Introduction While crucial to ensuring the production of accurate and high-quality data—and to avoid erroneous conclusions—data quality control (QC) in environmental monitoring datasets is still poorly documented. Methods With a focus on annual inter-laboratory comparison (ILC) exercises performed in the context of the French coastal monitoring SOMLIT network, we share here a pragmatic approach to QC, which allows the calculation of systematic and random errors, measurement uncertainty, and individual performance. After an overview of the different QC actions applied to fulfill requirements for quality and competence, we report equipment, accommodation, design of the ILC exercises, and statistical methodology specially adapted to small environmental networks (<20 laboratories) and multivariate datasets. Finally, the expanded uncertainty of measurement for 20 environmental variables routinely measured by SOMLIT from discrete sampling—including Essential Ocean Variables—is provided. Results, Discussion, Conclusion The examination of the temporal variations (2001–2021) in the repeatability, reproducibility, and trueness of the SOMLIT network over time confirms the essential role of ILC exercises as a tool for the continuous improvement of data quality in environmental monitoring datasets.

The effect of environmental change in structuring the phytoplankton communities of the coastal waters of the Eastern English Channel was investigated by applying a trait-based approach on two decades (1996-2019) of monitoring on diatoms and Phaeocystis. We show that phytoplankton species richness in an unbalanced nutrient supply context was influenced by wind-driven processes, ecological specialization for dissolved inorganic phosphorous, temporal niche differentiation, and a competition-defense and/or a growth-defense trade-off, a coexistence mechanism where weak competitors (i.e., slower growing) are better protected against predation. Under the influence of both environmental perturbations (e.g., wind-driven processes, freshwater influence, unbalanced nutrient levels) and biotic interactions (e.g., competition, predation, facilitation), phytoplankton species exhibited specific survival strategies such as investment on growth, adaptation and tolerance of species to environmental stresses, silicification and resource specialization. These strategies have led to more speciose communities, higher productivity, functional redundancy and stability in the last decade. Our results revealed that the unbalanced nutrient reduction facilitated Phaeocystis blooms and that anthropogenic climate warming and nitrate reduction may threaten the diatom communities of the eastern English Channel in a near future. Our results provide strong support for biogeographical historical and niche-based processes in structuring the phytoplankton community in this temperate region. The variety of species responses that we characterized in this region may help to better understand future changes in pelagic ecosystems, and can serve as a basis to consider functional approaches for future ecosystem management.

Although eutrophication induced by anthropogenic nutrient enrichment is a driver of shifts in community composition and eventually a threat to marine biodiversity, the causes and consequences on ecosystem functioning remain greatly unknown. In this study, by applying a trait-based approach and measuring niche breadth of diatoms and copepods, the drivers and underlying mechanisms of the seasonal species succession of these ecological communities in a coastal system dominated in spring by Phaeocystis blooms were explored. It is suggested that the seasonal succession of diatoms and copepods is the result of several trade-offs among functional traits that are controlled by the seasonal abiotic and biotic pressure encountered by the plankton communities. The results of this study highlight that a trade-off between competition and predator, i.e., weak competitors are better protected against predation, plays an important role in promoting plankton species richness and triggers the Phaeocystis bloom. As often observed in eutrophicated ecosystems, only the biotic homogenization of the copepod community and the shift in the diet of copepods toward Phaeocystis detrital materials have been detected during the Phaeocystis bloom. The diatom and copepod communities respond synchronously to fluctuating resources and biotic conditions by successively selecting species with specific traits. This study confirms the key role of competition and predation in controlling annual plankton succession.

At the interface between terrestrial and marine biomes, estuaries display high ecological productivity and provide goods and services to humans. Associated with many ecological functions, they are nursery, refuge, and growing areas for many species fish. These ecological functions and services depend on both their ecological production and trophic carrying capacity and the durability of food web functioning. These transitional key habitats undergo both strong anthropogenic pressures and climatic influences that impact the structure and dynamics of estuarine biodiversity. In this context, we explore, here, three decades of the Gironde estuary ecosystem history to detect the food web’s response to global changes-induced effect on biodiversity. At least two Ecological Abrupt Shifts associated with deep modifications in the biodiversity at most trophic levels have been documented for this particular ecosystem. Three food web models were thus calibrated, one for each of the three periods discriminated by the two shifts that occurred at the end of the 1980s and the beginning of the 2000s. Results highlighted that the ecotrophic efficiency estimate for subtidal macrofauna and shrimps reached the maximum possible values during the last period. This could mean that the Gironde estuary fully reached its trophic carrying capacity due to a food limitation especially for benthos demersal fish. We also observed a significant decrease in some food web indicators (such as Average Mutual Information, System Omnivory Index, and Average Path Length) usually associated with ecosystem stress, suggesting a significant impact of global change on the Gironde estuary ecosystem health and questioning the sustainability of the ecological functions associated with this ecosystem.

