Le gouvernement français a fixé pour objectif que 23% de la consommation énergétique proviendraitdes énergies renouvelables, y compris les énergies renouvelables marines pour 2020. Huit parcs éoliensen mer sont prévus le long des côtes françaises Atlantique-Manche, parmi lesquels le site de Dieppe-LeTréport dans la partie orientale de la Manche. Afin de mieux connaître la structure et le fonctionnementde cet écosystème avant l'installation du parc éolien, ma thèse est axée sur la construction de modèlesde réseau trophique à l’aide du logiciel Ecopath sur ce site d’implantation en comparaison avec deshabitats benthiques similaires en Manche. La collecte de nouvelles données sur les compartimentsbiologiques (zooplancton, suprabenthos, méiofaune, benthos et poissons démersaux) est essentielle.Ainsi, quatre campagnes (étés 2014/2015, hivers 2015/2016) ont permis d'estimer la contribution dechaque groupe zoologique dans deux habitats benthiques principaux : les graviers ensablés/sablesgraveleux et les sables moyens sur le site (environ 30 km²) correspondant à deux communautésbenthiques largement répandues en Manche. La macrofaune a été échantillonnée avec une benne VanVeen, le suprabenthos avec un traîneau Macer-Giroq modifié avec une station dans chaque habitatbenthique (échantillonnage jour et nuit) et les poissons avec un chalut à perche. Au total, 1 584 poissonsdémersaux ont été recueillis et leurs contenus stomacaux ont été examinés. Les résultats montrent quele site se distingue par la forte contribution des bivalves en termes de biomasses et que les crustacés sontdes proies préférentielles des poissons. Ce lien est discuté à travers l’analyse du réseau trophique avecun focus sur les espèces consommées et non consommées de communautés benthiques, et la notion decul de sac trophique. / The French government has set a target of 23% of energetic consumption derived from renewable energysources including Marine Renewable Energy for 2020. Eight offshore wind farms (OWF) are plannedalong the Atlantic-English Channel French coasts and among them Dieppe-Le Tréport site in the easternpart of the English Channel. In order to gain further knowledge on the ecosystem structure andfunctioning before the OWF installation, my PhD thesis is focused on the construction of an EcopathModel on the wind farm site in comparison with similar benthic habitats from the English Channel. Thecollection of new data on biological compartments (zooplankton, suprabenthos, meiofauna, benthos anddemersal fishes) are essential. Four cruises (summers 2014 /2015 and winters 2015 /2016) allowed toestimate the contribution of each zoological group in two main benthic habitats: i.e. sandy gravels andmedium clean sands, founded on the site (about 30 km²), corresponding to two microbenthiccommunities well represented in the English Channel. Macrofauna was sampled with a Van Veen grab,suprabenthos with a modified Macer-Giroq sledge in one station from each benthic habitat (day andnight sampling) and fish with a beam trawl in ten stations. A total of 1,584 demersal fishes has beencollected and their stomach contents has been examined. The results show the importance of largebivalves in the benthic biomass whereas the crustaceans are preferential preys of fishes. This link isdiscussed within the trophic network between consumed and non-consumed species of benthiccommunities, and the concept trophic ‘cul de sac’.

