Les estuaires macrotidaux tels que l'estuaire de la Charente sont le siège d'une interaction constante entre la marée et le débit fluvial. L'objectif de ce travail est d'étudier le comportement de l'estuaire en fonction de ces forçages, et de déterminer leur impact sur les distributions horizontale et verticale de la salinité et des sédiments fins cohésifs. Un modèle tridimensionnel hydrosédimentaire a été mis en place sur l'estuaire afin de reproduire la dynamique estuarienne observée dans la Charente. Ce modèle a été validé via l'obtention de mesures in-situ venant également appuyer et compléter les simulations de réponse aux forçages effectuées. Dans l’estuaire de la Charente, l'asymétrie de la marée présente la particularité de s’inverser en fonction du cycle morte-eau/vive-eau. Le modèle a permis de déterminer l'influence de la marée incidente et de la morphologie de l'estuaire sur ce comportement, et d'évaluer son impact sur la salinité et la dynamique sédimentaire de l'estuaire. L'évolution globale de la marée lors de sa propagation dans l'estuaire a été étudiée, ainsi que l'influence du débit fluvial sur la circulation estuarienne, l'intrusion saline, et la stratification. Les résultats montrent que l'embouchure de l'estuaire reste dominée par la marée même en cas de crue, et que la stratification est inversement proportionnelle au débit fluvial. Le bouchon vaseux est reproduit par le modèle hydrosédimentaire, et ses variations en fonction des cycles de marée flot/jusant et morte-eau/vive-eau sont étudiées. La marée est le processus dominant dans la formation et le déplacement du bouchon vaseux. Les simulations montrent cependant une forte influence du débit fluvial sur sa géométrie et sa concentration, particulièrement en crue où il est plus compact et se déplace sur une distance plus courte. Les flux sédimentaires et les observations faites sur le terrain suggèrent que les sédiments sont importés dans l'estuaire en régime fluvial moyen et d'étiage, et qu'un envasement se produit. En crue, le bouchon vaseux est maintenu à 10 km en aval de l'embouchure et un export de sédiments vers la baie de Marennes-Oléron est obtenu. / Macrotidal estuaries such as the Charente estuary are characterized by a constant interaction between the tides and the river runoff. The aim of this work is to study the estuary behavior in function of these forcings, and to determine their impact of the horizontal and vertical distributions of salinity and fine cohesive sediments. A three-dimensional model was developed to reproduce the estuarine dynamics observed in the Charente estuary. This model was validated using in-situ measurements, which can also confirm and provide additional information when compared to the different forcing simulations. In the Charente estuary, the tidal asymmetry is characterized by its inversions in function of the neap/spring tidal cycle. The model was used to determine the influence of the incident tide and the estuarine morphology on this behavior, and to evaluate its impact on salinity and sediment dynamics in the system. The overall evolution of the tide during its propagation in the estuary was studied, together with the river runoff influence on the estuarine circulation, the saline intrusion and stratification. Results show that the estuary mouth stays tide-dominated even in the event of a flood, and that stratification is inversely proportional to the river runoff. The turbidity maximum is well reproduced by the hydrosedimentary model, and its variations infunction of the flood/ebb and neap/spring tidal cycles are studied. Tidal forcing is the main mechanism leading to the formation and movement of the turbidity maximum. However, simulations show a strong influence of the river runoff on its geometry and concentration, especially when the runoff is high. The turbidity maximum is then more compact and moving on shorter distances. Calculated sedimentary fluxes and observations made on the field suggest that sediments are imported in the estuary for low and medium river runoffs, and that siltation is occurring. In the event of a flood, the turbidity maximum is maintained 10km upstream of the mouth and sediments are exported into the Marennes-Oléron bay.

