Does Ocean Acidification Benefit Seagrasses in a Mesohaline Environment? A Mesocosm Experiment in the Northern Gulf of Mexico

Ocean acidification is thought to benefit seagrasses because of increased carbon dioxide (CO2) availability for photosynthesis. However, in order to truly assess ecological responses, effects of ocean acidification need to be investigated in a variety of coastal environments. We tested the hypothesis that ocean acidification would benefit seagrasses in the northern Gulf of Mexico, where the seagrasses Halodule wrightii and Ruppia maritima coexist in a fluctuating environment. To evaluate if benefits of ocean acidification could alter seagrass bed composition, cores of H. wrightii and R. maritima were placed alone or in combination into aquaria and maintained in an outdoor mesocosm. Half of the aquaria were exposed to either ambient (mean pH of 8.1 ± 0.04 SD on total scale) or high CO2 (mean pH 7.7 ± 0.05 SD on total scale) conditions. After 54 days of experimental exposure, the δ13C values were significantly lower in seagrass tissue in the high CO2 condition. This integration of a different carbon source (either: preferential use of CO2, gas from cylinder, or both) indicates that plants were not solely relying on stored energy reserves for growth. Yet, after 41 to 54 days, seagrass morphology, biomass, photo-physiology, metabolism, and carbon and nitrogen content in the high CO2 condition did not differ from those at ambient. There was also no indication of differences in traits between the homospecific or heterospecific beds. Findings support two plausible conclusions: (1) these seagrasses rely heavily on bicarbonate use and growth will not be stimulated by near future acidification conditions or (2) the mesohaline environment limited the beneficial impacts of increased CO2 availability

Ocean acidification affects calcareous tube growth in adults and reared offspring of serpulid polychaetes

The energetically costly transition from free-swimming larvae to benthic life stage and maintenance of a calcareous structure can make calcifying marine invertebrates vulnerable to ocean acidification. The first goal of this study was to evaluate the impacts of ocean acidification on calcified tube growth for two Serpulidae polychaete worms. Spirorbis sp. and Spirobranchus triqueter were collected at 11 m depth from the Northwest Mediterranean Sea and maintained for 30 and 90 d, at three mean pHT levels (total scale) of 8.1 (ambient), 7.7, and 7.4. Moderately decreased tube elongation rates were observed in both species at a pHT of 7.7 while severe reductions occurred at pHT 7.4. There was visual evidence of dissolution and tubes were more fragile at lower pH but, fragility was not attributed to changes in fracture toughness. Instead, it appeared to be due to the presence of larger alveoli covered in a thinner calcareous layer. The second objective of the study was to test for effects in offspring development of the species S. triqueter. Spawning was induced, and offspring were reared in the same pH conditions the parents experienced. Trochophore size was reduced at the lowest pH level but settlement success was similar across pH conditions. Post-settlement tube growth was most affected. At 38 d post-settlement, juvenile tubes at pHT of 7.7 and 7.4 were half the size of those at pHT 8.1. Results suggest future carbonate chemistry will negatively affect initiation and persistence of both biofouling and epiphytic polychaete tube worms

Productivity of mixed kelp communities in an Arctic fjord exhibit tolerance to a future climate

Arctic fjords are considered to be one of the ecosystems changing most rapidly in response to climate change. In the Svalbard archipelago, fjords are experiencing a shift in environmental conditions due to the Atlantification of Arctic waters and the retreat of sea-terminating glaciers. These environmental changes are predicted to facilitate expansion of large, brown macroalgae, into new ice-free regions. The potential resilience of macroalgal benthic communities in these fjord systems will depend on their response to combined pressures from freshening due to glacial melt, exposure to warmer waters, and increased turbidity from meltwater runoff which reduces light penetration. Current predictions, however, have a limited ability to elucidate the future impacts of multiple-drivers on macroalgal communities with respect to ecosystem function and biogeochemical cycling in Arctic fjords. To assess the impact of these combined future environmental changes on benthic productivity and resilience, we conducted a two-month mesocosm experiment exposing mixed kelp communities to three future conditions comprising increased temperature (+ 3.3 and + 5.3°C), seawater freshening by ∼ 3.0 and ∼ 5.0 units (i.e., salinity of 30 and 28, respectively), and decreased photosynthetically active radiation (PAR, - 25 and - 40 %). Exposure to these combined treatments resulted in non-significant differences in short-term productivity, and a tolerance of the photosynthetic capacity across the treatment conditions. We present the first robust estimates of mixed kelp community production in Kongsfjorden and place a median compensation irradiance of ∼12.5 mmol photons m−2 h−1 as the threshold for positive net community productivity. These results are discussed in the context of ecosystem productivity and biological tolerance of kelp communities in future Arctic fjord systems