<p>Att bevarandet av biologisk mångfald är en grundpelare för att nå en hållbar utveckling enades världens länder om i Konventionen om biologisk mångfald (CBD) som upprättades under toppmötet i Rio de Janeiro 1992. I konventionen förespråkas den s.k. ekosystemansatsen (EA), vilket är en strategi som innebär en helhetssyn på ekosystem. Syftet med denna uppsats är att undersöka i vilken grad EA tillämpas på nationell och regional nivå. Frågan är också om EA är en bra utgångspunkt för att upprätthålla biologisk mångfald på landskapsnivå samt vad som kan öka tillämpningen av EA på regional nivå. På nationell nivå analyserades två delar i miljömålspropositionen och på regional nivå analyserades de landskapsstrategier som sju län har fått i uppdrag av regeringen att upprätta i ett pilotprojekt. Min teoretiska utgångspunkt har varit ekosystemansatsen och dess principer och vägledande punkter. Metoden bestod av främst en kvantitativ innehållsanalys med kvalitativa inslag och som komplement utfördes fyra intervjuer.</p><p>Resultatet visade att de delar av miljömålspropositionen som analyserades i hög grad följde ekosystemansatsen. En brist i propositionen var dock att det saknades riktlinjer om att det behövdes involvering av olika aktörer när den ursprungliga definitionen av landskapsavsnittet i strategierna skulle bestämmas. Att denna aspekt var implicit ledde troligtvis till det faktum att den även var implicit i landskapsstrategierna. Tillämpningen av EA i landskapsstrategierna skedde, trots att länsstyrelserna endast tillämpade den indirekt, i ganska hög grad och särskilt togs hänsyn till sociala aspekter som involvering av olika aktörer i själva processen och kontakt med vetenskapliga discipliner. Det som däremot var bristfälligt gällde tillämpningen av komplexa aspekter, vilka inte klart hade uttryckts i riktlinjerna till länsstyrelserna från regeringen. Dessa faktorer var beaktande av förvaltning av ekosystem inom ramen för dess funktion, processer i ekosystem samt adaptiv förvaltning. Alla intervjupersoner var överens om att EA är övergripande och ganska luddig, men det måste den vara för att gälla globalt. Av vikt är att konkretisera den på nationell och regional nivå. Ett förslag är att Naturvårdsverket i detta projekt ger tydliga riktlinjer angående tillämpningen av EA i landskapsstrategierna och att det är en tvåvägskommunikation mellan Naturvårdsverket och länsstyrelserna så att det blir en iterativ process. Genom en konkretisering kan tillämpningen av EA öka och därmed ett steg tas mot en hållbar utveckling.</p> / <p>The Convention on Biological Diversity (CBD) promotes the Ecosystem Approach (EA), which is a strategy that endeavours to take a comprehensive approach to managing ecosystems. The aim of this report is to study to what degree the EA is being followed on a national and regional level. A key question of the research is whether EA is conceptually sound and whether it has been operationalised effectively at both national and regional scale. Using articulated EA principles and operational guidelines from the CBD this study analyzed the Government's national environmental directive concerning biodiversity. The same approach was also applied to an analysis of several regional landscape strategies that are being developed as part of a pilot project. The results show that the national biodiversity directive is largely consistent with an EA. Although one area of inadequacy was the level of involvement by different stakeholders in the original decision about defining the landscape area in the pilot studies. This was also a weakness in the landscape strategies- perhaps because communication on this issue was not explicit in the directive from the government.</p><p>The implementation of EA in the landscape strategies at the regional level was also found to be good, especially the participation from different stakeholders (especially local stakeholders) in the process and scientific institutions. However inadequate factors not represented in these strategies were complex ecological aspects such as principle 6 (ecosystem must be managed within the limits of their functioning) and operational guideline 1 (focus on the functional relationships and processes within ecosystems). Adaptive management (operational guideline 3), a relatively new approach in Sweden, was also found to be deficient. All the respondents agreed that the EA needed to be made more concrete on a national and regional level. A suggestion from the research to improve the development and adoption of the EA would be to develop iterative mechanisms between regional and national authorities to ensure national guiding principles are informed by more concrete regional experience. When the EA is implemented more effectively we will take one step further on the way to reaching a sustainable development.</p>