Cette thèse de Doctorat examine le réseau trophique estuarien lié aux herbiers à zostères, Zostera noltii et quantifie le rôle trophique des consommateurs de la macrofaune benthique, dans deux zones intertidales de l’estuaire du Mondego, à différentes périodes de 1993 à 2008. Elle s’intéresse spécifiquement (i) à l’incorporation de l’azote issu des activités humaines, en considérant l’assimilation d’azote comme un indicateur de l’eutrophication et (ii) au rôle des zostères dans le réseau trophique benthique. Six modèles ont été développés afin d’analyser les effets, (i) d’un enrichissement en nutriments, (ii) des mesures de mitigation, et (iii) d’une inondation centennale, sur les propriétés du réseau trophique benthique estuarien. La présence de Z. noltii change peu la structure du réseau trophique planctonique, soutenu en partie par la matière organique particulaire et supporte principalement des poissons comme prédateurs. Les autres consommateurs montrent une grande variabilité de signature isotopique, ce qui suggère qu’ils peuvent changer de régime alimentaire en fonction des changements de l’environnement. En revanche, les δ13C et δ15N des producteurs et consommateurs de l’estuaire du Mondego montrent très peu de variation saisonnière, malgré une saisonnalité météorologique marquée, ainsi qu’une forte variation saisonnière des paramètres de la colonne d’eau (apports en sels nutritifs et concentration en chlorophylle a). Les modèles à l’état stable montrent enfin que la structure trophique de la communauté benthique de l’estuaire du Mondego est affectée différemment par chacun des évènements particuliers étudiés. / This dissertation examines the estuarine food web related to the eelgrass Zostera noltii and quantifies the ecological trophic role of benthic macrofauna consumers, in intertidal areas of the Mondego estuary, covering different time periods from 1993 to 2008. It specifically focuses (i) on the incorporation of the nitrogen derived from human activities, considering the N uptake as an eutrophication index, and (ii) on the role of the eelgrass in the benthic food web. In addition, six mass-balanced models were developed to assess the effects of (i) a period of nutrient enrichment, (ii) the implementation of mitigation measures, and (iii) a centenary flood, on the benthic estuarine food web properties.

L'estuaire de l'Escaut est un estuaire en voie de restauration. L'étude s'intéresse à l'écologie de la communauté zooplanctonique dans le tronçon d'eau douce de l'Escaut, ou, suite à l'amélioration de la qualité de l'eau le copépode calanoide Eurytemora affinis est devenu dominant depuis 2007 et les copépodes cyclopoïdes ont diminués en abondance. Nous avons cherché à trouver quels facteurs environnementaux expliquent ce changement de la composition de la communauté zooplanctonique. Les résultats d'analyses RDA et GLM entre les abondances des taxons zooplanctoniques et les facteurs environnementaux montrent un lien étroit entre l'augmentation de l'abondance d'E. affinis et l'augmentation des concentrations en oxygène ainsi que la diminution des concentrations en N-NH4. En fait, le tronçon amont de l'estuaire est devenu 'permissive' pour le développement d'E. affinis à partir ou la concentration en O2 a dépassé le seuil de 4 mg L-1 et la concentration en N- NH4 est restée en dessous de 2 mg L-1. La cause du déclin en abondance des cyclopoids reste à trouver. Dans l'Escaut, le phytoplancton est fortement dominé par les diatomées, mais la concentration en Si dissoute s'avère parfois limitant. La question se pose sur quelles composantes de la communauté phytoplanctonique le zooplancton dominant se nourrit. La sélectivité de broutage d'E. affinis a été quantifiée à l'aide d'expériences d'incubation et des quantification de contenu pigmentaire à l'aide d'HPLC. E. affinis sélectionne des diatomées au sein de la communauté phytoplanctonique et en moindre mesure des cryptomonades. L'impact de la population d'E. affinis sur le stock de phytoplancton - et sur les diatomées dominantes- est < 4.5 % jour-1, ce qui implique que dans le tronçon d'eau douce de l'Escaut le zooplancton n'est pas limité par la nourriture et ne présente pas de limitation pour le développement les niveaux trophiques supérieurs. Certains taxons phytoplanctoniques (chlorophycées, par exemple) sont apparemment stimulés en croissance par la présence d'E. affinis dans les bouteilles expérimentales et l'impact précis d'E. affinis sur le phytoplancton non-diatomées est moins clair. L'activité de broutage du microzooplancton a également été testée avec des expériences d'incubation. Son impact sur la communauté phytoplanctonique est variable en intensité et en sélectivité, nécessitant plus d'expérimentation. / The Scheldt is an estuary on way of recovery. The study concerns the ecology of the zooplankton community in the freshwater reach of the estuary. In parallel to water quality improvement, the copepod Eurytemora affinis has become dominant since 2007 and abundance of cyclopoid copepods has decreased. We tried to find out which environmental factors had caused these changes in the zooplankton community composition. The results of RDA and GLM analysis between the abundance of zooplankton taxa and the environmental factors showed a strong link between E. affinis abundance and the increasing O2 concentration, but also the decreasing NH4-N concentration. The upstream Scheldt became permissive for E. affinis development as soon as oxygen concentration was above the threshold level of 4 mg L-1 and the NH4-N concentration remained below 2 mg L-1. The cause of the decrease in cyclopoid abundance remains unclear. The phytoplankton community of freshwater Scheldt is strongly dominated by diatoms, but the dissolved silica concentration could become limiting for their development. The question arises on which phytoplankton taxa the dominant zooplankton feeds. Grazing selectivity of E. affinis adults and CV was measured by incubation experiments using natural Scheldt water and by gut pigment content quantification. Phytoplankton taxa concentration was quantified by HPLC. E. affinis selects diatoms and sometimes cryptophytes. The impact of the E. affinis population on the phytoplankton standing stock is < 4.5% d-1, which means that the zooplankton community is not food limited and hence does not present a limitation to the development of higher trophic levels. The grazing activity of the microzooplankton community has also been measured by incubation experiments. Its impact on the freshwater Scheldt phytoplankton community is variable in intensity and in selectivity, and clearly needs further investigation.

