Identifying ontogenetic changes in jellyfish diet is fundamental to understand trophic interactions during their life cycle. Scyphomedusae blooms exert major predation pressure on plankton ...communities, although their role in ecosystems has long been misrepresented. This study assesses seasonal and ontogenetic changes in the diet of the scyphomedusa
Rhizostoma pulmo
, one of the largest yet overlooked Mediterranean jellyfish. Medusae gut contents (
n
= 127) were collected during one year in Bages Sigean lagoon, southern France. Results show that the diet composition differs from the availability of prey in the environment with contrasting preferences along ontogeny. Calanoid (70%) and harpacticoid (45.8%) copepods were the most frequent prey and the major carbon contributors for small medusae (bell diameter < 15 cm). In contrast, ciliates (43.5%) were the most frequent prey for large organisms (> 15 cm), which obtain most of their carbon intake from ciliates and fish eggs (20.9%). The overall impact on micro and mesozooplankton showed that small medusae consume 5% of the copepods daily standing stock, while large medusae consumed 8% of ciliates daily standing stock. Our results stress that
R. pulmo
display different trophic pathways along its life cycle, firstly interacting with the classical food web, and shifting afterwards to a greater interaction with the microbial loop.
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°05′12.72″N; 3°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.
This study examined the seasonal distributions of the medusa
along the coasts of the southern Black Sea between Kızılırmak and Yeşilırmak between April 2008 and March 2010. Monthly abundance and ...biomass values were determined, as well as population parameters. The effect of temperature on medusa distribution was also investigated. Results showed that medusa abundance and biomass were highest in autumn, following a period of increased temperature. In contrast, medusa was not observed during the spring season. It was possible to observe the
individuals for five months for the first term of investigation period (2008-2009), and seven months for the second term (2009-2010). The highest abundance value was found to be 10 n/m
(November 2008 and September 2009) and the highest biomass value was 12.587,5 g/100 m
(October 2009).
In Wales, the barrel jellyfish Rhizostoma octopus is commercially harvested to produce high-value medical grade collagen. Although the fishery is presently not regulated, there are concerns how it ...may affect the leatherback turtle (Dermochelys coriacea), which preys on R. octopus in local waters. We combined monitoring data and morphometric and weight measurements in models to estimate the potential impact of R. octopus fishery on foraging turtles. We found a significant quadratic relationship between bell diameter and wet weight of R. octopus, with bell diameter explaining 88% of the variability in wet weight. R. octopus biomass in the Carmarthen Bay varied inter-annually between 38.9 and 594.2 tonnes y−1. The amount of R. octopus needed to satisfy a leatherback turtle’s daily energetic requirements was estimated at 85.1–319.1 kg. Using leatherback turtle sighting data, our models show that during a jellyfish ‘low year”, the R. octopus population could be completely depleted by an average of two foraging turtles along with the current level of commercial harvesting (4.3 tonnes). During a jellyfish “high year”, the current level of commercial harvesting is predicted to have relatively little impact on food supply for even the maximum number of foraging leatherback turtle reported in the area. However, uncertainties related to the jellyfish’s life cycle in the local waters need to be resolved for proper management of this emerging fishery.
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