As the biomass of jellyfish (medusae of the Scyphozoa and Hydrozoa) has risen in numerous locations worldwide, awareness of their potential to exert a controlling influence on marine ecosystems and hinder the recruitment of fish stocks has increased. Medusae are capable of intensive, size–selective, predation on zooplankton, which may alter the composition of the plankton community. Jellyfish are often found in dense layers, up to hundreds of metres thick, which can extend horizontally for hundreds of kilometres. Such aggregations may benefit specialist feeders, such as turtles, that rely upon jellyfish for food and those fish that are able to find refuge under the jellyfish umbrellas. Nonetheless, the predominance of jellyfish in pelagic ecosystems is not generally viewed as desirable; in fact, this situation has been portrayed as the result of pollution and overexploitation of otherwise productive seas. However, jellyfish are sensitive indicators of environmental change, and their populations appear to respond to climatic fluctuations, so jellyfish warrant study for their intrinsic ecosystem role particularly given present concerns over climate change. With growing acceptance that fishery management should take an holistic ‘ecosystem approach’, knowledge of the interactions between jellyfish, fisheries and climate may be vital in progression towards the goal of ecosystem–based sustainable management of fisheries. Unfortunately, due to their gelatinous nature, medusae are difficult to sample using conventional netting techniques and data on changes in distribution and abundance are consequently sparse. Recent studies have demonstrated that medusae can be detected acoustically and that this technique could provide a rapid and cost–effective estimate of their biomass and distribution. This thesis reports my endeavour to demonstrate the ecosystem role of medusae and to develop acoustic techniques to monitor their biomass. Through regession analyses, I link the abundance of medusae (Aurelia aurita, Cyanea lamarckii, and Cyanea capillata) in regions of the North Sea to climatic fluctuations, as quantified by the North Atlantic Oscillation Index, and show that medusae may be important indicators of regional ecosystem change. The mechanisms linking climatic fluctuations to ecosystem changes are explored via a correlative modelling approach using General Additive Models; I show that the mechanisms are location dependent and explainable in terms of direct, rapidly responding (intra–annual) influences (surface warming, river run–off, and wind–driven mixing and advection) and longer–term (interannual) oceanographic responses (changes in circulation currents i.e. the northward extent of the gulf stream and relative strength of inflow into the North Sea of the North Atlantic current, Continental Shelf Jet and Arctic waters). I present correlative evidence for a detrimental impact by Aurelia aurita on herring 0–group recruitment, once the influence of interannual change in herring spewing stock biomass on recruitment is factored out through modelling with a Ricker stock–recruitment relationship. Similarly, a commensal relationship between whiting and Cyanea spp. medusae is shown to improve North Sea whiting survival to the 1–group. In progress towards the automated acoustic identification of species, I have developed an in situ discrimination tool that can distinguish between echoes from: Aequorea aequorea; Chrysaora hysoscella; clupeid fish (sardine, anchovy and round herring); and horse mackerel/Cape hake. The technique relies upon characteristic differences in echo strength between frequencies, which are determined for each jellyfish species and finfish group using combined multifrequency acoustic and pelagic trawl samples. This method has facilitated the world’s first acoustic–based estimate of jellyfish biomass in the Namibian Benguela Sea. The 12.2 million tonnes of biomass of medusae (Aequorea aequorea and Chrysaora hysoscella) in the Namibian Benguela Sea was found to be greater than the combined biomass, 3.6 million tonnes, of commercially important fish (horse mackerel, Cape hake, sardines, anchovy, and round herring) in the same area. These results suggest that medusae may have an important role in the Benguela ecosystem that has previously been overlooked and that their biomass should be monitored.

