozoan present in Uruguay, with a sporadic occurrence and so far has no appreciated negative effects on public health. However, from observed increasing frequency of positive temperature anomalies it would be reasonable to predict a future southward shift in the latitudinal distribution of T. haplonema. In this context, occurrence of this toxic species along Uruguayan coastal waters must be considered with particular attention to the potential negative impact on tourism and on general public health.
In recent decades, an increase in the abundance and frequency of bloom events has been reported for the scyphozoan Rhizostoma pulmo in the Mediterranean Sea. Understanding such events requires a thorough assessment of the species' population dynamics through environmental windows allowing species development. The semi-enclosed coastal lagoon of Bages Sigean, France (43 degrees 05 ' 12.72 '' N; 3 degrees 00 ' 35.3 '' E) offers an exceptional framework for investigating the population dynamics of the species, and how its growth rates and environmental niches vary over time. Three cohorts starting in April, May and June 2019 were identified, while the overall population growth reached the maximum biomass (10.2 g m(-3)) in July. Bell diameter and total length were identified as the best morphological proxies of biomass estimation. The abundances of the two most abundant copepods' species appear to drive R. pulmo's dynamics in the lagoon. Based on multinomial analysis and using the von Bertalanffy model, different growth rates for juveniles (4.7 and 2.4 mm day(-1)) and adults (1.8 and 0.9 mm day(-1)) were determined for the first two cohorts. Thermohaline niches varied during ontogeny, but also among populations in three coastal Mediterranean lagoons: Bages Sigean (France), Mar Menor (Spain) and Bizerte (Tunisia), shedding light on the metapopulation dynamics of R. pulmo inhabiting the Mediterranean Sea. The pressing need for understanding the dynamics of jellyfish abundances and their impacts on ecosystems, calls for increased efforts on monitoring these populations and their life history traits to parametrize and build reliable ecosystem models.
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