Enhanced growth rates of the Mediterranean mussel in a coastal lagoon driven by groundwater inflow

Groundwater discharge is today recognized as an important pathway for freshwater, nutrients and other dissolved chemical substances to coastal systems. While its effect on supporting primary production in coastal ecosystems is increasingly recognized, its impact on growth of animals at higher trophic level (primary and secondary consumers) is less well documented. Here, we investigate the impact of groundwater discharge on the growth of the Mediterranean mussel (Mytilus galloprovincialis) in a coastal lagoon. Growth rates and condition index (tissue weight/shell weight) of mussels growing at groundwater-exposed sites and at a control site in Salses-Leucate lagoon (France) were measured. The mussels in this lagoon produce circadian (daily rhythm) growth increments in their shell, as opposed to semi-diurnal increments in tidally influenced systems. Mussels from groundwater-influenced sites have higher growth rate and condition index compared to those from a control site. Importantly, growth rates from groundwater-influenced sites are amongst the highest rates reported for the Mediterranean region (41 ± 9 μm d⁻¹). The higher growth rates at groundwater-influenced sites are likely a consequence of both the higher winter temperatures of lagoon water as a result of groundwater discharging with relatively constant temperatures, and the groundwater-driven nutrient supply that increase the food availability to support mussel growth. Overall, this study demonstrates that groundwater discharge to Mediterranean lagoons provides favorable environmental conditions for fast growth of mussels of high commercial-quality

The Effect of Captivity on the Dynamics of Active Bacterial Communities Differs Between Two Deep-Sea Coral Species

Microbes play a crucial role in sustaining the coral holobiont’s functions and in particular under the pressure of environmental stressors. The effect of a changing environment on coral health is now a major branch of research that relies heavily on aquarium experiments. However, the effect of captivity on the coral microbiome remains poorly known. Here we show that different cold-water corals species have different microbiome responses to captivity. For both the DNA and the RNA fraction, Madrepora oculata bacterial communities were maintained for at least 6 months of aquarium rearing, while Lophelia pertusa bacteria changed within a day. Interestingly, bacteria from the genus Endozoicomonas, a ubiquitous symbiont of numerous marine hosts, were resilient and remained active in M. oculata for several months. Our results demonstrate that a good knowledge of the coral microbiome and an understanding of the ecological strategy of the holobiont is needed before designing aquarium experiments

Les fluctuations haute fréquence de l'environnement au cours des temps géologiques (mise au point d'un modèle de référence actuel sur l'enregistrement des contrastes saisonniers dans l'Atlantique nord)

La croissance accrétionaire des coquilles de mollusques enregistre l histoire de la vie de ces organismes. L analyse géochimique des coquilles le long d un profil sclérochronologique donne des informations précises sur l évolution des conditions physico-chimiques et environnementales. L observation par cathodoluminescence de coquilles d huîtres Crassostrea gigas a montré que les variations naturelles de l intensité de la luminescence suivaient une cyclicité d ordre saisonnière, lunaire, semi-lunaire et journalière. Ce procédé permet d établir une stratégie de micro-échantillonnage pour l analyse biogéochimique des coquilles. La comparaison des fluctuations haute résolution du 18O et du 13C du crochet avec les données du milieu (température, salinité, chlorophylle a, chimie et isotopie de l eau de mer) a montré qu il est possible d évaluer les contrastes saisonniers de l environnement avec une grande représentativité. La transposition de ce modèle actualiste à des coquilles fossiles a permis de proposer une première estimation de l évolution de la variabilité des températures saisonnières au cours du Cénozoïque dans le Bassin de Paris.PARIS-BIUSJ-Thèses (751052125) / SudocPARIS-BIUSJ-Physique recherche (751052113) / SudocSudocFranceF

Calcein and manganese experiments for marking the shell of the common cockle (

This work focuses on investigating the potential of calcein and manganese as growth markers of the common cockle (Cerastoderma edule) in the bay of Somme (France). Recapture of shells, previously marked using a chemical marking and then bred in natural conditions, was performed in order to determine the shell growth patterns. Calcein marking has shown a fluorescent increment in shells after only 30 min immersion time at 150 mg L-1, but also for shells immersed 3 h at 50 mg L-1. Likewise, manganese shell marking was revealed under cathodoluminescence for shells immersed 1 h at 120 mg L-1 as well as for shells which spent 4 h at 90 mg L-1. A numerical analysis performed on each marked cockles has revealed 23 micro-increments between the mark and the ventral edge of the valves, corresponding to the 23 tides that occurred during the 12 days at liberty post marking. The periodicity of increment formation is thus validated for a tidal frequency. The growth rates of C. edule, ranged from 11.67 to 19.94 μm d-1, decreased significantly with increasing shell length. This preliminary study gives a clue to the understanding of cockle growth and could be used in shellfish production for cockle age monitoring, but also for chemical analysis to learn more about biomineralization process of this species