Monomethylmercury, MeHg, is formed under anoxic conditions in waters, sediments and soils and then bioaccumulated and biomagnified in aquatic food webs, negatively effecting both human and wildlife health. It is generally accepted that precipitation of mercury, Hg, and adsorption of Hg to e.g. organic matter and mineral surfaces are important processes limiting the reactivity of Hg mobilized in the environment by natural and anthropogenic activities. However, knowledge concerning the role of different solid and adsorbed chemical forms of Hg for MeHg formation, evasion and bioaccumulation is missing. Such information is vital for the understanding of environmental processes controlling MeHg formation and bioaccumulation, as well as for predicting how changes in e.g. loading rates of atmospheric Hg and the outcome of climate change scenarios and anthropogenic land use could alter Hg concentrations in biota. In this thesis, a novel experimental approach, using isotopically enriched solid and adsorbed phases of inorganic Hg, HgII, as tracers, was developed. Using this approach, we successfully determined rates of MeHg formation from solid and adsorbed Hg species in sediment slurries and in mesocosm systems under conditions closely resembling those in field. We conclude that the solid/adsorbed phase speciation of HgII is a major controlling factor for MeHg net formation rates. Microcosm experiments revealed that newly formed MeHg was a major contributor to the evasion of MeHg from the water‒sediment system, emphasizing the importance of MeHg formation rate, rather than MeHg concentration, in the sediment for this process. From mesocosm systems, we provide experimental evidence, as well as quantitate data, for that terrestrial and atmospheric sources of HgII and MeHg are more available for methylation and bioaccumulation processes than HgII and MeHg stored and formed in sediments. This suggests that the contribution from terrestrial and atmospheric sources to the accumulation of Hg in fish may have been underestimated. As a consequence, in regions where climate change is expected to further increase land runoff, terrestrial MeHg sources may have even higher negative effects on biota than previously thought. Data and concepts presented in this thesis lay the basis for unprecedented in-depth modeling of processes in the Hg biogeochemical cycle that will improve our understanding and the predicting power on how aquatic ecosystems may respond to environmental changes or differences in loading rates for atmospheric Hg. / Monometylkvicksilver, MeHg, bildas under anoxiska förhållanden i naturliga vatten, sediment och jordar och bioackumuleras och magnifieras därefter i den akvatiska näringskedjan med negativa effekter på djur och människor som följd. Det är generellt vedertaget att utfällning av Hg och adsorption av Hg till exempelvis organiskt material och mineralytor begränsar tillgängligheten för biogeokemiska reaktioner av Hg som mobiliserats i miljön via naturliga och antropogena processer. Kunskap om betydelsen av speciationen av Hg i fasta och adsorberade faser för bildning, avgång och bioackumulering av MeHg är dock bristfällig. Denna information är kritisk för att förstå vilka processer som kontrollerar bildning och bioackumulering av MeHg samt för att kunna prediktera hur olika ekosystem kan förväntas svara på exempelvis ändrad deposition av atmosfäriskt Hg eller hur klimatförändringar kan påverka koncentrationerna av Hg i fisk. I denna avhandling har en experimentell metod utvecklades, där isotopanrikade fasta och adsorberade kemiska former av oorganiska tvåvärt Hg, Hg II används som s.k. "tracers". Denna metod användes för att bestämma MeHg bildningshasigheter i homogeniserade sediment prover samt i mesokosmsystem där förhållandena efterliknar de som förväntas i naturliga ekosystem. Från dessa drar vi slutsatsen att speciationen av HgII i fast/adsorberad fas är en viktig kontrollerande faktor som begränsar nettobildningen av MeHg. Mikrokosmexperiment visade att i första hand nyligt bildad MeHg avgick till gasfas vilket understryker betydelsen av MeHg bildningshastighet, snarare än koncentration, i sedimentet för denna process. Från mesokosmexperimenten visar vi, med kvantitativa data, att terrestra och atmosfäriska källor av HgII och MeHg är mer tillgängliga för bildning och bioackumulering av MeHg än HgII och MeHg lagrat eller bildat i sedimenten. Orsaken till detta är framförallt skillnad i speciationen av Hg i fasta/adsorberade faser. Detta innebär att bidraget från MeHg från terrestra och atmosfäriska källor till koncentrationen av Hg i fisk kan ha underskattats, samt att de negativa effekterna på MeHg exponering i områden där exempelvis klimat-förändringar förväntas leda till ökad terrest avrinning kan bli mer allvarliga än vad som tidigare predikterats. Data som presenteras i denna avhandling möjliggör modellering av Hg’s biogeokemiska cykel på en ny detaljnivå samt möjliggör säkrare prediktioner av hur olika ekosystem kan förväntas svara mot miljöförändringar eller ändrad deposition av atmosfäriskt Hg. / <p>Till Finansiärer skall också följande läggas till: Kempe stiftelsen (SMK-2942, SMK-2745, JCK-2413).</p>

