Variability of growth rates and thermohaline niches of Rhizostoma pulmo’s pelagic stages (Cnidaria: Scyphozoa)

Abstract

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.

Biodiversity of Gelatinous Organisms in the Western Adriatic Sea and Identification of Their Echo Traces in Acoustic Data

“…The relationship found between the abundance of R. pulmo and bottom temperature can be more easily explained since a greater amount of research has been dedicated to investigating this parameter's influence on jellyfish compared to other factors. Leoni et al [45] found different kinds of interactions in three Mediterranean lagoons, with optimal temperature and salinity ranges varying among different developmental stages from ephyra to adulthood. Some differences in this aspect were also observed across the studied areas.…”

Multi-platform study of the extreme bloom of the barrel jellyfish Rhizostoma pulmo (Cnidaria: Scyphozoa) in the northernmost gulf of the Mediterranean Sea (Gulf of Trieste) in April 2021

“…The smallest individuals of R. pulmo are often observed in summer (V. Tirelli, personal communication, 2022), but the lack of information about polyps at sea has prevented a complete description of the reproductive cycle of this species. Based on medusae semi-quantitative data and satellite temperature data, Leoni et al (2021a) identified the thermal window of R. pulmo in the Mediterranean sea between 15 and 22 • C, while experimental observations pointed out a potential thermal niche at local scales of 13 to 29 • C (Leoni et al, 2021b). This study confirms the reported range but also shows that the thermal niche of this species is actually larger in the Adriatic Sea, where R. pulmo medusae occurred in winter at temperatures often lower than 10 • C (Fig.…”

Ontogenetic dietary shifts of the medusa Rhizostoma pulmo (Cnidaria: Scyphozoa)

“…Biological samples were gathered biweekly between February and November 2019 in Bages Sigean lagoon (see Figure 1 in Leoni et al, 2021b) between 09:00 and 12:00 AM. The abundances of R. pulmo pelagic stages were estimated using two complementary sampling procedures.…”

“…This scyphomedusa can reach biomasses of 300 tons km -2 during bloom events (Basso et al, 2019), with dramatic effects on fisheries (Nastav et al, 2013) and potentially on the food web structure (e.g., Brodeur et al, 2002). In Bages Sigean, summer blooms of R. pulmo (Leoni et al, 2021b) are a major issue for artisanal fishing due to net clogging, spoiling the commercial value of captured fish and because of the risk of stings (S. Marin pers. comm.).…”

“…In this study, we benefited from the large size range of individuals present across the year in Bages Sigean lagoon (Leoni et al, 2021b) to assess R. pulmo diet throughout the pelagic stages. Owing to the medusa mouths size (ca.…”