Tall tales from de Sitter space II: Field theory dualities

We consider the evolution of massive scalar fields in (asymptotically) de Sitter spacetimes of arbitrary dimension. Through the proposed dS/CFT correspondence, our analysis points to the existence of new nonlocal dualities for the Euclidean conformal field theory. A massless conformally coupled scalar field provides an example where the analysis is easily explicitly extended to 'tall' background spacetimes.Comment: 31 pages, 2 figure

Effect of Carbonate Chemistry Alteration on the Early Embryonic Development of the Pacific Oyster (Crassostrea gigas)

Ocean acidification, due to anthropogenic CO2 absorption by the ocean, may have profound impacts on marine biota. Calcareous organisms are expected to be particularly sensitive due to the decreasing availability of carbonate ions driven by decreasing pH levels. Recently, some studies focused on the early life stages of mollusks that are supposedly more sensitive to environmental disturbances than adult stages. Although these studies have shown decreased growth rates and increased proportions of abnormal development under low pH conditions, they did not allow attribution to pH induced changes in physiology or changes due to a decrease in aragonite saturation state. This study aims to assess the impact of several carbonate-system perturbations on the growth of Pacific oyster (Crassostrea gigas) larvae during the first 3 days of development (until shelled D-veliger larvae). Seawater with five different chemistries was obtained by separately manipulating pH, total alkalinity and aragonite saturation state (calcium addition). Results showed that the developmental success and growth rates were not directly affected by changes in pH or aragonite saturation state but were highly correlated with the availability of carbonate ions. In contrast to previous studies, both developmental success into viable D-shaped larvae and growth rates were not significantly altered as long as carbonate ion concentrations were above aragonite saturation levels, but they strongly decreased below saturation levels. These results suggest that the mechanisms used by these organisms to regulate calcification rates are not efficient enough to compensate for the low availability of carbonate ions under corrosive conditions

Impact des changements environnementaux sur les organismes et communautés benthiques et pélagiques

Since my CNRS integration in 2009, my research activities have revolved around two main research themes: 1) the impact of environmental changes on bivalves of commercial interest and 2) the environmental control of planktonic and benthic communities in the Mediterranean Sea. My work on bivalves has been innovative in several respects (original experimental approach, long-term experiment, consideration of several factors of environmental change, effort to synthesize existing studies) and place me among the international experts on this theme of research. Studying the response of planktonic and benthic communities to changes in the environment provided an opportunity to develop various experimental tools used either directly in the natural environment or at proximity in mobile containers. These tools have enabled me to conduct and promote research in collaboration with many international colleagues and the recent developments provided me with an important technological base for the rest of my career. In the future, a significant part of my research activity will take place within the framework of the CocoriCO2 project aimed at estimating the future of shellfish farming on the French coast. Following this project focused mainly on the assessment of the sensitivity of ecosystems (observation) and the sensitivity of species (experimental) to environmental changes, I aim to test different remediation techniques to limit the effects of acidification. on bivalve molluscs. I would like to continue my research effort on the environmental control of the functioning of planktonic and benthic communities through ongoing research projects, submitted or under consideration. I propose a multi-factorial approach based on a combination of different experimental techniques.Depuis mon intégration au CNRS en 2009, mes activités de recherche se sont articulées autour de deux principales thématiques de recherche : 1) l’impact des changements environnementaux sur les bivalves d’intérêt commercial et 2) le contrôle environnemental des communautés planctoniques et benthiques en Mer Méditerranée. Mes travaux sur les bivalves ont été novateurs à plusieurs égards (approche expérimentale originale, expérience sur le long-terme, prise en compte de plusieurs facteurs du changement environnemental, effort de synthèse des études existantes) et me placent parmi les experts internationaux sur cette thématique de recherche. L'étude de la réponse des communautés planctoniques et benthiques aux modifications du milieu a été l'occasion de développer divers outils expérimentaux utilisés que ce soit directement dans le milieu naturel ou à proximité de celui-ci dans des containers aménagés. Ces outils m'ont permis de mener et valoriser des recherches en collaboration avec de nombreux collègues internationaux et les récents développements opérés m'assurent un socle technologique important pour la suite de ma carrière. À l'avenir, une part importante de mon activité de recherche se déroulera dans le cadre du projet CocoriCO2 (FEAMP) visant à estimer le devenir de la conchyliculture sur le littoral français. À la suite de ce projet axé principalement sur l'évaluation de la sensibilité des écosystèmes (observation) et de la sensibilité des espèces (expérimental) aux changements environnementaux, j'ambitionne de tester différentes techniques de remédiation pour limiter les effets de l'acidification sur les mollusques bivalves. Je souhaite poursuivre mon effort de recherche sur le contrôle environnemental du fonctionnement des communautés planctoniques et benthiques par le biais de projets de recherche en cours, soumis ou en réflexion. Je propose une approche multi-factorielle basée sur une combinaison de différentes techniques expérimentales