This dissertation evaluates the role and effectiveness of law in the transboundary environmental governance of the Baltic Sea with regard to eutrophication. To this end, it reviews the applicable international agreements with their related instruments, as well as the EU legal frameworks, for the protection of the Baltic Sea environment on the basis of theories on resilience in social-ecological systems. The scientific discourse on resilience in social-ecological systems provides theories on effective governance of complex environmental problems with nonlinear causal connections. The governance features identified in resilience governance also show significant similarities with characteristic features of the concept of ecosystem approach. The resilience features can thus provide guidance to the operationalization of this concept, which lacks a distinct meaning in the legal context. Eutrophication is one of the main environmental problems in the Baltic Sea. Despite the fact that this problem has been acknowledged since the 1970s, only little progress has been visible in the attempts to limit the problem. Environmental governance in the form of cooperation and common action has, however, been established by the coastal states of the Baltic Sea to reduce the discharges to their common resource. This was originally coordinated through the Helsinki Convention and its administrative organization HELCOM in the 1970s. Since the year 2000 a new set of legal instruments and approaches have developed, emphasizing also the ecosystem approach. These instruments have a basis both in HELCOM and in EU environmental law, most significantly represented by the Water Framework Directive and the Marine Strategy Framework Directive. They establish a unique regulatory structure, with new approaches to regulation, which also give rise to questions regarding interpretation and effectiveness that have not previously been analyzed. It is concluded that applicable law in the Baltic Sea area reflects resilience features such as adaptability, flexibility and redundancy within the legal structure. The legal structure for the Baltic Sea is dynamic and stretches over many levels of governance. The applicable legal instruments are constructed so as to be adaptable and flexible. The legal instruments moreover include significant elements that provide for participation at different levels and in different forms, which contribute to enabling the mentioned resilience features. However, the Baltic Sea legal structure – as law in general – has different core functions than just providing for effective environmental governance. Law is based in a number of general principles connected to the rule of law and the function of law as a foundation for stability in the society and in human interactions. These principles are also important since they are directly linked to enforcement, monitoring and control. While the legal structure in the Baltic Sea may provide for effective governance and social-ecological resilience, the resilience features reflected in law do not always appear as far-reaching as suggested by resilience theories, much due to the legal principles. It is however because of these principles and the base for binding requirements they enable, that law can push for governance measures and features that might not have been accomplished otherwise. This, in the larger perspective, includes creating requirements that steer human activities away from critical thresholds. / Baltic Ecosystem Adaptive Management, BEAM

Ce travail représente une contribution originale à la méthodologie pour le développement de modèles écosystémiques ainsi qu'une première tentative d'une modélisation end-to-end (E2E) de l'écosystème du Courant de Humboldt Nord (ECHN). L'objectif principal du modèle développé dans cette thèse est de construire un outil de gestion écosystémique et d'aide à la décision; raison pour laquelle la crédibilité du modèle est essentielle, laquelle peut-être établie par confrontation aux données. En outre, le ECHN présente une grande variabilité climatique et océanographique à différentes échelles, la source principale de variation inter-annuelle étant l'interruption du cycle d'upwelling saisonnier par l'Oscillation Australe du phénomène El Niño qui a un effet direct sur la survie larvaire et le succès de recrutement des poissons. La pêche peut aussi être fortement variable, en fonction de l'abondance et de l'accessibilité des principales ressources halieutiques. Ce contexte amène deux questions méthodologiques principales que nous explorons dans cette thèse à travers le développement d'un modèle E2E qui couple le modèle OSMOSE, pour la partie haut niveau trophique, au modèle ROMS-PISCES, pour les parties hydrodynamique et biogéochimie:(i) Comment calibrer un modèle écosystémique à partir de séries temporelles de données? (ii) Comment inclure l'impact de la variabilité inter-annuelle de l'environnement et de la pêche? En premier lieu, cette thèse met en évidence plusieurs problèmes liés à la confrontation de modèles écosystémiques complexes aux données et propose une méthodologie pour une calibration séquentielle en plusieurs phases des modèles écosystémiques. Nous proposons deux critères pour classer les paramètres d'un modèle: la dépendance au modèle et la variabilité temporelle des paramètres. A partir de ces critères, et en tenant compte de l'existence d'estimations initiales, on énonce des règles qui permettent de déterminer quels paramètres doivent être estimés, et dans quel ordre, dans le processus de calibration séquentiel. De plus, un nouvel Algorithme Évolutionnaire, conçu pour la calibration de modèles stochastiques et optimisé pour l'estimation du maximum de vraisemblance, a été développé et utilisé pour la calibration du modèle OSMOSE avec des séries