Nicolas Djeghri

Université de Bretagne Occidentale | UBO · Institut Universitaire Européen de la Mer (IUEM)

Rhizostomeae species attract our attention because of their distinctive body shape, their large size and because of blooms of some species in coastal areas around the world. The impacts of these blooms on human activities, and the interest in consumable species and those of biotechnological value have led to a significant expansion of research into...

The abundance of large marine dinoflagellates has declined in the North Sea since 1958. Although hypotheses have been proposed to explain this diminution (increasing temperature and wind), the mechanisms behind this pattern have thus far remained elusive. In this article, we study the long‐term changes in dinoflagellate biomass and biodiversity in...

Aim The so‐called regime shifts in North Sea plankton communities provide an important historical case study to understand marine regime shifts. Previous studies characterized regime shifts using a variety of community metrics (e.g., indicator species abundances, taxonomic composition and chlorophyll biomass) but left the functional traits of plank...

The trophic ecology of mixotrophic, zooxanthellate jellyfishes potentially spans a wide spectrum between autotrophy and heterotrophy. However, their degree of trophic plasticity along this spectrum is not well known. To better characterize their trophic ecology, we sampled the zooxanthellate medusa Mastigias papua in contrasting environments and si...

Mixotrophic organisms are increasingly recognized as important components of ecosystems, but the factors controlling their nutrition pathways (in particular their autotrophy–heterotrophy balance) are little known. Both autotrophy and heterotrophy are expected to respond to density-dependent mechanisms but not necessarily in the same direction and/o...

Whereas most jellyfishes are strictly heterotrophic organisms, some of them undergo a photosymbiosis with autotrophic Dinophyceae (“zooxanthellae”). These zooxanthellate jellyfishes, as holobionts, are mixotrophic deriving nutrition from both predation and photosynthesis. However, the relative importance of autotrophic and heterotrophic nutrition c...

Some jellyfish host zooxanthellae in their tissues (mostly from the family Symbiodiniaceae; Dinophyceae) and supplement their heterotrophic nutrition with their symbiont's photosynthates. The mixotrophy of zooxanthellate jellyfishes (as holobionts) renders the study of their nutrition, growth, and population dynamics complicated. Here, we used an e...

We investigated the nutritional plasticity of the zooxanthellate jellyfish Mastigias papua in Palau's marine lake and demonstrate that its nutrition can go from pure heterotrophy to dominant autotrophy. This is, to our knowledge the first field-based characterization of the nutritional plasticity of a zooxanthellate jellyfish. The important nutriti...

We present a summary of the knowledge on zooxanthellate jellyfishes. This presentation is build on our published paper: Djeghri N, Pondaven P, Stibor H, Dawson MN (2019) Review of the diversity, traits, and ecology of zooxanthellate jellyfishes. Mar Biol 166:147

Many marine organisms form photosymbioses with zooxanthellae, but some, such as the medusozoans, are less well known. Here, we summarize the current knowledge on the diversity of zooxanthellate jellyfishes, to identify key traits of the holobionts, and to examine the impact of these traits on their ecology. Photosymbiosis with zooxanthellae origina...

Zooxanthellate jellyfishes rely generally on two contrasted sources of nutrition: predation, and photosynthesis. When studying these organisms, one of the primary questions is to understand how the two sources are balanced relative to each other. We present experimental evidence that isotopic signatures and C:N ratios of zooxanthellate jellyfishes...

There has been an upsurge of interest in trait-based approaches to zooplankton, modelling the seasonal changes in the feeding modes of zooplankton in relation to phytoplankton traits such as size or motility. We examined this link at two English Channel plankton monitoring sites south of Plymouth (L4 and E1). At L4 there was a general transition fr...

The Plymouth L4 time plankton series in the Western English Channel is a textbook example of a shallow, stratifying shelf sea system. Over its 30 yr of weekly sampling, this site has provided a diverse and contrasting suite of numerical and conceptual models of plankton bloom formation, phenology, and seasonal succession. The most recent of these p...

There has been an upsurge of interest in trait-based approaches to zooplankton, modelling the seasonal changes in the feeding modes of zooplankton in relation to phytoplankton traits such as size or motility. We examined this link at two English Channel plankton monitoring sites south of Plymouth (L4 and E1). At L4 there was a general transition fr...

Master 2 Thesis. Internship supervised by Angus Atkinson at the Plymouth Marine Laboratory (UK) in order to obtain the diploma of "Océanographie spécialité Biologie Ecologie Marine" of the Aix-Marseille University (FR)