Most marine invertebrates have a complex life cycle involving a benthic adult phase, and a planktonic larval phase. The process whereby tiny larvae are able to locate, settle and metamorphose in a habitat where juveniles are then capable of successfully establishing themselves is a key stage in the life cycle and a central theme of current marine research. Bacterial biofilms are an important settlement cue for many larvae, and it appears that particular strains within environmental communities may be responsible for the inducing ability of some biofilms. The focus of this thesis is the importance of biofilms for larval settlement of the blacklip abalone Haliotis rubra and the sea urchin Heliocidaris erythrogramma. Larval development of the sea urchin Centrostephanus rodgersii was also examined, but this species was problematic for a larval settlement study. H. rubra larval settlement occurred in response to several macroalgal species. Biofilmed (but otherwise abiotic) surfaces did not induce settlement of H. rubra larvae and reduction of surface films of bacteria and diatoms on inducing algae did not reduce the settlement response. Macroalgae, particularly green algal species, may play an important role in the recruitment of H. rubra larvae in the field and can be used to induce settlement in hatcheries. H. erythrogramma settled in response to a range of surfaces with highest settlement on coralline algae. Settlement was reduced by autoclaving plants and treating plants with antibiotics. Molecular and culture based analysis revealed a shift in microbial community structure between plants treated with antibiotics and unmanipulated plants. Many bacterial strains, dominated by the genera Pseudoalteromonas, Shewanella and Vibrio, induced larval settlement. Three probes targeting Pseudoalteromonas, Shewanella and Vibrio were developed for CARD-FISH, enabling quantification of these genera in biofilms on algae. The three genera were found in highest numbers on coralline algae and in variable numbers on the surfaces of other algae. Recruitment of H. erythrogramma also occurs in highest numbers on coralline algae, and in low amounts on co-occurring algae. This is the first example demonstrating that bacteria that induce settlement in the laboratory are also present in the juvenile recruitment habitat.

The papers presented in this thesis represent my contributions to the empirical study of marine biological resources. This research has adopted the same experimental approach to: (i) develop scientifically validated techniques to solve specific problems; (ii) use these techniques to detect patterns and form conceptual models about the processes that may have caused them; (iii) do manipulative field experiments to support or refute hypotheses derived from these models; (iv) use these results to develop new models and hypotheses and to test them in new experiments; and (v) recommend, where appropriate, changes to the management of the resources examined. A rigorous, empirical approach is the common feature throughout my research (in its overall direction and subject-to-subject execution) and represents one of the few attempts to adopt such an approach across the three fields in which I have worked: (1) the ecology of underwater kelp systems; (2) the biology of and fishery for a commercially exploited crab; and (3) solving by-catch problems in commercial trawl fisheries.

Thesis--Zurich. / Includes bibliographical references (p. v-vi).

Bibliography : leaves 127-135

<p>Rates of habitat alteration and degradation are increasing worldwide due to anthropogenic influence. On coral reefs, the loss of live coral reduces structural complexity while facilitating algal increase. In many coastal lagoons seagrass and corals are cleared to make room for cultivated macroalgae. This thesis deals with reef and lagoon habitat structure and how fish assemblage patterns may be related to physical and biological features of the habitat. It further examines assemblage change following habitat disturbance. Four studies on East African coral reefs concluded that both the abundance and species richness of recruit and adult coral reef fish were largely predicted by the presence of live coral cover and structural complexity (Papers I-III, VI). Typically, recruits were more selective than adults, as manifested by limited distributions to degraded sites. Paper VI compared short- and long-term responses of fish assemblages to the 1997-1998 bleaching event. The short-term response to coral mortality included the loss of coral dwelling species in favour of species which feed on algae or associated detrital resources. Counterintuitively, fish abundance and taxonomic richness increased significantly at one of two sites shortly after the bleaching. However, the initial increase was later reversed and six years after the death of the coral, only a limited number of fish remained. The influence of fleshy algae on fish assemblages was studied in algal farms (Paper IV), and examined experimentally (Paper V). The effects of algal farming in Zanzibar were significant. Meanwhile, manually clearing algal-dominated patch reefs in Belize from macroalgae resulted in short-term increases of abundance, biomass and activity of a few species, including major herbivores. The findings of this thesis demonstrate the significance of habitat as a structuring factor for tropical fish assemblages and predicts that coral death, subsequent erosion and algal overgrowth may have substantial deleterious impacts on fish assemblage composition, abundance and taxonomic richness, with recovery being slow and related to the recovery of the reef framework.</p>

<p><strong>Abstract</strong></p><p>The European eel (<em>Anguilla anguilla</em>) migrates to the Sargasso Sea to spawn. Even though the biology of <em>A. anguilla </em>leptocephali in the Sargasso Sea has been studied for several decades, information regarding their diet has remained unknown until now. Previous dietary studies concerning other species of leptocephali in the Pacific Ocean have been limited to the recognition of identifiable prey remains amongst gut contents. Hence, in this study a molecular approach relying on the detection of prey DNA amongst gut contents was used to study dietary profiles of <em>A. anguilla</em> leptocephali in the Sargasso Sea.</p><p> </p><p>Leptocephali were collected during the circumglobal Galathea 3 expedition in spring 2007 to the Sargasso Sea. DNA extracted from gut contents were PCR amplified using universal primers targeting the nuclear 18S rRNA gene. In order to separate eel amplicons from prey amplicons, PCR products were analyzed by denaturing gradient gel electrophoresis (DGGE). Furthermore, clone libraries were constructed using universal primers targeting a portion of the 18S rRNA and mitochondrial COI gene, respectively. In total, the gut contents of 78 leptocephali were screened by DGGE.</p><p> </p><p>A diverse array of eukaryotic taxa was identified, hence demonstrating the applicability of a universal PCR- DGGE approach to study gut contents of leptocephali. The results presented here show, for the first time, that young stages of <em>A. anguilla</em> leptocephali feed on a large variety of zooplankton of which many were gelatinous (e.g. Hydrozoa, Thaliacea and Ctenophora). Several of the identified taxa also constitute important parts of the Sargasso Sea zooplankton community and are of size ranges (adult or larval stages) that made them reasonable as leptocephali prey.</p>