temporelles de données.La variabilité environnementale est explicite dans le modèle: le modèle ROMS-PISCES force le modèle OSMOSE et propage les effets bottom-up potentiels dans le réseau trophique à travers les interactions trophiques entre plancton et poisson d'une part, et les changements dans la distribution spatiale du poisson d'autre part. Cette dynamique spatiale des poissons est prise en compte par l'utilisation de modèles de distribution des espèces de type présence/absence, qui sont en général évalués grâce à une matrice de confusion et les indicateurs statistiques qui lui sont associés. Toutefois, quand on considère la prédiction d'un habitat au cours du temps, la variabilité de la distribution spatiale des habitats peut être résumée de manière complémentaire et validée en utilisant les patrons émergents de la forme des distributions spatiales. Nous avons modélisé l'habitat potentiel des principales espèces du ECHN en utilisant plusieurs sources d'information (pêches commerciales, campagnes scientifiques et suivi satellite des navires de pêche) conjointement aux données environnementales issues d'observations satellites et in-situ, de 1992 à 2008. L'habitat potentiel est estimé sur cette période d'étude avec une résolution mensuelle, et le modèle est validé à partir d'informations du système, en utilisant une approche pattern-oriented.Le modèle écosystémique E2E ROMS-PISCES-OSMOSE pour le ECHN est calibré en une approche par maximum de vraisemblance pour ajuster des séries temporelles mensuelles de 1992 à 2008. En conclusion,quelques applications potentielles du modèle pour la gestion des pêches sont présentées et nous discutons leurs limitations et les perspectives. / This work represents an original contribution to the methodology for ecosystem models' development as well as the first attempt of an end-to-end (E2E) model for the Northern Humboldt Current Ecosystem (NHCE). The main purpose of the developed model is to build a tool for ecosystem-based management and decision making, reason why the credibility of the model is essential, and this can be assessed through confrontation to data. Additionally, the NHCE exhibits a high climatic and oceanographic variability at several scales, the major source of interannual variability being the interruption of the upwelling seasonality by the El Nino Southern Oscillation, which has direct effects on larval survival and fish recruitment success. Fishing activity can also be highly variable, depending on the abundance and accessibility of the main fishery resources. This context brings the two main methodological questions addressed in this thesis, through the development of an end-to-end model coupling the high trophic level model OSMOSE to the hydrodynamics and biogeochemical model ROMS-PISCES: i) how to calibrate ecosystem models using time series data and ii) how to incorporate the impact of the interannual variability of the environment and fishing.First, this thesis highlights some issues related to the confrontation of complex ecosystem models to data and proposes a methodology for a sequential multi-phases calibration of ecosystem models. We propose two criteria to classify the parameters of a model: the model dependency and the time variability of the parameters. Then, these criteria along with the availability of approximate initial estimates are used as decision rules to determine which parameters need to be estimated, and their precedence order in the sequential calibration process. Additionally, a new Evolutionary Algorithm designed for the calibration of stochastic models (e.g Individual Based Model) and optimized for maximum likelihood estimation has been developed and applied to the calibration of the OSMOSE model to data time series.The environmental variability is explicit in the model: the ROMS-PISCES model forces the OSMOSE model and drives potential bottom-up effects up the foodweb through plankton and fish trophic interactions, as well as through changes in the spatial distribution of fish. The latter effect was taken into account using presence/absence species distribution models which are traditionally assessed through a confusion matrix and the statistical metrics associated to it. However, when considering the prediction of the habitat against time, the variability in the spatial distribution of the habitat can be summarized and validated using the emerging patterns from the shape of the spatial distributions. We modeled the potential habitat of the main species of the Humboldt Current Ecosystem using several sources of information (fisheries, scientific surveys and satellite monitoring of vessels) jointly with environmental data from remote sensing and in situ observations, from 1992 to 2008. The potential habitat was predicted over the study period with monthly resolution, and the model was validated using quantitative and qualitative information of the system using a pattern oriented approach.The final ROMS-PISCES-OSMOSE E2E ecosystem model for the NHCE was calibrated using our evolutionary algorithm and a likelihood approach to fit monthly time series data of landings, abundance indices and catch at length distributions from 1992 to 2008. To conclude, some applications of the model for fishery management are presented and their limitations and perspectives discussed.