Nausithoe aurea Silveira & Morandini, 1997 é uma espécie metagenética e dióica com fecundação externa. Os oócitos são liberados continuamente (55 dias em laboratório), porém com grandes variações no número a cada dia. No desenvolvimento embrionário a clivagem, após o estágio de 8 células, passa de holoblástica e igual para pseudoespiral. A gastrulação ocorre por ingressão multipolar e inicia-se aproximadamente 24 horas após a fecundação. A estrutura histológica geral das gônadas assemelha-se a outros Scyphozoa, onde os gonócitos proliferam a partir da gastroderme, migram e diferenciam-se na mesogléia. Na gônada masculina as células germinativas formam camadas razoavelmente distintas e constituem folículos testiculares. Na gônada feminina os oócitos surgem da zona germinativa na gastroderme e apresentam um gradiente de maturação a partir deste ponto (cortes no sentido oral-aboral). Os oócitos encontram-se livres na mesogléia da gônada, sem associação com outras células. A relação espacial entre a musculatura circular, as gônadas e o sulco coronal, é uma característica a ser usada na sistemática do gênero Nausithoe Kölliker, 1853. / Nausithoe aurea Silveira & Morandini, 1997 is a metagenetic and dioecious species with external fertilization. The oocytes are released continuously (55 days in laboratory), but with great variations in the daily number. In the embryonic development the cleavage, after the 8 cells stage, changes from holoblastic and adequal to pseudospiral. The gastrulation occurs through multipolar ingression and begin 24 hours after fertilization. The general histological structure of the gonads resembles other Scyphozoa, in which the gonocytes proliferate from the gastrodermis, migrate and differentiate in the mesoglea. In the male gonad the germ cells are arranged in distinctive layers and form follicles (cysts). In the female gonad the oocytes develop from the germinative zone in the gastrodermis and present a maturing gradient from this point on (oral-aboral sections). The oocytes are free in the gonad mesoglea, without association to any cell. The spatial relation of the coronal musculature, gonads and coronal groove, is a character to be used in the systematics of the genus Nausithoe Kölliker, 1853.

Perçues jusqu’au XIXe siècle comme des masses gélatineuses aux propriétés urticantes, les méduses ont été classées dans le groupe des zoophytes, organismes intermédiaires entre les animaux et les végétaux. Les savants s’en sont alors servis pour démontrer la continuité entre les êtres vivants végétaux et animaux et elles sont devenues des arguments essentiels dans l’établissement de l’échelle des êtres. A partir du XIXe siècle, on découvre, en particulier grâce à la microscopie, la complexité de leur anatomie, ce qui permet enfin de les caractériser de manière positive. Au milieu du XIXe siècle, on met en évidence les différentes phases de leur cycle de vie et l’organisation en colonie de certaines méduses. Les méduses deviennent alors l’un des principaux centres d’intérêt des zoologistes et des embryologistes qui cherchent à trouver la signification évolutive des différentes étapes de leur développement. Le terme de méduse apparaît alors pour désigner un de leurs stades de vie. En parallèle de cette histoire conceptuelle, les différentes étapes de cette classification ont été marquées par des difficultés d’étude qui ont fait que les méduses constituaient un des rares groupes non définis par des caractères positifs à la fin du XVIIIe siècle. En effet, si les expéditions scientifiques ont permis de récupérer de nombreux échantillons, bien vite s’est posé le problème de leur conservation. Face aux difficultés de maintenir leur morphologie et leurs couleurs après leur prélèvement, les images naturalistes de méduses sont donc devenues des objets d’étude essentiels dans la connaissance et la classification de ces organismes. Ces images donnent un reflet de l’évolution conceptuelle et technique, qui a accompagnée la classification des méduses / Perceived until the 19th century as gelatinous masses with stinging properties, jellyfish were classified in the group of zoophytes, intermediate organisms between animals and plants. Scientists then used it to demonstrate continuity between plant and animal living beings and became essential arguments in establishing the scale of beings. From the nineteenth century, we discover, particularly through microscopy, the complexity of their anatomy, which finally allows to characterize them positively. In the mid-nineteenth century, we highlight the different phases of their life cycle and the colony organization of some jellyfish. Jellyfish become one of the main interests of zoologists and embryologists who seek to find the evolutionary significance of the different stages of their development. The term jellyfish then appears to designate one of their life stages. In parallel with this conceptual history, the various stages of this classification were marked by study difficulties which made jellyfish one of the few groups not defined by positive characters at the end of the eighteenth century. Indeed, if the scientific expeditions allowed to recover many samples, quickly the problem of their conservation was posed. Faced with the difficulties of maintaining their morphology and their colors after their collection, the naturalistic images of jellyfish have thus become essential objects of study in the knowledge and classification of these organisms. These images give a reflection of the conceptual and technical evolution, which accompanied the classification of jellyfish