While long-term monitoring is essential to improve our knowledge of marine ecosystems health, it remains challenging to summarise complex ecological data in order to characterise and understand biodiversity trends. To compile monitoring data across large numbers of species, scientists and policymakers mainly rely on diversity and species richness indices. This task may prove complicated however, as many indices exist and no individual metric undoubtedly emerges as the best overall. Here, using data from zooplankton surveys from 1998 to 2014, we examined year-to-year changes in copepod communities in two littoral ecosystems of Western Europe - the Arcachon Bay and the Gironde estuary - that share similar climate, but with different local ecological processes, especially hydrological conditions. We tested the ability of commonly used α and β-diversity metrics, such as species richness, Pielou's evenness or Jaccard's index, to mirror year-to-year changes in species abundances and we detected a synchronous change in both copepod abundances and α-diversity that took place circa 2005 in the two sites. In response to changes in environmental conditions such as nutrients, salinity, river discharge or particulate matter, two opposite biodiversity trends were observed, with a decrease in copepod diversity in the Arcachon Bay but an increase in the downstream part of the Gironde estuary. Although diversity metrics allowed us to well detect trends, the use of multivariate approaches such as principal component analysis provided important information on how and why diversity fluctuates. Our study provides evidence that long-term monitoring programmes must be encouraged for optimising management and conservation actions such as the Marine Strategy Framework Directive and that more local comparative studies need to be initiated for better characterising diversity trajectories at very fine scales at which ecologists often work.

Alterations of species phenology in response to climate change are now unquestionable. Until now, most studies have reported precocious occurrence of life cycle events as a major phenological response. Desynchronizations of biotic interactions, in particular predator-prey relationships, are however assumed to strongly impact ecosystems' functioning, as formalized by the Match-Mismatch Hypothesis (MMH). Temporal synchronicity between juvenile fish and zooplankton in estuaries is therefore of essential interest since estuaries are major nursery grounds for many commercial fish species. The Gironde estuary (SW France) has suffered significant alterations over the last three decades, including two Abrupt Ecosystem Shifts (AES), and three contrasted intershift periods. The main objective of this study was to depict modifications in fish and zooplankton phenology among inter-shift periods and discuss the potential effects of the resulting mismatches at a community scale. A flexible Bayesian method was used to estimate and compare yearly patterns of species abundance in the estuary among the three pre-defined periods. Results highlighted (1) an earlier peak of zooplankton production and entrance of fish species in the estuary and (2) a decrease in residence time of both groups in the estuary. Such species-specific phenological changes led to changes in temporal overlap between juvenile fish and their zooplanktonic prey. This situation questions the efficiency and potentially the viability of nursery function of the Gironde estuary, with potential implications for coastal marine fisheries of the Bay of Biscay.

The North Pacific copepod Eurytemora pacifica Sato, 1913 was fortuitously found in a sea water tank of the Marinarium of Concarneau (Southern Brittany, France). The presence of ovigerous females in this tank as well as in some nearby ecosystems confirms the successful introduction of this species along the Atlantic coast of France. Morphology was examined using scanning electron microscopy and confirmed the species identity. The presence of two types of females resulting from cyclomorphosis was confirmed, as well as the production of two types of eggs. The French Atlantic coasts seem to be the only area in the world where the species has been reported as a non-indigenous