Att bevarandet av biologisk mångfald är en grundpelare för att nå en hållbar utveckling enades världens länder om i Konventionen om biologisk mångfald (CBD) som upprättades under toppmötet i Rio de Janeiro 1992. I konventionen förespråkas den s.k. ekosystemansatsen (EA), vilket är en strategi som innebär en helhetssyn på ekosystem. Syftet med denna uppsats är att undersöka i vilken grad EA tillämpas på nationell och regional nivå. Frågan är också om EA är en bra utgångspunkt för att upprätthålla biologisk mångfald på landskapsnivå samt vad som kan öka tillämpningen av EA på regional nivå. På nationell nivå analyserades två delar i miljömålspropositionen och på regional nivå analyserades de landskapsstrategier som sju län har fått i uppdrag av regeringen att upprätta i ett pilotprojekt. Min teoretiska utgångspunkt har varit ekosystemansatsen och dess principer och vägledande punkter. Metoden bestod av främst en kvantitativ innehållsanalys med kvalitativa inslag och som komplement utfördes fyra intervjuer. Resultatet visade att de delar av miljömålspropositionen som analyserades i hög grad följde ekosystemansatsen. En brist i propositionen var dock att det saknades riktlinjer om att det behövdes involvering av olika aktörer när den ursprungliga definitionen av landskapsavsnittet i strategierna skulle bestämmas. Att denna aspekt var implicit ledde troligtvis till det faktum att den även var implicit i landskapsstrategierna. Tillämpningen av EA i landskapsstrategierna skedde, trots att länsstyrelserna endast tillämpade den indirekt, i ganska hög grad och särskilt togs hänsyn till sociala aspekter som involvering av olika aktörer i själva processen och kontakt med vetenskapliga discipliner. Det som däremot var bristfälligt gällde tillämpningen av komplexa aspekter, vilka inte klart hade uttryckts i riktlinjerna till länsstyrelserna från regeringen. Dessa faktorer var beaktande av förvaltning av ekosystem inom ramen för dess funktion, processer i ekosystem samt adaptiv förvaltning. Alla intervjupersoner var överens om att EA är övergripande och ganska luddig, men det måste den vara för att gälla globalt. Av vikt är att konkretisera den på nationell och regional nivå. Ett förslag är att Naturvårdsverket i detta projekt ger tydliga riktlinjer angående tillämpningen av EA i landskapsstrategierna och att det är en tvåvägskommunikation mellan Naturvårdsverket och länsstyrelserna så att det blir en iterativ process. Genom en konkretisering kan tillämpningen av EA öka och därmed ett steg tas mot en hållbar utveckling. / The Convention on Biological Diversity (CBD) promotes the Ecosystem Approach (EA), which is a strategy that endeavours to take a comprehensive approach to managing ecosystems. The aim of this report is to study to what degree the EA is being followed on a national and regional level. A key question of the research is whether EA is conceptually sound and whether it has been operationalised effectively at both national and regional scale. Using articulated EA principles and operational guidelines from the CBD this study analyzed the Government's national environmental directive concerning biodiversity. The same approach was also applied to an analysis of several regional landscape strategies that are being developed as part of a pilot project. The results show that the national biodiversity directive is largely consistent with an EA. Although one area of inadequacy was the level of involvement by different stakeholders in the original decision about defining the landscape area in the pilot studies. This was also a weakness in the landscape strategies- perhaps because communication on this issue was not explicit in the directive from the government. The implementation of EA in the landscape strategies at the regional level was also found to be good, especially the participation from different stakeholders (especially local stakeholders) in the process and scientific institutions. However inadequate factors not represented in these strategies were complex ecological aspects such as principle 6 (ecosystem must be managed within the limits of their functioning) and operational guideline 1 (focus on the functional relationships and processes within ecosystems). Adaptive management (operational guideline 3), a relatively new approach in Sweden, was also found to be deficient. All the respondents agreed that the EA needed to be made more concrete on a national and regional level. A suggestion from the research to improve the development and adoption of the EA would be to develop iterative mechanisms between regional and national authorities to ensure national guiding principles are informed by more concrete regional experience. When the EA is implemented more effectively we will take one step further on the way to reaching a sustainable development.

Starting with the idea that unsustainable practices contribute to issues of social justice and poverty as much as to ecological issues. Chapter 1 traces the origins of the terms sustainable and development individually to see how it is that they came together. Chapter 2 traces the major international conferences and documents and their use of the terms sustainable development. Chapter 3 takes a phenomenology approach to get a bit deeper into sustainable development. I examine the most commonly cited definition of sustainable development as well as a broader definition of sustainable development as a process of change. Chapter 4 examines the field of environmental ethics and argues that constant debates over value distract policy makers from the central question of what morally motivates people to support environmental ethics views. Chapter 5 examines the institution and regime building process, and the conclusion offers three questions to measure our progress.

