Nutrient patchiness, phytoplankton surge-uptake, and turbulent history: a theoretical approach and its experimental validation

Despite ample evidence of micro- and small-scale (i.e., millimeter- to meter-scale) phytoplankton and zooplankton patchiness in the ocean, direct observations of nutrient distributions and the ecological importance of this phenomenon are still relatively scarce. In this context, we first describe a simple procedure to continuously sample nutrients in surface waters, and subsequently provide evidence of the existence of microscale distribution of ammonium in the ocean. We further show that ammonium is never homogeneously distributed, even under very high conditions of turbulence. Instead, turbulence intensity appears to control nutrient patchiness, with a more homogeneous or a more heterogeneous distribution observed under high and low turbulence intensities, respectively, under the same concentration in nutrient. Based on a modelling procedure taking into account the stochastic properties of intermittent nutrient distributions and observations carried out on natural phytoplankton communities, we introduce and verify the hypothesis that under nutrient limitation, the “turbulent history” of phytoplankton cells, i.e., the turbulent conditions they experienced in their natural environments, conditions their efficiency to uptake ephemeral inorganic nitrogen patches of different concentrations

Distribution of picophytoplankton communities from brackish to hypersaline waters in a South Australian coastal lagoon

Background Picophytoplankton (i.e. cyanobacteria and pico-eukaryotes) are abundant and ecologically critical components of the autotrophic communities in the pelagic realm. These micro-organisms colonized a variety of extreme environments including high salinity waters. However, the distribution of these organisms along strong salinity gradient has barely been investigated. The abundance and community structure of cyanobacteria and pico-eukaryotes were investigated along a natural continuous salinity gradient (1.8% to 15.5%) using flow cytometry. Results Highest picophytoplankton abundances were recorded under salinity conditions ranging between 8.0% and 11.0% (1.3 × 106 to 1.4 × 106 cells ml-1). Two populations of picocyanobacteria (likely Synechococcus and Prochlorococcus) and 5 distinct populations of pico-eukaryotes were identified along the salinity gradient. The picophytoplankton cytometric-richness decreased with salinity and the most cytometrically diversified community (4 to 7 populations) was observed in the brackish-marine part of the lagoon (i.e. salinity below 3.5%). One population of pico-eukaryote dominated the community throughout the salinity gradient and was responsible for the bloom observed between 8.0% and 11.0%. Finally only this halotolerant population and Prochlorococcus-like picocyanobacteria were identified in hypersaline waters (i.e. above 14.0%). Salinity was identified as the main factor structuring the distribution of picophytoplankton along the lagoon. However, nutritive conditions, viral lysis and microzooplankton grazing are also suggested as potentially important players in controlling the abundance and diversity of picophytoplankton along the lagoon. Conclusions The complex patterns described here represent the first observation of picophytoplankton dynamics along a continuous gradient where salinity increases from 1.8% to 15.5%. This result provides new insight into the distribution of pico-autotrophic organisms along strong salinity gradients and allows for a better understanding of the overall pelagic functioning in saline systems which is critical for the management of these precious and climatically-stress ecosystems

Prokaryotic aminopeptidase activity along a continuous salinity gradient in a hypersaline coastal lagoon (the Coorong, South Australia)

The distribution and aminopeptidase activity of prokaryotes were investigated along a natural continuous salinity gradient in a hypersaline coastal lagoon, the Coorong, South Australia. The abundance of prokaryotes significantly increased from brackish to hypersaline waters and different sub-populations, defined by flow cytometry, were observed along the salinity gradient. While four sub-populations were found at each station, three additional ones were observed for 8.3% and 13.4%, suggesting a potential modification in the composition of the prokaryotic communities and/or a variation of their activity level along the salinity gradient. The aminopeptidase activity highly increased along the gradient and salinity appeared as the main factor favouring this enzymatic activity. However, while the aminopeptidase activity was dominated by free enzymes for salinities ranging from 2.6% to 13.4%, cell-attached aminopeptidase activity was predominant in more saline waters (i.e. 15.4%). Changes in substrate structure and availability, strongly related to salinity, might (i) modify patterns of both aminopeptidase activities (free and cell-associated enzymes) and (ii) obligate the prokaryotic communities to modulate rapidly their aminopeptidase activity according to the nutritive conditions available along the gradient