<p>The purpose of this work has been to investigate the ultimate capacities of aluminium plates. The aluminium plates are supposed to be part of a marine structure. Their behaviour has been explored by taking advantage of non-linear finite element simulations. The loading conditions included axial compression, transverse compression, pure shear loading, axial compression in combination with transverse compression and axial compression in combination with shear loading.</p><p>Different patterns of heat affected zones have been studied with particular attention on conventionally welded plates and extruded, welded plates. The plates have been given realistic boundary conditions in addition to boundary conditions believed to represent the extremities in plate collapse behaviour. The initial deflection patterns chosen, were generally conservative, and the variations in collapse capacities for different initial deflection patterns have been investigated. The initial deflection amplitudes were systematically varied to cover all values of the initial deflection amplitudes likely to occur.</p><p>In addition to studying different patterns of the heat affected zones, systematic variations of the breadths of the heat affected zones have been performed. Systematic variations in the magnitudes of the residual stresses and systematic variations of the reductions of the 0.2 percent tensile proof stresses in the heat affected zones have also been carried out. Three different aluminium alloys were studied. They were believed to represent a high, medium and low utilised aluminium alloy. The aspect ratio of the plates was varied to cover both plates that were completely square to plates with a length equal to five times the breadth of the plates.</p><p>It was found that axially loaded plates with heat affected zones along loaded edges had lower ultimate capacities than plates with heat affected zones along unloaded edges, and if the plates had heat affected zones along loaded edges, having additional heat affected zones along unloaded edges did not alter the buckling capacities. The reduction in ultimate capacity could be modelled to vary linearly with the breadth of the heat affected zones, and the reduction in ultimate capacity could be modelled to vary linearly with the relationship between the value of the 0.2 percent tensile proof stress in the heat affected zones and the 0.2 percent tensile proof stress of the base material.</p><p>The ultimate capacities of transversally loaded plates could be found as the sum of a square plate and a plate strip, even if the plates contained heat affected zones. Square plates and plate strips with relevant patterns of heat affected zones had to be employed. Biaxial interaction curves showed a considerable slenderness dependence for all values of the aspect ratio investigated. The biaxial interaction curves were only slightly affected by introduction of different patterns of heat affected zones. The stress corresponding to equal elastic and plastic strain was better suited as the normalising stress than the more commonly used 0.2 percent tensile proof stress. One design curve could be used to represent all the different aluminium alloys investigated. Changing the aluminium alloy did not change the shape of the biaxial interaction curves.</p><p>Based on the detailed study of the collapse behaviour of aluminium plates carried out, and established practice, new ULS design formulas for axial compression, transverse compression, pure shear loading, axial compression in combination with transverse compression and axial compression in combination with shear loading were proposed. The new design formulas accounted for reductions in ultimate capacities due to heat affected zones, including heat affected zones along loaded edges. They took full advantage of non-linear residual strength for slender plates; and the slenderness dependence and aspect ratio dependence for biaxial interaction curves were systematically incorporated.</p>

<p>The present thesis deals with ultimate strength and collapse analysis of ship structures. Within this are, the attention is directed towards simple and efficient nonlinear finite element models for stiffened plate panels in ship structures. Several types of Morley elements are investigated and two are selected for further development. These triangular elements assume constant stress distribution over the element area. </p><p>The first element considered is a nonlinear facet shell element which is valid within moderate rotations. Its elastic formulation has been proposed earlier. In this work, the element matrices are extended to account for material plasticity. The second element, is a displacement-based curved element which undergoes arbitrary large displacements and rotations. The discrete equilibrium equations for this element are re-derived so as to make them more efficient with standard Newton-Raphson solution procedures. </p><p>Material plasticity formulation using through-the thickness integration as well as resultants plasticity is presented. The evolution laws are derived from the natural laws of thermodynamics, and a return mapping algorithm with a backward Euler difference scheme is used for a solution of the evolution equations. The plasticity computations involve a solution of a single scalar yield surface for the plasticity multiplier. By performing the matrix algebra analytically, simple and explicit expressions are derived. These equations reduce the computational costs remarkably.</p><p>Numerical examples, mostly selected from well-know benchmark problems, are presented to demonstrate the performance of the proposed formulations. Very good agreement is obtained when compared with published results. In addition, typical problems for ultimate strength and collapse analysis of ship hull-girder are analyzed. These include plate girders, stiffened plate panels, as well as a cruciform element. The results show good agreement not only with those obtained from commercial finite element programs, but also from the experimental observations. For stiffened plate panels, comparison is made with DNV design rules, which is found to give non-conservative estimates for some load conditions.</p><p>Finally, a study on multi-span stiffened panels is performed so as to compare the estimates provided by the conventional single span model. It is observed that the conventional model provides conservative estimates, and the effect of transverse frames is especially significant on the finite element model of stiffened panels. </p>

Graduation date: 1983

Graduation date: 1979