>Magister Scientiae - MSc / Understanding of Groundwater Dependent Ecosystems (GDEs) and their extent within the Table Mountain Group (TMG) aquifer is poor. To understand the dependence to basic ecological and hydrogeological concepts need explanation. The use of current literature aided in identification and classification. From the literature it has come clear that groundwater dependence centers around two issues, water source and water use determination. The use of Geographical Information System (GIS) showed its potential in proof of water sources. Rainfall data and a Digital Elevation Model (DEM) for the Uniondale area have been used to do watershed delineation, which is in line with locating GDEs on a landscape. Thus the conceptual approach should be a broad one that sets a basis for both investigation (scientific research) and institutional arrangements (management). On the scientific research aspect: 1) Methods used to ascertain groundwater dependence have been identified and described (for example morphological traits, physiological traits, etc.) a) Use of GIS to delineate watersheds in the Uniondale area, putting it as one of useful methods that can be used in locating GDEs in a landscape. b) Use of Digital Elevation Models (DEMs) to create both geological and topographic cross-sections. Topographic cross-sections are important to locate ecosystems along a landscape, while geological cross-sections are useful in conceptualising groundwater flow. 2) The Plant Functional Type concept, which puts together plant species regardless of phylogeny but rather on morphological, phenological and physiological/life history trait similarity, has been suggested as a useful concept for the TMG GDEs. On the management aspect: 1) An ecosystem approach to understand groundwater has been identified and modified to suite the TMG GDE management. 2) A retention strategy useful to manage the TMG GDEs effectively has been suggested. There are knowledge gaps that exist in the TMG aquifer about Groundwater Dependent Ecosystems. Thus there is: • A need to identify GDE types that exist based on their degrees of dependency on groundwater. • A need to classify the GDEs using a PFTconcept. • To compile a trait (morphological, phenological and physiological) database for TMG aquifer GDEs.

La mer Méditerranée est un hotspot de biodiversité sous diverses influences où plusieurs perturbations agissent en synergie: réchauffement climatique, perte d'habitats et surpêche menacent la biodiversité marine et perturbent les équilibres écosystémiques. Afin d'assurer une gestion durable des écosystèmes marins côtiers, conformément aux prérogatives de l'Approche Ecosystémique des Pêches, il est nécessaire d'étudier les conséquences de ces perturbations sur les populations exploitées. Or, malgré la multiplicité des études relatives au changement global en Méditerranée, les conséquences écosystémiques de ces changements demeurent mal connues. Dans cette thèse, le Golfe de Gabès a été choisi comme modèle d'étude en raison des nombreuses perturbations qui y sont rencontrées et qui en font l'archétype de tendances plus généralisées en Mer Méditerranée. Cette thèse se propose d'abord de replacer l'écosystème du Golfe de Gabès dans son contexte biogéographique à travers l'étude de la phylobiogéographie des assemblages des poissons côtiers méditerranéens et la modélisation de la structure et du fonctionnement de l'écosystème du Golfe de Gabès. Par la suite, nous proposons de modéliser, en utilisant des modèles de niches écologiques, les modifications potentielles futures des assemblages biogéographiques d'espèces exploitées soumises aux changements climatiques et à la perte d'habitat, ainsi que les conséquences trophiques de ces modifications. En prenant en compte la taxonomie et l'histoire évolutive des espèces, nous avons mis en évidence le niveau de séparation entre les assemblages méditerranéens en proposant une nouvelle délimitation biogéographique du plateau continental. Par ailleurs, l'exploration des dissimilarités phylogénétiques à l'échelle des côtes tunisiennes a mis en évidence quatre zones biogéographiques majeures présentant une faible congruence avec le zonage adopté pour la gestion de la pêche en Tunisie. Les projections des futures aires de répartition des 60 principales espèces exploitées du Golfe de Gabès, grâce à l'implémentation du modèle climatique NEMOMED8, révèlent que pour la fin du siècle, 34 espèces pourraient contracter leurs aires de répartition parmi lesquelles 12 espèces pourraient s'éteindre à l'échelle du Golfe. Par ailleurs, en combinant des scénarios de régression d'herbier et de changement climatique, les projections montrent que les magnitudes des modifications d'aires de répartition induites par le changement climatique sont plus larges que celles résultant de la perte d'habitat. La mise en place d'un modèle trophique Ecopath nous a permis de décrire la structure et le fonctionnement de l'écosystème du Golfe de