Temporal patterns of phytoplankton assemblages, size spectra and diversity during the wane of a Phaeocystis globosa spring bloom in hydrologically contrasted coastal waters

International audienc

Target 2035-update on the quest for a probe for every protein

Twenty years after the publication of the first draft of the human genome, our knowledge of the human proteome is still fragmented. The challenge of translating the wealth of new knowledge from genomics into new medicines is that proteins, and not genes, are the primary executers of biological function. Therefore, much of how biology works in health and disease must be understood through the lens of protein function. Accordingly, a subset of human proteins has been at the heart of research interests of scientists over the centuries, and we have accumulated varying degrees of knowledge about approximately 65% of the human proteome. Nevertheless, a large proportion of proteins in the human proteome (∼35%) remains uncharacterized, and less than 5% of the human proteome has been successfully targeted for drug discovery. This highlights the profound disconnect between our abilities to obtain genetic information and subsequent development of effective medicines. Target 2035 is an international federation of biomedical scientists from the public and private sectors, which aims to address this gap by developing and applying new technologies to create by year 2035 chemogenomic libraries, chemical probes, and/or biological probes for the entire human proteome

Antoine Furetière, La Nouvelle allégorique, ou histoire des derniers troubles arrivés au royaume d’Eloquence (avec Nicolas Schapira), Toulouse, Société de Littératures Classiques, 2004.

International audienc

Dynamique spatio-temporelle de Phaeocystis globosa en Manche orientale (effets de la turbulence et des apports sporadiques en sels nutritifs)

La variabilité spatio-temporelle de la structure et des processus de surge uptake des communautés phytoplanctoniques de la Manche orientale a été appréhendée au cours d'études réalisées in situ et au laboratoire. Un suivi spatio-temporel, incluant deux sites contrastés d'observation (Baie de Somme et Wimereux) a été réalisé pendant les phases clefs de développement du bloom de P.globosa (mars -:-juillet 2003). Il révèle une grande hétérogénéité spatlo-temporelle de la structure et de la distribution des communautés d'autotrophes liée à la disponibilité des ressources nutritives, elles-mêmes conditionnées. par les paramètres physiques (climat, turbulence) au milieu. La réponse des communautés phytoplanctoniques naturelles à des apports sporadiques en azote fait apparaître une très grande hétérogénénité de réponses dépendant de la structure des assemblages, des périodes et des formes d'azote considérées. Ces approches in situ complétées par des études en conditions contrôlées au laboratoire soulignent l'influence du facteur " turbulence" sur la dynamique de succession des communautés phytoplanctoniques caractéristiques de cet écosystèmeLa variabilité spatio-temporelle de la structure et des processus de surge uptake des communautés phytoplanctoniques de la Manche orientale a été appréhendée au cours d'études réalisées in situ et au laboratoire. Un suivi spatio-temporel, incluant deux sites contrastés d'observation (Baie de Somme et Wimereux) a été réalisé pendant les phases clefs de développement du bloom de P.globosa (mars -:-juillet 2003). Il révèle une grande hétérogénéité spatlo-temporelle de la structure et de la distribution des communautés d'autotrophes liée à la disponibilité des ressources nutritives, elles-mêmes conditionnées. par les paramètres physiques (climat, turbulence) au milieu. La réponse des communautés phytoplanctoniques naturelles à des apports sporadiques en azote fait apparaître une très grande hétérogénénité de réponses dépendant de la structure des assemblages, des périodes et des formes d'azote considérées. Ces approches in situ complétées par des études en conditions contrôlées au laboratoire soulignent l'influence du facteur " turbulence" sur la dynamique de succession des communautés phytoplanctoniques caractéristiques de cet écosystèmeLILLE1-BU (590092102) / SudocSudocFranceF