La pêche repose sur des formes variées d’appropriation sociale des milieux aquatiques. Cette thèse s’attache à les définir dans le contexte particulier du bas Oyapock, estuaire d’un fleuve amazonien marquant la frontière entre la Guyane (France) et l’état d’Amapá (Brésil). Cet estuaire présente une importante diversité d’écosystèmes aquatiques (rivières, fleuves, forêts inondées, marais, mangrove et mer) et d’espèces végétales et animales qui les composent (près de 200 espèces y sont pêchées). La population du bas Oyapock forme un creuset culturel réunissant principalement Amérindiens, Créoles et Brésiliens, implantés dans deux villes et 40 villages. Par ailleurs, la présence d’un parc national sur le littoral brésilien et de trois territoires amérindiens implique des réglementations de l’accès aux ressources diverses. Dans ce contexte riche en diversité écologique et culturelle où émergent des conflits d’usage sur les territoires de pêche, cette thèse propose une lecture des dynamiques d’appropriation des ressources aquatiques. Les résultats s’appuient sur des données ethnographiques collectées d’octobre 2012 à octobre 2014. Celles-ci comprennent plus de 70 entretiens, 32 observations de sorties de pêche, l’inventaire du matériel de pêche, l’identification de 195 espèces pêchées et l’étude des taxonomies locales. L’étude des savoirs des pêcheurs révèle une connaissance fine des milieux aquatiques et de leurs rythmes, de l’écologie et de l’éthologie des animaux. Les pêcheurs fabriquent une grande variété d’engins de pêche adaptés tant aux espèces qu’aux espaces. Sur la base des savoirs partagés par les pêcheurs, différents groupes se distinguent et se spécialisent en fonction de grands milieux écologiques (savanes; fleuve et forêt ; embouchure et mer). La création de parcs nationaux, le contrôle croissant des flux transfrontaliers, l’urbanisation et la migration sont autant de changements contemporains auxquels les pêcheurs doivent faire face. Dans ce contexte, trois groupes d’habitants se démarquent : les pêcheurs professionnels de Saint-Georges (Guyane), ceux d’Oiapoque (Brésil) et les villageois Amérindiens de l’Uaçá (Brésil). Ils s’inscrivent dans une démarche de reconnaissance formelle de leur territoires de pêche afin d’en garantir l’accès à long terme. Engagés dans différentes stratégies, la réussite de leur démarche dépend de la prise en compte de leurs spécificités par les États. / Fishing is based on various forms of social appropriation of aquatic environment. This thesis seeks to define them in the specific context of the Lower Oyapock, estuary of an Amazonian river delineating the border between French Guyana and Amapá state (Brazil). This estuary presents a high variety of aquatic ecosystems (streams, rivers, flooded forests, swamps, mangroves and sea) and is home of high diversity of plant and animal species (over 200 species are caught). The population of the Lower Oyapock forms a cultural melting-pot principally composed by Amerindians, Creoles and Brazilians, established in two towns and 40 villages. Moreover, the presence of a national park along the Brazilian coast and three indigenous lands imply a regulation of access to natural resources. In this context rich in ecological and cultural diversity, where emerge conflicts over fishing territories, this thesis proposes a reading of the dynamics of appropriation of aquatic resources. Results are based on ethnographic data collected from October 2012 to October 2014. They range from more than 70 interviews, 32 fishing trips observations, the inventory of fishing gear, the identification of 195 fishes species, and a study of local taxonomies. The study of fishers’ knowledge reveals a detailed expertise about the aquatic environments, notably their rhythms, and the animal ecology and behavior. Fishermen make an important variety of fishing equipment adapted to both species and spaces. Based on the way knowledge is shared, different fishermen’s groups are characterized and specialized according to the ecological conditions/features (savanna; river and forests; river mouth and sea). Creation of national parks, increasing controls of cross-border flows, urbanization and migration are all contemporary challenges the fishermen are confronting. In this context, three residents groups stand out: professional fishermen from Saint-Georges (French Guyana), those from Oiapoque (Brazil), and the Indigenous villagers from Uaçá (Brazil). These three groups aim to obtain an official recognition of their fishing territories in order to ensure long-term access. Engaged in various strategies, their success in the process hinges on the States’ consideration of their specificities.