Gabès et de le comparer avec d'autres écosystèmes méditerranéens exploités. Ce modèle a intégré un large éventail d'espèces depuis le phytoplancton jusqu'aux top-prédateurs ainsi que les principales activités de pêche opérant dans la zone. Les résultats du modèle mettent en évidence que le chalutage benthique est l'activité ayant les conséquences écosystémiques les plus étendues avec un fort impact sur certaines espèces démersales exploitées. Enfin, pour étudier les conséquences trophiques des modifications des distributions spatiales des espèces exploitées, nous avons reconstruit les réseaux trophiques au sein des assemblages d'espèces en nous fondant sur la relation positive liant la taille du prédateur à celle de sa proie. Nous avons ainsi pu prédire les réseaux trophiques actuels et projeter les modifications potentielles de leurs structures. Nous avons constaté qu'une grande partie du Golfe pourrait connaître une augmentation de la connectance et un allongement des voies trophiques moyennes qui s'accompagnent d'une diminution du nombre de proies par prédateur et du nombre de prédateurs par proie. Cette thèse est une ouverture vers la compréhension du rôle de la biodiversité dans le maintien du fonctionnement des écosystèmes. / The Mediterranean Sea is a marine biodiversity hot spot highly affected by several sources of disturbances interacting synergistically: global warming, habitat loss and overfishing threaten marine biodiversity and disrupt the ecosystem balance. To ensure a sustainable management of coastal marine ecosystems according to the Ecosystem Approach to Fisheries, it is necessary to study the ecosystem responses to these disturbances. However, despite the variety of global change studies in Mediterranean areas, ecosystems responses to these changes remain poorly understood and particularly at the southern part of the Mediterranean Sea. In this PhD thesis, the Gulf of Gabes was chosen as study area since it is one of the most affected regions by global change which makes it a mesocosm model of more regional patterns that occur in the Mediterranean Sea. In this study, as a first step, we replaced the Gulf of Gabes in its biogeographic and ecosystem regional context. This was achievied through a phylogenetic-based delineation of biogeographical species pools of coastal Mediterranean fishes and using an ecosystem model to describe its structure and functioning in comparison with other Mediterranean ecosystem model properties. We therefore projected potential future geographic ranges and assemblages composition of biogeographical exploited species pool according to global warming and habitat loss scenarios. Then we assessed their effects on food web structure. Taking into account the taxonomy and inter-species evolutionary relationships, we generate a new bioregionalisation of the continental shelf based on the turnover of lineages. Our results showed that climate is the major driver of species distribution and assemblage's composition. In addition, the exploration of phylogenetic dissimilarity across the Tunisian coast highlighted four major biogeographic areas showing a low spatial congruence with zoning used for fisheries management in Tunisia.Projected range shifts of the 60 main exploited species of the Gulf of Gabes through the implementation of a new climate model (NEMOMED8) revealed that, by the end of the century, 34 species could contract their ranges including 12 species that could become locally extinct across the Gulf of Gabes. Furthermore, by combining Posidonia meadows loss scenarios and climate change projections, our results showed that the magnitudes of the changes range induced by climate change are larger than those resulting from the loss of habitat.The Ecopath mass-balance model allowed us to describe the structure and functioning of the ecosystem of the Gulf of Gabes in comparison with other Mediterranean ecosystems. These models encompass the entire trophic spectrum from phytoplankton to higher trophic levels as well as the main fishing activities in the area. The model results showed that, among the fishing activities studied, bottom trawling was identified as the activity having the widest-ranging impacts across the different functional groups and the largest impacts on some commercially-targeted demersal fish species. Finally, to study the effects of species range shift on food web structure, we used a new methodology to infer trophic interactions between species. Based on the robust relationship between the size of prey and predators, we predicted the current food webs and project potential changes in their structures. We found that a significant portion of the Gulf of Gabes would face an increase of connectance and an extension of trophic pathways in parallel with a decrease in the number of prey per predator and the number of predators per prey. This PhD thesis paves the way towards the understanding of the role of biodiversity in maintaining ecosystem functioning.