Background: Collagens of marine origin are applied increasingly as alternatives to mammalian collagens in tissue engineering. The aim of the present study was to develop a biphasic scaffold from exclusively marine collagens supporting both osteogenic and chondrogenic differentiation and to find a suitable setup for in vitro chondrogenic and osteogenic differentiation of human mesenchymal stroma cells (hMSC). Methods: Biphasic scaffolds from biomimetically mineralized salmon collagen and fibrillized jellyfish collagen were fabricated by joint freeze-drying and crosslinking. Different experiments were performed to analyze the influence of cell density and TGF-β on osteogenic differentiation of the cells in the scaffolds. Gene expression analysis and analysis of cartilage extracellular matrix components were performed and activity of alkaline phosphatase was determined. Furthermore, histological sections of differentiated cells in the biphasic scaffolds were analyzed. Results: Stable biphasic scaffolds from two different marine collagens were prepared. An in vitro setup for osteochondral differentiation was developed involving (1) different seeding densities in the phases; (2) additional application of alginate hydrogel in the chondral part; (3) pre-differentiation and sequential seeding of the scaffolds and (4) osteochondral medium. Spatially separated osteogenic and chondrogenic differentiation of hMSC was achieved in this setup, while osteochondral medium in combination with the biphasic scaffolds alone was not sufficient to reach this ambition. Conclusions: Biphasic, but monolithic scaffolds from exclusively marine collagens are suitable for the development of osteochondral constructs.

Nausithoe aurea Silveira & Morandini, 1997 é uma espécie metagenética e dióica com fecundação externa. Os oócitos são liberados continuamente (55 dias em laboratório), porém com grandes variações no número a cada dia. No desenvolvimento embrionário a clivagem, após o estágio de 8 células, passa de holoblástica e igual para pseudoespiral. A gastrulação ocorre por ingressão multipolar e inicia-se aproximadamente 24 horas após a fecundação. A estrutura histológica geral das gônadas assemelha-se a outros Scyphozoa, onde os gonócitos proliferam a partir da gastroderme, migram e diferenciam-se na mesogléia. Na gônada masculina as células germinativas formam camadas razoavelmente distintas e constituem folículos testiculares. Na gônada feminina os oócitos surgem da zona germinativa na gastroderme e apresentam um gradiente de maturação a partir deste ponto (cortes no sentido oral-aboral). Os oócitos encontram-se livres na mesogléia da gônada, sem associação com outras células. A relação espacial entre a musculatura circular, as gônadas e o sulco coronal, é uma característica a ser usada na sistemática do gênero Nausithoe Kölliker, 1853. / Nausithoe aurea Silveira & Morandini, 1997 is a metagenetic and dioecious species with external fertilization. The oocytes are released continuously (55 days in laboratory), but with great variations in the daily number. In the embryonic development the cleavage, after the 8 cells stage, changes from holoblastic and adequal to pseudospiral. The gastrulation occurs through multipolar ingression and begin 24 hours after fertilization. The general histological structure of the gonads resembles other Scyphozoa, in which the gonocytes proliferate from the gastrodermis, migrate and differentiate in the mesoglea. In the male gonad the germ cells are arranged in distinctive layers and form follicles (cysts). In the female gonad the oocytes develop from the germinative zone in the gastrodermis and present a maturing gradient from this point on (oral-aboral sections). The oocytes are free in the gonad mesoglea, without association to any cell. The spatial relation of the coronal musculature, gonads and coronal groove, is a character to be used in the systematics of the genus Nausithoe Kölliker, 1853.

