Lagoons Of France Research Articles

First detection of Pinna nobilis infection by Haplosporidium pinnae in the sanctuary area of Thau lagoon, France

The noble pen shell Pinna nobilis is an endemic and emblematic giant bivalve whose populations have been recently affected by a mass mortality event (MME), primarily due to the spread of the pathogen Haplosporidium pinnae. Since the beginning of the MME in Spain in 2016, nearly one hundred percent of monitored open sea water populations have been decimated around the Mediterranean Sea. The only refuge areas with living P. nobilis populations were found in coastal lagoons. Today, the Thau lagoon in France is home to a vitally important population of P. nobilis and was thought to be safe from the parasite. Here, we report the first molecular detection of H. pinnae (isolate PN1) in tissue samples of moribund individuals from Thau lagoon.

Assessment of the distribution of Ruditapes spp. in northern Mediterranean sites using morphological and genetic data

ABSTRACT In the 1970s, Ruditapes philippinarum was introduced to France at Arcachon Bay for aquaculture. At present, in Europe, R. philippinarum is often found in place of the native species Ruditapes decussatus. The aim of this study is to evaluate the distribution of these two species along the northern Mediterranean coastline using morphological and morphometric analysis. The sampling period was between June and December 2018. Among the 11 French sites, only 2 contained R. philippinarum, whereas only the indigenous species was present at the other sites. Genetic analyses were used to confirm species identity and to confirm this distribution. A site in Italy, Pialassa Baiona, was also added to the sample. This analysis of Ruditapes from multiple French sites and one Italian site highlights species-level differences in shell morphology between R. decussatus and R. philippinarum. The intraspecific morphometric analysis showed the presence of different groups depending on spatial scales (i.e. at the large scale, between the Mediterranean Sea and the Atlantic, and on the small scale, that is within the Berre lagoon in France. No relationship between morphometric and genetic variation was found. This suggests that the differences in the shell shape of Ruditapes are driven by local environmental conditions.

Plateaus, rebounds and the effects of individual behaviours in epidemics

Plateaus and rebounds of various epidemiological indicators are widely reported in Covid-19 pandemics studies but have not been explained so far. Here, we address this problem and explain the appearance of these patterns. We start with an empirical study of an original dataset obtained from highly precise measurements of SARS-CoV-2 concentration in wastewater over nine months in several treatment plants around the Thau lagoon in France. Among various features, we observe that the concentration displays plateaus at different dates in various locations but at the same level. In order to understand these facts, we introduce a new mathematical model that takes into account the heterogeneity and the natural variability of individual behaviours. Our model shows that the distribution of risky behaviours appears as the key ingredient for understanding the observed temporal patterns of epidemics.

Recruitment of the Pacific oyster Crassostrea gigas in a shellfish-exploited Mediterranean lagoon: discovery, driving factors and a favorable environmental window

In the context of increasing demand for environmental recovery, aquatic systems may face the challenge of evolving under oligotrophication. This is the case in Mediterranean lagoons, in particular the shellfish-farmed Thau lagoon in France, where we studied recruitment of the Pacific oyster Crassostrea gigas. Oyster spat and environmental parameters were monitored at several sampling sites for 3 yr (2012 to 2014) using an original method with a temporal overlap deployment of collectors to study pre- and post-settlement processes and to identify the best conditions for recruitment. Contrary to the ‘no Pacific oyster reproduction’ paradigm in Mediterranean lagoons, our study showed that recruitment of this introduced species is possible in the Thau lagoon at levels comparable to those in other traditional French breeding basins. We identified a favorable environmental window for recruitment characterized by high water temperature ( 26.5°C) and high nanophytoplankton and Chaetoceros spp. abundances ( 4.3 × 106 and 345 × 103 cells l-1, respectively). In these favorable conditions, we hypothesize that the ecosystem functions as an autotrophic system, in contrast to the heterotrophic system that characterizes unfavorable conditions. Under heterotrophic conditions, high abundances of mixotrophic and heterotrophic organisms (ciliates and dinoflagellates) limited the metamorphosis of C. gigas larvae, leading to poor recruitment. This study provides new knowledge on the reproduction of the Pacific oyster in a Mediterranean lagoon under warming and oligotrophication. The shellfish industry will profit from the discovery of spatfields to develop new nursery practices that are eco-friendly and limit risks of transfers with other spatfall areas.