Métabolisme des écosystemes côtiers : de l'échelle locale (fjord de Randers, baie de Palma et estuaire de l'Escaut) à l'échelle européenne

The coastal zone, the transition area between land and the open ocean, receives considerable amounts of freshwater, nutrients as well as dissolved and particulate organic matter. These inputs make the coastal zone a very biogeochemically active area. The trophic status of the coastal zone, that is whether it is autotrophic or heterotrophic, is still a matter of debate. The present work had three main objectives: (1) to compile and analyse a bibliographic database of benthic and planktonic primary production (GPP) and community respiration (CR) measured by incubation methods and by the Land-Ocean Interaction in the Coastal Zone (LOICZ) budgeting approach in the European coastal zone, (2) to test different methods to estimate the functioning of three European coastal sites (Randers Fjord, Palma Bay and Scheldt Estuary). These methods are the classical O2 incubation technique, the LOICZ budgeting procedure and other open-system techniques such as the Response Surface Difference (RSD) method and daily cycles of dissolved inorganic carbon (DIC) and O2. Moreover, as the estimation of the gas exchange coefficient of the air-sea interface (k) is critical when applying open-system methods, this parameter and its relationship with wind speed were studied in two of the sites (Randers Fjord and Scheldt estuary) and (3) to study how the metabolic parameters such as GPP or CR both in the benthic and planktonic compartment are controlled by environmental conditions. More than 190 papers have been analysed among which 129 were integrated in a database available on the Internet (http://www.obs-vlfr.fr/eurotroph/index.php). The analysis of the bibliographic database allowed pinpointing a severe lack of knowledge in many areas of Europe such as the Eastern Mediterranean Sea, the Northern Baltic Sea and the Northern North Sea. An assessment of the net ecosystem production (NEP = GPP + CR) of the European coastal zone was not possible based on this study. Indeed, several confident estimates of parameters such as the mineralization of organic matter in the water column, the decrease of benthic production and respiration with depth and the distribution of macrophytes are lacking. The different methods tested during this study generally provided consistent results although each of these is associated with significant errors and uncertainties which limit their use to specific sites and conditions. Particularly, the LOICZ procedure applied to dissolved inorganic phosphorus (DIP) failed to provide a realistic estimate of the trophic status in the Scheldt estuary. This is due to a strong impact of abiotic processes such a sorption and desorption to and from suspended matter and sediments of the non-conservative DIP flux in this highly turbid system. Open-system methods suffer from the difficulty to estimate with accuracy the gas exchange coefficient. Although the relation linking this parameter to the wind speed was shown to be site-specific, the validation of this relationship in the Scheldt estuary using the LOICZ approach applied to DIC was not possible due to strong associated errors and uncertainties. Finally, significant differences observed between GPP and CR estimated by incubation and open-system methods confirmed previous results and suggest that future works should focus on this matter. The three sites investigated were well contrasted: from the nutrient-rich and turbid Scheldt estuary to the oligotrophic seagrass-dominated Bay of Palma. The metabolic parameters were well related to these environmental differences. Indeed, the highest CR rates were measured in the Scheldt estuary while GPP was strongly limited by light availability. The highest GPP was measured in the Randers Fjord where nutrient concentrations as well as water column stratification and a relatively low turbidity allowed the riverine phytoplankton to remain very active in the estuarine zone. While the Scheldt estuary was clearly the most heterotrophic site in this study, it was not possible to conclude whether the Randers Fjord or the Bay of Palma is the most productive ecosystem on an annual scale