Les Pertuis Charentais sont un site d’écosystèmes interconnectés où les courants marins jouent un rôle déterminant. Un modèle de marée à haute résolution a été développé au cours de cette thèse pour comprendre et cartographier les traits principaux de la circulation hydrodynamique dans les Pertuis. Deux axes sont ainsi mis en avant dans cette étude. D’abord, un nouveau modèle de marées dans les Pertuis Charentais a été construit et validé à partir de différentes sources : données marégraphiques, données de courantomètres ADCP et images satellitaires. Une nouvelle approche de calibration de modèle de marée a été développée, basée sur la comparaison de la position de la ligne d’eau, frontière entre l’eau et la terre, avec celle prédite par le modèle. Puis dans un second temps, le transport et les agrégations en « bloom » de populations de méduses Rhizostoma, dont les proliférations et les échouages sont à l’origine de problèmes socio-économiques, ont été simulés numériquement. Des observations in situ ont permis de paramétrer le comportement de nage des méduses dans le modèle. Deux types de comportements des méduses, actif et passif ont été simulés. Les courants de marées en présence des forçages-type météorologiques ont été pris en compte. Les résultats indiquent que le comportement individuel de nage des méduses pourrait être une réponse adaptative aux facteurs abiotiques qui menacent la continuité de leur espèce mais que les courants marins restent la cause première de la formation des blooms. / The Pertuis Charentais are an interconnected ecosystems site where ocean currents play a key role. A high resolution tidal model was developed in this thesis in order to understand the main features of the hydrodynamic flows inside the Pertuis. Two topics were put forward in this study. First, a new tide model for the Pertuis Charentais was build up and validated by using different datasets: tide gauge records, measurements of currents by ADCP and satellite images. A new approach to model calibration was developed by comparing the observed position of the waterline, the boundary between land and water, with that predicted by the model. Secondly, the transport and bloom-like aggregation of the Rhizostoma jellyfish populations were simulated numerically. The jellyfish proliferation and stranding are a source of socio-economic problems. Two types of jellyfish behavior, active and passive were simulated. The tidal currents and typical meteorological forcing were taken into account. The results show that the individual behavior of swimming jellyfish is an adaptive response to abiotic factors for jellyfish survival.

Background: Collagens of marine origin are applied increasingly as alternatives to mammalian collagens in tissue engineering. The aim of the present study was to develop a biphasic scaffold from exclusively marine collagens supporting both osteogenic and chondrogenic differentiation and to find a suitable setup for in vitro chondrogenic and osteogenic differentiation of human mesenchymal stroma cells (hMSC). Methods: Biphasic scaffolds from biomimetically mineralized salmon collagen and fibrillized jellyfish collagen were fabricated by joint freeze-drying and crosslinking. Different experiments were performed to analyze the influence of cell density and TGF-β on osteogenic differentiation of the cells in the scaffolds. Gene expression analysis and analysis of cartilage extracellular matrix components were performed and activity of alkaline phosphatase was determined. Furthermore, histological sections of differentiated cells in the biphasic scaffolds were analyzed. Results: Stable biphasic scaffolds from two different marine collagens were prepared. An in vitro setup for osteochondral differentiation was developed involving (1) different seeding densities in the phases; (2) additional application of alginate hydrogel in the chondral part; (3) pre-differentiation and sequential seeding of the scaffolds and (4) osteochondral medium. Spatially separated osteogenic and chondrogenic differentiation of hMSC was achieved in this setup, while osteochondral medium in combination with the biphasic scaffolds alone was not sufficient to reach this ambition. Conclusions: Biphasic, but monolithic scaffolds from exclusively marine collagens are suitable for the development of osteochondral constructs.

No description available.