Mobility and fluxes of trace elements and nutrients at the sediment–water interface of a lagoon under contrasting water column oxygenation conditions

The early diagenesis of the major carrier phases (Fe and Mn minerals), trace elements (As, Co, Cr, Hg, MeHg, Ni) and nutrients (ΣNO3, NH4+, ΣPO4) and their exchange at the sediment water/interface were studied in the Berre Lagoon, a Mediterranean lagoon in France, at one site under two contrasting oxygenation conditions (strictly anoxic and slightly oxic) and at an adjacent site with perennially well-oxygenated water. From the concentration profiles of the primary biogeochemical constituents and trace elements of the pore and bottom waters, as well as the total and reactive particulate phases, it was possible to locate and identify the diagenetic reactions controlling the mobility of trace elements in the sediments and quantify their rates by coupling one-dimensional steady-state transport-reaction modelling and thermodynamic speciation calculations.Under oxic conditions and in the absence of benthic organisms, the main redox reactions were well identified vertically in the surface sediments and followed the theoretical sequence of oxidant consumption: O2>ΣNO3/MnO2>Fe(OH)3>SO42-. However, under anoxic conditions, only MnO2, Fe(OH)3 and SO42- reduction were present, and they all occurred at the interface. The main biogeochemical controls on the mobility of As, Cr, Hg, MeHg and Ni in the surface sediments were identified as the adsorption/desorption on and/or coprecipitation/codissolution with Fe oxy-hydroxides. In contrast, Co mobility was primarily controlled by its reactivity towards Mn oxy-hydroxides. In sulphidic sediments, As, Hg and MeHg were sequestered along with Fe sulphides, whereas Co and Ni precipitated directly as metallic sulphides and Cr mobility was enhanced by complexation with dissolved organic ligands. The fluxes of trace elements at the sediment–water interface are essentially dependent on the localisation of their remobilisation and immobilisation reactions under the interface, which in turn is governed by the benthic water oxygenation conditions and kinetic competition among those reaction and diffusion processes. Under oxic conditions, the precipitation of Fe or Mn oxy-hydroxides in the surface sediments constitutes the most efficient mechanism to sequester most of the trace elements studied, thus preventing their diffusion to the water column. Under anoxic conditions the export of trace elements to the water column is dependent on the kinetic competition during the reductive dissolution of Fe and/or Mn oxy-hydroxides, diffusion and immobilisation with sulphides. It is also shown that benthic organisms in the perennially oxygenated site have a clear impact on this general pattern. Based on the extensive dataset and geochemical modelling, it is predicted that the planned re-oxygenation of the entire lagoon basin, if complete, will most likely limit or reduce the export of the trace elements from the sediments to the water column and therefore, limit the impact of the contaminated sediment.

Growth and Condition of the Pacific OysterCrassostrea gigasat Three Environmentally Distinct South African Oyster Farms

The Pacific oyster Crassostrea gigas is cultured at 8 commercial farms in South Africa. Worldwide, environmental-specific intensive selection on the species optimizes commercially beneficial traits, but its performance has not been studied in South Africa. From May 2010 to March 2011, we compared 2-mo measurements of growth rate, condition, and survival of 3 cohorts of different origin in longline culture at 3 different South African environments: 2 sea-based farms located in Saldanha Bay (Western Cape) and Algoa Bay (Eastern Cape) and a land-based farm at Kleinzee (Northern Cape). Overall, Saldanha Bay was cooler (mean sea surface temperature of 16.0°C; CV, 16.2%) than the other 2 localities, which did not differ significantly from one another (Kleinzee: 18.6°C; CV, 20.4%; Algoa Bay: 17.8°C; CV, 8.9%). The high variability at Kleinzee reflected stronger summer warming than at the other 2 farms. Saldanha Bay had higher phytoplankton biomass (mean, 14.3 mg chlorophyll a/m3; CV, 54.2%; May 2010 to March 2011) than did Algoa Bay (mean, 5.3 mg chlorophyll a/m3; CV, 81.0%; September 2010 to March 2011). The 3 cohorts showed similar trends in growth and condition. Growth rates, expressed as live or dry mass gains, were 2–10 times those reported elsewhere in the world, and dry weight condition indices were also high. High live mass growth rates in Algoa Bay, despite its relatively low phytoplankton biomass, seem to reflect a similar phenomenon to that reported in other relatively phytoplankton-poor grow-out environments, such as the Mediterranean Thau Lagoon in France. Dry meat mass gain and condition were highest for oysters in Saldanha Bay, with high food availability offsetting the thermal advantages of the warmer Algoa Bay site. Oysters in the bottom layers of the cages grew significantly faster than those in the top layers, particularly in Saldanha Bay, possibly reflecting fine-scale vertical differences in phytoplankton biomass. Saldanha Bay is the best of the 3 locations to produce market-ready oysters. Algoa Bay yields faster growth but leaner oysters and is a good nursery location, as is Kleinzee, which yields overall slow growth but good shell quality in winter and early spring.