Interactions between fish utilizing nearshore habitats of the Fraser River estuary were investigated by field observations and laboratory experiments. Chum salmon fry (Oncorhynchus keta) were the most abundant salmonid captured between April and June. Non-salmonid species captured included: threespine stickleback (Gasterosteus aculeatus), prickly sculpin (Coitus asper), and peamouth chub (Mylocheilus caurinus). Potential predators included: prickly sculpin, and northern squawfish (Ptychocheilus oregonensis), but few had been feeding on fish. Chum fry fed predominantly on surface insects but the proportion of benthic prey in the diet increased over time. Stickleback shared the greatest diet overlap with chum fry. Interactions between two dissimilar prey, chum fry and threespine stickleback, and a predator, cutthroat trout (Oncorhynchus clarki) were investigated in the laboratory. Prey response to hungry and satiated predators was related to the degree of risk. Although attack rates by trout on chum and stickleback were similar, trout captured more stickleback than chum, but consumed both prey at similar rates. I tested the hypotheses that prey foraging efficiency is reduced in the presence of a predator and increased in the presence of alternate prey. When alone, chum fed on surface Drosophila and mid-water Daphnia, while stickleback fed on benthic Tubifex and Daphnia. The feeding efficiency of chum increased in the presence of stickleback and decreased in the presence of trout. Hatchery and wild chum showed opposite dietary shifts in the presence of trout. Hatchery chum shifted from surface to mid-water feeding and the number of fish feeding significantly decreased. Wild chum fed at the surface, at significantly decreased feeding rates. In the presence of stickleback and trout the feeding behaviour of chum was similar to that when chum were alone. Stickleback feeding behaviour was not affected by presence of trout or chum. Chum and stickleback detected Daphnia faster than Drosophila or Tubifex, and chum responded to Daphnia significantly faster than stickleback. Foraging time per item was significantly less for chum than stickleback. Habitat use by fish prey was investigated in the presence and absence of trout and alternate prey. Wild chum shifted from mid-water to the surface in the presence of trout, but returned to mid-water when stickleback were present. Stickleback fed in bottom habitats regardless of the presence of trout or chum. When prey were confined to specific depths in the water column, trout attacked chum more frequently than stickleback in all locations and attacked both prey more frequently within 24 cm of the substrate. Movement by prey did not affect the attack rate. When given a choice between a food-rich open water habitat and a food-deficient vegetated habitat in the presence of trout and alternate prey, chum and stickleback used vegetated refugia significantly more in the presence of trout. Alternate prey presence decreased the proportion of chum but increased the proportion of stickleback using vegetation. Behavioural responses to avoid predation significantly reduced the foraging efficiency of prey. Chum showed stronger responses to trout than stickleback. The presence of stickleback reduced the effect of predation on foraging efficiency. Possible explanations for the positive effect of stickleback on chum feeding efficiency were experimentally examined including: social facilitation, reduced intraspecific competition, and the calming influence of stickleback on chum behaviour ("dither"). The results suggest that stickleback have a calming influence on chum behaviour and that mixed species feeding groups may reduce intraspecific competition. / Science, Faculty of / Zoology, Department of / Graduate