Tracing Groundwater Sources in Coastal Food Webs: Nitrogen and Carbon Isotope Values in Mussels in a Mediterranean Lagoon

International audienceWhilst the role that groundwater discharge plays in supporting primary production in coastal ecosystems is well recognized, there is still limited evidence on its impacts higher up the food chain. In this study, we investigate the role of groundwater discharge in supplying nitrogen and carbon to the Mediterranean mussels (Mytilus galloprovincialis) in Salses-Leucate lagoon (France). Nitrogen (δ15N) and carbon (δ13C) isotope values in mantle and gill tissues of Mediterranean mussels are used to trace nitrogen and carbon sources at groundwater-exposed sites and a control site. Our results show similar isotope values of mantle and gill tissues, likely due to relatively stable environmental conditions in the study sites and to biochemical composition of tissues. Diet shift, fractionation and the physiological function of tissues could also explain this observation. δ15N values in mussel tissues increase overall in winter at both the groundwater-influenced sites (4.9 to 7.8‰) and the control site (3.4 to 8.5‰) in comparison with those in autumn (3.5 to 7.4‰ at the groundwater-influenced sites and 4.5 to 6.9‰ at the control site), likely due to reduced food supply and slower metabolism in winter, resulting in 15N enrichment. In contrast, mussel δ13C values decrease in winter at the groundwater-influenced sites (-23.4 to -21.6‰) and the control site (-22.0 to -19.0‰), suggesting input of 13C-depleted sources originating from groundwater input. The comparison of the isotopic values of mussel tissues and potential food sources indicates that the main diet of M. galloprovincialis in Salses-Leucate lagoon is a mixture of groundwater particulate organic matter (POM), lagoon POM and marine POM (POM as proxy of phytoplankton). Depleted δ13C values in mussel tissues, particularly at groundwater-exposed sites, provide evidence of uptake of groundwater-derived nutrients. The ecological benefit of groundwater input on filter feeders results thus from local increases in food availability (mainly phytoplankton), supported by groundwater-derived nitrogen and carbon. In summary, this study shows the combined (a) indirect effect of groundwater discharge on mussel growth via uptake of their food, phytoplankton and (b) the likely direct feeding of groundwater POM by M. galloprovincialis. It shows thus the important ecological implication of groundwater inputs in coastal lagoon food webs

Palaeogene climate evolution in the Paris Basin from oxygen stable isotope (δ18O) compositions of marine molluscs

International audienceThe constraint of temperature evolution in coastal environments is an important factor in deciphering the Earth’s global climatic history. In this study, we reconstruct the evolution of sea-surface palaeotemperatures from the oxygen stable isotope compositions in four marine molluscs families in the Paris Basin during the Palaeogene. The combination of several taxa living in different environments is used to limit uncertainties related to the influence of salinity variations on palaeotemperature estimations. One family of bivalves (oysters) and three families of gastropods (Volutidae, Cerithiidae and Turritellidae) were sampled in the French part of the Paris Basin, in Belgium and in the Isle of Wight (southern England). Maximum seawater temperatures were observed during the Early Eocene (c. 30°C), which correspond to the Early Eocene Climatic Optimum, and temperatures then decreased until the Lutetian (c. 20°C). A transient warming, identified as the Middle Eocene Climatic Optimum, occurred during the Bartonian, when temperatures reached 32°C. Temperatures decreased through the Eocene–Oligocene boundary, the coolest interval of the Palaeogene (c. 12°C). A final warming period occurred throughout the Early Oligocene, with temperatures reaching 24°C. The fossils analysed thus record the global climatic intervals of the Palaeogene

Influence of food supply on the à13C signature of mollusc shells: implications for palaeoenvironmental reconstitutions

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36 Growth Patterns of Mediterranean Calcifying Cold-Water Corals

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What do oyster shells tell us about paleoclimatology?

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