Shellfish farming in a high-CO2 world

International audienc

Métabolisme des écosystèmes côtiers : de l'échelle locale (fjord de Randers, baie de Palma et estuaire de l'Escaut) à l'échelle européenne

The coastal zone, the transition area between land and the open ocean, receives considerable amounts of freshwater, nutrients as well as dissolved and particulate organic matter. These inputs make the coastal zone a very biogeochemically active area. The trophic status of the coastal zone, that is whether it is autotrophic or heterotrophic, is still a matter of debate. The present work had three main objectives: (1) to compile and analyse a bibliographic database of benthic and planktonic primary production (GPP) and community respiration (CR) measured by incubation methods and by the Land-Ocean Interaction in the Coastal Zone (LOICZ) budgeting approach in the European coastal zone, (2) to test different methods to estimate the functioning of three European coastal sites (Randers Fjord, Palma Bay and Scheldt Estuary). These methods are the classical O2 incubation technique, the LOICZ budgeting procedure and other open-system techniques such as the Response Surface Difference (RSD) method and daily cycles of dissolved inorganic carbon (DIC) and O2. Moreover, as the estimation of the gas exchange coefficient at the air-sea interface (k) is critical when applying open-system methods, this parameter and its relationship with wind speed were studied in two of the sites (Randers Fjord and Scheldt estuary) and (3) to study how the metabolic parameters such as GPP or CR both in the benthic and planktonic compartment are controlled by environmental conditions.More than 190 papers have been analysed among which 129 were integrated in a database available on the Internet (http://www.obs-vlfr.fr/eurotroph/index.php). The analysis of the bibliographic database allowed pinpointing a severe lack of knowledge in many areas of Europe such as the Eastern Mediterranean Sea, the Northern Baltic Sea and the Northern North Sea. An assessment of the net ecosystem production (NEP = GPP + CR) of the European coastal zone was not possible based on this study. Indeed, several confident estimates of parameters such as the mineralization of organic matter in the water column, the decrease of benthic production and respiration with depth and the distribution of macrophytes are lacking.The different methods tested during this study generally provided consistent results although each of these is associated with significant errors and uncertainties which limit their use to specific sites and conditions. Particularly, the LOICZ procedure applied to dissolved inorganic phosphorus (DIP) failed to provide a realistic estimate of the trophic status in the Scheldt estuary. This is due to a strong impact of abiotic processes such a sorption and desorption to and from suspended matter and sediments on the non-conservative DIP flux in this highly turbid system. Open-system methods suffer from the difficulty to estimate with accuracy the gas exchange coefficient. Although the relation linking this parameter to the wind speed was shown to be site-specific, the validation of thisμ relationship in the Scheldt estuary using the LOICZ approach applied to DIC was not possible due to strong associated errors and uncertainties. Finally, significant differences observed between GPP and CR estimated by incubation and open-system methods confirmed previous results and suggest that future works should focus on this matter.The three sites investigated were well contrasted: from the nutrient-rich and turbid Scheldt estuary to the oligotrophic seagrass-dominated Bay of Palma. The metabolic parameters were well related to these environmental differences. Indeed, the highest CR rates were measured in the Scheldt estuary while GPP was strongly limited by light availability. The highest GPP was measured in the Randers Fjord where nutrient concentrations as well as water column stratification and a relatively low turbidity allowed the riverine phytoplankton to remain very active in the estuarine zone. While the Scheldt estuary was clearly the most heterotrophic site in this study, it was not possible to conclude whether the Randers Fjord or the Bay of Palma is the most productive ecosystem on an annual scale.L'océan côtier, la zone de transition entre le continent et l'océan