L’objectif de notre étude sur les changements qui ont marqué l’évolution de la pêche artisanale au Gabon à partir du cadre de la province de l’Estuaire avait pour vocation d’une part, sur l’appui d’archives révélant l’organisation du secteur pêche durant la période coloniale et d’autre part sur la base d’enquêtes menées dans plusieurs villages, d’appréhender les changements encourus dans cette activité, qui est en cours de passage d’un cadre traditionnel et artisanal à un autre cadre plus hétéroclite.Ce nouveau cadre hétéroclite de la pêche artisanale se révèle aujourd’hui tout d’abord à travers la présence des communautés de pêcheurs issues d’origines ethniques diverses, dans lesquelles nous avons pu observer des interactions riches de partage de savoirs et de savoir-faire ; ensuite, à travers des interactions entre ces communautés de pêcheurs et l’environnement des territoires dans lesquels elles sont ancrées. Nous avons ainsi mis à jour une croissance démographique des acteurs de ce secteur d’activité.Au de-là donc de l’analyse de la dynamique des changements, nous voulions démontrer une évolution des rapports entre les pêcheurs et leur environnement sociopolitique, économique d’une part, et de répondre d’autre part à la problématique de l’articulation entre la dynamique des changements sociaux dans ces sociétés pluriethniques et la dynamique de l’espace littoral qu’elles se partagent. / The aim of our study on the changes that have marked the development of artisanal fisheries in Gabon from the part of the province of the estuary was intended on the one hand, the support of record showing the organization of the fisheries sector during the colonial period and partly on the basis of surveys conducted in several villages, to understand the changes involved in this activity, which is currently moving from a traditional craft and another part more heterogeneous.This new framework assorted artisanal fisheries now appears first through the presence of fishing communities from various ethnic backgrounds, in which we observed rich interactions of sharing knowledge and know-how; Then, through interactions between fishing communities and the environment of the territories in which they are embedded. We have updated a population growth of players in this industry.Beyond the analysis of the dynamics of changes, we wanted to show a changing relationship between fishermen and their socio-political environment, economic on the one hand, and answer the other hand the problem of the joint between the dynamics of social change in these companies enjoyed riethniques and dynamics of the coastal area they share.

Les estuaires, situés à l’interface entre les domaines continental et marin, constituent des zones essentielles dans les échanges de matières. Ils jouent dès lors un rôle capital pour les cycles biogéochimiques et biologiques et subissent, par ailleurs, des pressions climatiques et anthropiques croissantes depuis plusieurs décennies. Le présent travail a été focalisé sur les peuplements benthiques et pélagiques présents dans la partie fluviale (Garonne et Dordogne) de l’estuaire de la Gironde, zone àtrès faible salinité où ces peuplements n’avaient encore jamais été étudiés. Alors que la méiofaune, composée principalement de Nématodes, s’est avérée relativement abondante dans les domaines intertidal et subtidal, le macrobenthos est apparu composé essentiellement d’Oligochètes en intertidal et complètement absent en subtidal. La grande plasticité du copépode dominant Eurytemora affinis a été confirmée, celui-ci occupant une niche écologique différente dans la partie fluviale de l’estuaire par rapport à la zone haline. L’importance de la température plutôt que la qualité du pool nutritif sur la productivité d’E. affinis a été démontrée, mettant en évidence une fois de plus la grande adaptabilité de cette espèce dans un habitat très fluctuant. L’étude de l’habitat benthique et pélagique, notamment en terme de qualité du pool nutritif disponible pour les organismes, a démontré que la contribution de la matière organique réfractaire d’origine terrestre est dominante. La contribution du micro phytobenthos à la composition de la matière organique sédimentaire et pélagique a aussi été mise en évidence. Enfin,l’étude des communautés planctoniques dans la partie fluviale de l’estuaire de la Gironde a montré que l’espèce E. affinis y occupe une position clef. / Being at the interface between continental and marine systems, estuaries are essential areas for matter exchanges. Therefore, they play a crucial role in biological and biogeochemical cycles. In addition to natural fluctuations, these systems have also undergone increasing climate and anthropogenic pressures for several decades. The present work focused on the benthic and pelagic assemblages in the fluvial