Estuarine ecosystems have been described as a mosaic of habitats exhibiting different physical, biological and chemical properties and processes. These habitats are of primary importance for fishes, providing refuges and/or food for juveniles. While it is well known that habitats contribute also to the structuration of meio- and macrobenthic assemblages, this concept of habitat has never been associated to zooplankton communities, a major food resource for many pelagic fishes during summer in North-European estuaries. The objective of this work was thus to assess if estuarine habitats, in addition to the salinity gradient, structured zooplankton communities as well. Sampling was conducted at high tide during summer in a highly turbid system, the Gironde estuary, for which primary production and thus food resource at the basis of the food web is strongly limited. The results showed that even if the upstream-downstream estuarine gradient was the main factor structuring zooplankton at the scale of the estuary, there was a significant difference of zooplankton assemblages between samples collected over subtidal areas and those collected over intertidal areas. More particularly, the estuarine gradient was associated to the distribution pattern of species while difference between subtidal and intertidal samples were mainly due to difference in the level of abundance of species. Stable isotope analysis revealed that these zooplanktonic omnivorous species may be attracted to intertidal mudflats by microphytobenthos availability and that some planktivorous fishes, in particular Alosa fallax, preferentially fed on this zone. The role of intertidal habitats in structuring zooplankton assemblages suggests that this habitat strongly participates to the production of planktivorous species and that it represents a biotic vector of carbon resources toward subtidal areas. The loss of tidal flats habitats could thus have consequences on the functioning of pelagic system as well.

In macrotidal coastal ecosystems, spatial heterogeneity of the water column properties is induced by both oceanic and continental influences. Hydrodynamic processes generate a land-sea gradient of environmental conditions, affecting the biological performances of sedentary organisms. The aim of the present study is to establish an extensive spatial assessment in the reproductive investment of the wild Pacific oyster Crassostrea gigas in Arcachon Bay. This is done by looking for a relationship between the Lawrence and Scott condition index (LSCI) and two tidal processes: the immersion level (IL) and the local oceanic flushing time (LoFt). The LSCI of C. gigas was assessed, just before gamete release, at 68 sampling stations in Arcachon Bay. Oyster performance was overall low and spatially variable. Significant differences in the LSCI were detected between the outer and inner bay. Oyster reefs located toward the mouth of the bay exhibited high LSCI (between 9 and 11), while oyster reefs located in inner bay, especially in south-eastern part around the Eyre River, had low LSCI (below 6). Linear modelling allowed to highlight significant effects of both tidal processes IL and LoFt on the obtained LSCI gradient. IL, LoFt explained 33% of the spatial variability observed on LSCI (IL=3%; LoFt=17%; LoFt+IL: 13%), 6% were attributed to the intra-station variation (ISv). Thus, high IL and rapid LoFt favor a better development of somatic-gonadal volume, probably because of longer feeding time and higher supply of food from the ocean by tide flows. Disentangling the effects of IL and LoFt on LSCI allowed to describe the spatial pattern in 61% of variability not explained by both tidal factors. A residual gradient directed southeast-northwest highlighted that others factors, independent from IL and LoFt seems to hamper inner bay oyster reproductive performance. Consequently, investigating on the ecological functioning (Eyre influences), trophic potential and anthropogenic pressures of this zone seem crucial on the understanding of C. gigas reproductive pattern in Arcachon Bay.

The North Pacific copepod Eurytemora pacifica Sato, 1913 was fortuitously found in a sea water tank of the Marinarium of Concarneau (Southern Brittany, France). The presence of ovigerous females in this tank as well as in some nearby ecosystems confirms the successful introduction of this species along the Atlantic coast of France. Morphology was examined using scanning electron microscopy and confirmed the species identity. The presence of two types of females resulting from cyclomorphosis was confirmed, as well as the production of two types of eggs. The French Atlantic coasts seem to be the only area in the world where the species has been reported as a non-indigenous species (NIS).

The species composition and seasonal abundance patterns of gelatinous zooplankton are poorly known for many European coastal-zone waters. The seasonal abundance and distribution of the dominant species of hydromedusae along a salinity gradient within the Gironde Estuary, Atlantic coast of France, were evaluated based on monthly surveys, June 2013 to April 2014. The results confirmed the presence of three species considered to be introduced in many coastal ecosystems around the world: Nemopsis bachei (Agassiz, 1849), Blackfordia virginica (Mayer, 1910), and Maeotias marginata (Modeer, 1791). These species were found at salinities ranging from 0 to 22.9 and temperatures ranging from 14.5 to 26.6 degrees C, demonstrating their tolerance to a wide range of estuarine environmental conditions. There was a clear succession of the three species that was influenced by temperature and salinity. Blackfordia virginica was the dominant hydromedusae during the warmest months and occurred at very high abundance (up to 634 individuals. m(-3) corresponding to 21.40 g.m(-3) as wet weight). The seasonal evolution of the size distribution indicated an extended period of release of medusae by hydroid polyps, and rapid growth, covering the whole period of occurrence for B. virginica. Nemopsis bachei also was present during the warmer months but only locally common. In contrast, Maeotias marginata only occurred in low numbers during autumn and had not been previously detected in the Gironde Estuary. Non-native jellyfishes clearly represent a prominent component of the Gironde Estuary, and additional work is needed to understand the potential impacts on the structure and functioning of entire zooplankton community.