ouvert, reçoit des apports considérables d'eau douce, de sels nutritifs ainsi que de matière organique dissoute et particulaire en provenance du continent. Ces apports font que la zone côtière est une région très active du point de vue biogéochimique. Le statut trophique de l'océan côtier, distinction entre l'autotrophie et l'hétérotrophie) est un sujet encore très discuté. L'étude présentée ici a trois objectifs: (1) de compiler et analyser une base de données bibliographique concernant la production primaire brute (GPP) et la respiration communautaire (CR) benthiques et planctoniques, mesurées par des incubations et par l'approche budgétaire Land-Ocean Interaction in the Coastal Zone (LOICZ) au niveau de la zone côtière européenne. (2) de tester différentes méthodes d'estimation du métabolisme de trois sites côtiers européens. Ces méthodes sont la méthode classique d'incubations O2, la méthode LOICZ et d'autres méthodes en système ouvert telles que la méthode Response Surface Difference (RSD) et l'utilisation de cycles journaliers de carbone inorganique dissous et d'O2. De plus, étant donné que l'estimation du coefficient d'échange de gaz à l'interface air-mer (k) est critique lors de l'utilisation de méthodes en système ouvert, ce paramètre et sa relation avec la vitesse du vent ont été étudiés dans deux des sites (Fjord de Randers et estuaire de l'Escaut). (3) d'étudier la relation existant entre les paramètres métaboliques tels que GPP ou CR dans les compartiments benthiques et planctoniques.Plus de 190 publications ont été analysées dont 129 ont été intégrées à une base de données consultable sur Internet (http://www.obs-vlfr.fr/eurotroph/index.php). L'analyse de cette base de données a permis de mettre en avant un sévère manque mesures dans de nombreuses régions telles que le bassin Est de la mer Méditerranée, le nord de la Baltique et le nord de la mer du Nord. Une estimation de la production nette (NEP = GPP+ CR) de la zone côtière européenne n'a pas été possible dans cette étude. En effet, des estimations fiables de paramètres tels que la minéralisation de matière organique dans la colonne d'eau, la diminution de la production et respiration benthique avec la profondeur et la distribution des macrophytes, font cruellement défaut.Les différentes méthodes testées ont fourni des résultats le plus souvent similaires, bien que chacune d'elles soit associée à une marge d'erreur significative qui limite son utilisation à des sites et conditions bien particuliers. La méthode LOICZ basée sur le phosphore inorganique dissous (DIP) n'a pu fournir un résultat réaliste dans l'estuaire de l'Escaut. Ceci est dû à un fort impact de processus abiotiques sur le flux non-conservatif de DIP, tels que l'adsorption/désorption sur ou à partir de particules en suspension et/ou du sédiment, dans ce système très turbide. Les méthodes en milieu ouvert souffrent de la difficulté d'estimer de façon fiable le coefficient d'échange de gaz à l'interface air-mer (O2 ou CO2). Bien qu'il ait été montré que la relation liant ce paramètre à la vitesse du vent dépendait du site étudié, la relation établie pour l'estuaire de l'Escaut n'a pu être validée en utilisant la méthode LOICZ appliquée au DIC en raison des fortes erreurs associées. Finalement, les différences significatives observées entre les estimations de GPP et CR à partir des incubations et des méthodes en système ouvert confirment les résultats de travaux antérieurs et mériteraient une attention particulière à l'avenir.Les trois sites étudiés sont bien contrastés: du turbide et eutrophisé estuaire de l'Escaut à la baie oligotrophe dominée par les macrophyte (Palma). De relations significatives entre les paramètres métaboliques et les conditions environnementales ont été montrées. En effet, les plus fortes CR ont été mesurées dans l'Escaut tandis que la GPP y était très sévèrement limitée par la disponibilité en lumière. Les plus fortes GPP ont été mesurées dans le fjord de Randers où les concentrations en sels nutritifs ainsi que la stratification de la colonne d'eau et la faible turbidité permettent au phytoplancton en provenance de la rivière de continuer à produire dans la zone estuarienne. Tandis que l'estuaire de l'Escaut est clairement le site le plus hétérotrophe, il a été impossible de différencier les métabolismes de la baie de Palma et du fjord de Randers sur une échelle annuelle