section (Garonne and Dordogne rivers) of the Gironde estuary, a low salinity area where these communities had never been studied. Meiofauna, mainly composed ofnematodes, was found in relatively high abundance in both intertidal and subtidal zones.Macrozoobenthos was essentially composed of oligochaetes in the intertidal, while it was totally absent in the subtidal areas. The high plasticity of the dominant copepod Eurytemora affinis was confirmed, with a different ecological niche in the freshwater section of the estuary compared to the haline area downstream. The importance of temperature rather than the quality of the nutrient pool on the productivity of E. affinis was demonstrated, thereby confirming the great adaptability of thisspecies to a highly fluctuating habitat. Study of benthic and pelagic habitat, especially in terms of quality of the nutrient pool available to the organisms, showed that the contribution of refractoryorganic matter with a terrestrial origin is dominant. A significant contribution of microphytobenthos to the composition of sedimentary and pelagic organic matter was also highlighted. Finally, the study of planktonic communities in the fluvial part of the Gironde estuary showed that the species E. affinis occupies a key position in this part of the estuary.

Estuaries are widely recognized as important habitats for the early life history stages of commercially and recreationally important marine fish species. In general the estuaries of northeast Florida are understudied, and there is a need to characterize the ichthyoplankton community at this important faunal boundary between temperate and tropical marine zones. To determine community structure and temporal patterns in the distribution and abundance of larval fish ingressing in to the Guana-Tolomato-Matanzas (GTM) estuary through its two inlets (St. Augustine and Matanzas), ichthyoplankton were sampled bi-weekly for one year at both inlets during nighttime spring flood tides beginning in March 2012. Samples were collected with a plankton net (1 m diameter with 1mm mesh) suspended 1 m below the surface in the water column. Over 30,000 individuals were collected, representing 74 taxa. Four families made up 90 % of the collection: Gobiidae (34.8 %), Sciaenidae (26.1 %), Engraulidae (19.3 %), and Gerreidae (9.3 %). Examination of the ichthyoplankton community revealed seasonal trends in species richness and in larval fish density; species richness and larval fish density were generally greatest during the protracted summer season. Spring and summer pulses in recruitment were evident in nearshore summer spawners (e.g., gobiids and engraulids), and winter peaks in recruitment were evident in marine spawned species (e.g., sciaenids, sparids, haemulids). The variety of taxa collected, and the patterns in the seasonal species assemblage of the ichthyoplankton community of the GTM estuary align with its geographical position near a faunal boundary.

Os sistemas estuarinos são ambientes de transição entre o continente e o oceano, onde atividades humanas são intensivamente desenvolvidas. O Sistema Estuarino de Santos e São Vicente, localizado na porção central do Litoral do Estado de São Paulo, tem se destacado como um dos principais pólos econômicos do Brasil, devido ao complexo petroquímico e siderúrgico, ao Porto de Santos e à aptidão turística da região. O rápido e intenso desenvolvimento, a partir da década de 40, resultou na degradação do ecossistema local devido à introdução de esgotos e efluentes não-tratados, bem como ao aporte atmosférico de substâncias nocivas. O objetivo principal deste trabalho foi determinar as concentrações de hidrocarbonetos marcadores geoquímicos em sedimentos de testemunhos, para traçar o histórico da contribuição destes compostos ao longo dos últimos 100 anos, relacionando os resultados com a ocupação urbano-industrial da região. Paralelamente, procurou-se determinar a origem da matéria orgânica sedimentar (C, N e S) assim como verificar a existência de correlação estatística entre os hidrocarbonetos e a susceptibilidade magnética, ou seja, indicadores de poluição de natureza distinta. Quatro testemunhos foram coletados em áreas de mangue e próximas à fontes pontuais de poluição, como o lixão do Alemoa, o terminal petrolífero do Alemoa e próximo ao acesso do Pólo Industrial de Cubatão. A identificação e quantificação dos hidrocarbonetos foram feitas por um cromatográfo a gás acoplado a um detector de ionização de chama (GC-FID) para os hidrocarbonetos alifáticos e a um espectrômetro de massa (GC-MS) para os hidrocarbonetos policíclicos aromáticos (PAHs). A