La preservation de l’estuaire de la Gironde represente un enjeu majeur. En effet, malgre les innovations deployees sur le territoire de Bordeaux Metropole, il fait l’objet de constats alarmants dans un contexte ou les pressions sont croissantes (demographie de l’agglomeration, changement climatique, etc.). Pour repondre aux ambitions de Bordeaux Metropole et l’accompagner dans la reconquete d’un etat ecologique acceptable de l’estuaire, un consortium s’est forme autour du programme Etiage (pour : etude integree de l’effet des apports amont et locaux sur le fonctionnement de la Garonne estuarienne). Il etait compose de laboratoires de recherche et de gestionnaires, afin de croiser reponses scientifiques et resultats operationnels. Ce programme a permis d’expliciter les facteurs responsables de la qualite biogeochimique de la Gironde. Les apports amont et locaux (stations d’epuration (STEP) et deversoirs d’orage (DO)) de macro- et micropolluants (organiques et metalliques) ont ete estimes. De meme, les conditions physico-chimiques (presence du bouchon vaseux, variations saisonnieres de temperature et de debit, etc.) de la Garonne estuarienne et l’impact des apports sur le compartiment biologique ont ete documentes. L’enjeu etait de comprendre les facteurs regissant la qualite de ce milieu recepteur complexe afin de proposer de nouvelles solutions, basees notamment sur la gestion des rejets d’assainissement de l’agglomeration. Les connaissances acquises ont ainsi permis au gestionnaire de l’assainissement de soutenir un plan d’action global qui vise a reduire l’empreinte de la metropole. Celui-ci porte conjointement sur la reduction des flux de micro- et macropolluants. Les micropolluants (metaux et composes organiques) font l’objet d’une demarche de reduction a la source. Les macropolluants sont adresses au travers du deploiement d’outils de diagnostic, de suivi en temps reel (dans le reseau et les milieux) et de modelisation pour progresser vers l’objectif d’une gestion du systeme d’assainissement pilotee par l’aval, basee sur la qualite des effluents et du milieu.

For decades, global climate change has directly and indirectly affected the structure and function of ecosystems. Abrupt changes in biodiversity have been observed in response to linear or sudden modifications to the environment. These abrupt shifts can cause long-term reorganizations within ecosystems, with communities exhibiting new functional responses to environmental factors. Over the last 3 decades, the Gironde estuary in southwest France has experienced 2 abrupt shifts in both the physical and chemical environments and the pelagic community. Rather than describing these shifts and their origins, we focused on the 3 inter-shift periods, describing the structure of the fish community and its relationship with the environment during these periods. We described fish biodiversity using a limited set of descriptors, taking into account both species composition and relative species abundances. Inter-shift ecosystem states were defined based on the relationship between this description and the hydro-physico-chemical variables and climatic indices defining the main features of the environment. This relationship was described using generalized linear mixed models on the entire time series and for each inter-shift period. Our results indicate that (1) the fish community structure has been significantly modified, (2) environmental drivers influencing fish diversity have changed during these 3 periods, and (3) the fish-environment relationships have been modified over time. From this, we conclude a regime shift has occurred in the Gironde estuary. We also highlight that anthropogenic influences have increased, which re-emphasizes the importance of local management in maintaining fish diversity and associated goods and services within the context of climate change.