Despite early initiatives during the 1960s and 1970s, and continuing efforts ever since, the Baltic Sea remains in poor condition. The Helsinki Commission (HELCOM) is the governing body tasked with protecting the marine environment from further deterioration through intergovernmental collaboration between the Baltic Sea states and the EU. In 2007, HELCOM launched a new tool – the Baltic Sea Action Plan (BSAP), of which the so-called ecosystem approach is a cornerstone. However, how and why the BSAP reform was launched, and also what consequences such management reforms can have for transboundary resource management, is unknown. By using institutional theory, organizational theory and the advocacy coalition framework, in combination with content analysis of official documents derived from HELCOM, this thesis argues that the BSAP is the end result of a gradual process of change within institutional structures and actor beliefs. This thesis also shows that HELCOM's capacity to detect, process, and react in response to changes in its regulatory objective has not changed as a consequence of the BSAP. In contrast to earlier research, it seems HELCOM responds better to slow and opaque changes than to quick and visible ones. Finally, by comparing HELCOM with two other similar cases, the thesis shows that HELCOM's adaptive capacity could be improved in line with the recommendations of the ecosystem approach. This thesis illustrates the importance of studying the emergence of new tools for governing transboundary resources from several theoretical perspectives. The thesis uses an innovative quantitative content analysis and concludes that new methods might be required to enable such studies. The different perspectives used here give various explanations concerning the causes and consequences of the BSAP. In a future Baltic Sea, where environmental changes are likely to be abrupt, a multitude of understandings regarding the governance of the Baltic Sea will be crucial. / <p>At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 2: Submitted. Paper 3: Submitted. Paper 4: In press.</p>

Holistic studies of mammalian life history factors and their consequences on population demography require an intensive, multifaceted field methodology and effort over long temporal scales. A 25-year longitudinal mark-recapture experiment on southern elephant seals, Mirounga leonina, at Subantarctic Marion Island provide such a foundation for demographic analyses and relevant methodology advancement. Two gaps in the methodology related to life history and population demographic research are, the absence of large samples of known mass individuals, and an inability to identify mother-pup relatedness. A novel three-dimensional photogrammetric technique is designed here that allows for mass estimation of large samples of southern elephant seals in the field. An effective temporary marking technique for unweaned pups is implemented that allows for identification of large samples of pups with known mothers prior to the maternal bond being severed at weaning. These known pups can then be marked with more robust tags and relatedness information is preserved long-term. Thus, mass estimates can now be applied as covariates in modelling analyses to address questions of, for example, maternal investment, kinship associated behaviour, and the consequences thereof on survival and reproductive parameters. The state change in the Marion Island southern elephant seal population from decrease to stabilisation/increase is shown to have resulted from improved survivorship in both juvenile and adult female age classes. Male seals of all ages did not indicate improved survivorship following the period of decline. The inflexion in survivorship is identified as 1994, whence improved survivorship of juvenile seals preceded that of young adult females. This inflexion in survivorship is postulated to have resulted in a population trend inflexion around 1998. Female southern elephant seals do not show evidence of actuarial senescence, but reproductive senescence is apparent after 12 years of age. A longterm reproductive cost (reduced breeding effort) is associated with early primiparity (age three) as compared with later primiparity (4- 5- or 6-year-old). The mean proportion of 3-year-old breeders has not increased after 1994 as has been hypothesized in previous studies. Contrary to previous assumptions, females do not as a rule breed every year. Annually interrupted breeding efforts are more common than consecutive breeding efforts. No difference in the proportions of interrupted versus uninterrupted breeding efforts was identified between periods of population decline and stabilisation/increase. Longevity as predicted by survival estimates exceeds the observed frequencies. This study provides unique longevity and fertility schedules for the species. The improved survivorship, reproductive senescence and breeding schedules of female southern elephant seals in this population provide groundwork for reevaluation of previous studies and their conclusions. The addition of relatedness and body condition information will allow for sophisticated multistate modelling of population demography in future studies. However, analytical procedures and techniques employed need to be meticulously designed and thoroughly thought through to avoid mis-interpretation of biological data. In addition to a multistate single species analytical approach, the importance of an ecosystem approach to species population demographic studies is highlighted through the augmenting of data on relevant potential drivers of population change, such as killer whales, Orcinus orca. / Thesis (PhD)--University of Pretoria, 2009. / Zoology and Entomology / unrestricted