análise granulométrica mostrou o predomínio de sedimentos lamosos nos sedimentos mais recentes, devido a progradação das áreas de mangue e às atividades antrópicas como o escorregamento de morros adjacentes e a dragagem de canais. A aumento no teor do nitrogênio (Ntot.) nas secções próximas ao topo dos testemunhos é proveniente das indústrias de fertilizantes e do lançamento de esgotos não-tratados. Embora tenha ocorrido um aumento na concentração de n-alcanos de fontes antrópicas ao longo dos últimos anos, a introdução biogênica aparece como um importante componente no total dos n-alcanos, sendo atribuída à contribuição dos múltiplos rios que deságuam no estuário e do mangue adjacente. A distribuição da concentração dos hidrocarbonetos alifáticos, em particular a mistura complexa não resolvida, foi relacionada com o desenvolvimento do Pólo Industrial de Cubatão e do Porto de Santos, à deposição de resíduos sólidos no morro do Alemoa e à adoção de medidas de controle de poluição por parte das indústrias da região. Em relação aos PAHs, foi possível estabelecer as principais fontes (petrogênica ou pirolítica) destes compostos ao longo dos testemunhos. O predomínio de PAHs de maior peso molecular (4 – 6 anéis), indicou contribuição antrópica da queima de biomassa, carvão, óleo bruto e combustíveis fósseis. A correlação estatística entre hidrocarbonetos e susceptibilidade magnética mostrou a aplicabilidade deste parâmetro na avaliação preliminar do histórico da poluição de sedimentos marinhos. O aporte de metais magnéticos, caracterizado pela susceptibilidade magnética, foi associado a diferentes fontes antrópicas de hidrocarbonetos e aos principais eventos históricos relacionados com o desenvolvimento urbano-industrial da Baixada Santista. / Estuarine areas are environments between land and ocean, where human activities are intensively developed. The Santos and São Vicente Estuary, located on the central portion of the coast of São Paulo state, has one of the most important industrial areas of Brazil. The increasing of urbanization and industrialization near the margins of Estuary, in the 50’s, has been responsible for the degradation of the mangrove, for the discharge of sewage, and consequently, it affects the input of organic matter and sedimentary deposition. The main objective of this work was to determine the concentration of hydrocarbons biomarkers in sediment cores in order to investigate the input of these substances in the last 100 years, and to find a relation with the urban and industrial occupation in this area. The organic matter origins (C, N and S) are also studied. A possible statistical correlation between two different pollution indicators (hydrocarbons and magnetic susceptibility) was investigated. Four sediments cores are collected in mangrove areas and near polluted places, as Alemoa garbage disposal, Alemoa petroliferous terminal and Cubatão industrial complex. Hydrocarbons concentrations were determined by gas chromatograph with flame ionization detector (GC-FID) for aliphatic compounds and by gas chromatograph coupled with mass spectrometer for polycyclic aromatic hydrocarbons (PAHs). The grain-size analyses showed that in the recent sediments, mud was predominant. It was associated with the mangrove progradation and anthropogenic activities such as settlement, garbage disposal and sweep activities. High nitrogen concentrations were found in the sediments near the top of the cores and it was associated with inputs from untreated sewage and industries. Although a large anthropogenic input of n-alkanes was detected in the recent sediments, the biogenic contribution by rivers and direct input from mangrove vegetation is an important in the total n-alkanes. The distribution of aliphatic hydrocarbons in the cores, meanly concerning “Unresolved Complex Mixture”, was associated with the formation and development of Cubatão industrial complex and the Santos harbour, waste disposal in Alemoa hill and with the preservation program, that results in the improvement of waste treatment and decrease of organic pollutants input in this area. The PAHs analyses indicated multiplies sources of these compounds (petrogenic and pyrolitic). The predominance of higher molecular weight compounds (4 – 6 aromatic rings) showed anthropogenic contribution from biomass, coal, oil and fossil fuels combustion. Statistical correlation of magnetic susceptibility with hydrocarbons indicated that the input of magnetic metals could be associated with several sources of hydrocarbons, related with the urban and industrial development of Santos and São Vicente Estuary.