Resume : Cet article analyse les conditions prealables a la creation d’un observatoire de sciences participatives de la biodiversite sur le Bassin d’Arcachon. L’enquete sociologique revele les tensions entre finalites utilitaristes de recueil de donnees, nouveau mode collaboratif de construction des savoirs, instrument de communication politique, et demarche de vigilance citoyenne ; entre definition concertee de principes d’organisation des dispositifs et controle de positions de pouvoir sur le territoire. Loin du consensus apparent sur la protection de la biodiversite, le positionnement des acteurs du territoire redefinit les enjeux environnementaux, precise les relations sciences - societe et esquisse de nouvelles hierarchies des priorites de gestion. Mots-cles : conceptions controversees des sciences participatives, renouvellement de la gouvernance de la biodiversite, democratie participative, interactions science-societe *** Abstract: This paper considers the social and scientific requirements for a citizen science monitoring programme on biodiversity in Arcachon Bay (France). The sociological study reveals tensions between different conceptions of what a citizen science programme should be: a means for storing oriented-data; a new way to co-create scientific knowledge; a political communication tool; a way to develop citizen stewardship; or a place for expressing activist environmental demands. Citizen science programmes also tend to reveal tensions between participatory governance and classical management of environmental issues. Despite a seeming consensus amongst actors on biodiversity conservation, in practice contests over different citizen science conceptions have the potential to re-define environmental issues, to re-specify relationships between science and society and outline new management priorities. Keywords: contested conceptions of citizen science, biodiversity management renewal, public participation, science society interactions

Global change has become a major driving force of both terrestrial and marine systems. Located at the interface between these two realms, estuarine ecosystems are probably the place where both direct and indirect effects of human activities conspire together to affect biodiversity from phytoplankton to top predators. Among European estuarine systems, the Gironde is the largest estuary of Western Europe and many studies have provided evidence that it has been affected by a variety of anthropogenic stressors such as thermal and chemical pollution, physical alterations and exploitation, especially for maritime traffic. In such a context, species introduction is also a current major issue with the establishment of strong competitive species that could lead to ecosystem reorganization with potential decrease or even disappearance of native species. In the Gironde estuary, this hypothesis was proposed for the invasive shrimp species Palaemon macrodactylus as a decrease in the native species abundance was observed at the same time. Although species introduction often takes place via ballast water, the influence of climate-driven changes on the establishment of new species remains a key issue. The calanoid copepod Acartia tonsa, observed in the Gironde estuary for the first time in 1983, have since colonized most part of the estuary, reaching a level of abundance comparable to the dominant native species Eurytemora affinis. In this study, using both the concept of the ecological niche sensu Hutchinson (fundamental and realized niches) and statistical models, we reveal that the dynamics of the colonization of A. tonsa was facilitated by environmental conditions that have become closer to its environmental optimum with respect to temperature and salinity.

Although many consequences of climate change on marine and terrestrial ecosystems are well documented, the characterisation of estuarine ecosystems specific responses and the drivers of the changes are less understood. In this study, we considered the biggest Southwestern European estuary, the Gironde, as a model of a macrotidal estuary to assess the effects of both large- (i.e., North Atlantic basin-scale) and regional-scale climate changes. Using a unique set of data on climatic, physical, chemical and biological parameters for the period 1978–2009, we examined relations between changes in both the physical and chemical environments and pelagic communities (plankton and fish) via an end-to-end approach. Our results show that the estuary experienced two abrupt shifts (∼1987 and ∼2000) over the last three decades, which altered the whole system. The timing of these abrupt shifts are in accordance with abrupt shifts reported in both marine (e.g., in the North Sea, the Mediterranean Sea and along the Atlantic) and terrestrial (e.g., in European lakes) realms. Although this work does not allow a full understanding of the dynamical processes through which climate effects propagate along the different compartments of the ecosystem, it provides evidence that the dynamics of the largest estuary of Southwest Europe is strongly modulated by climate change at both regional and global scales.

The Gironde is the largest estuary of South-West Europe and is one of the best monitored estuarine systems in the world. This macrotidal estuary is characterized by a low biodiversity in both oligo- and mesohaline zones. Its zooplankton community is constituted by only five major species, three calanoid copepods (including one invasive species) and two mysids. Retrospective analyses have already documented a warming associated to a phenomenon of marinisation. Here, we investigate the influence of both marinisation and warming on the spatial distribution and the abundance of copepods (i.e. Eurytemora affinis, Acartia bifilosa and neritic species) in the Gironde estuary. We modelled the environmental envelope of the copepods as a function of salinity and temperature to demonstrate that the alteration of their longitudinal distribution in the estuary between 1975 and 2003 was the result of both changing temperature and salinity. Although the upstream movement of neritic species was mostly related to salinity, we show that the augmentation of both temperature and salinity was at the origin of the upstream progression of both A. bifilosa and E. affinis. These results suggest that the distribution of copepods can be affected by both anthropogenic forcing and climatic change, which modulate the physic-chemistry of the Gironde estuary.