Dynamics of phytoplankton productivity and exopolysaccharides (EPS and TEP) pools in the Seine Estuary (France, Normandy) over tidal cycles and over two contrasting seasons

Exopolysaccharides (EPS) play an important role in the carbon flux and may be directly linked to phytoplankton and microphytobenthos production, most notably in estuarine systems. However the temporal and spatial dynamics of estuarine EPS are still not well understood, nor how primary productivity triggers this variability at these different scales. The aim of this study was to investigate the primary productivity of phytoplankton and EPS dynamics in the Seine estuary over a tidal cycle in three different haline zones over two contrasted seasons. The other objectives was to investigate the origin of pools of soluble carbohydrates (S-EPS) and transparent exopolymeric particles (TEP) in phytoplankton, microphytobenthos or other compartments. High frequency measurements of productivity were made in winter and summer 2015. Physical and chemical parameters, biomass and EPS were measured at hourly intervals in sub-surface waters and just above the water sediment-interface. Our results confirmed that high frequency measurements improve the accuracy of primary productivity estimations and associated carbon fluxes in estuaries. The photosynthetic parameters were shown to be strongly controlled by salinity and by the concentrations of suspended particle matter at the smallest temporal and at spatial scales. At these scales, our results showed an inverse relationship between EPS concentrations and biomass and productivity, and a positive relationship with sediment resuspension. Additionally, the distribution of EPS appears to be linked to hydrodynamics with the tide at daily scale and with the winter at seasonal scale. At spatial scale, the maximum turbidity zone played an important role in the distribution of TEP. Our results suggest that, in the Seine estuary, between 9% and 33% of the S-EPS pool in the water column can be attributed to phytoplankton excretion, while only 0.4%–1.6% (up to 6.14% in exceptional conditions) originates from the microphytobenthos compartments. Most EPS was attributed to remobilization of detrital carbon pools in the maximum turbidity zone and in the sediment or allochthonous origin

Détection des risques de contamination des Coquilles Saint Jacques en Baie de Seine - DISCCO - Rapport Final

Au cours des trois années d’étude (2013-2015), les concentrations en acide domoïque particulaire (ADp) sont restées inférieures à 60 ng l-1 sur l’ensemble de la zone et aucun dépassement de seuil n’a été observé dans les coquillages au cours de cette même période. Lors de la crise sanitaire de 2012, des concentrations en ADp de plus de 4000 ng l-1 avaient été mesurées au printemps au cours du bloom de Pseudo-nitzschia et des concentrations en AD très élevées avaient rapidement été observées dans les coquilles Saint Jacques dès le début de l’été. Ces observations suggèrent que des concentrations en ADp inférieures à 100 ng l-1 seraient insuffisantes pour une contamination massive des bivalves filtreurs en baie de Seine. Ces résultats sont en accord avec une étude récente qui détermine un risque de toxicité potentielle des coquillages pour des concentrations en ADp > 1000 ng l-1 (McKibben et al., 2015). Par ailleurs, les concentrations en acide domoïque dissout (ADd) mesurées en baie de Seine en 2015 (valeur max=75 ng l-1), plus élevées que celles relevées simultanément dans la phase particulaire soulèvent de nombreuses questions. Ces résultats mettent en évidence la nécessité d’approfondir nos connaissances sur le transfert de l’AD entre les différentes phases (i.e. particulaire et dissout) et entre les différents compartiments (i.e. colonne d’eau, organismes marins et sédiment) afin de mieux appréhender les conséquences de ces efflorescences toxiques sur le fonctionnement et la résilience des écosystèmes côtiers.