The pike (Esox lucius) is a major predator and top-down regulator in the Baltic Sea where it exists in two sympatric forms. One spawn in streams and rivers and the other one spawn in the sea. During the last decades, the habitats for both of these forms have developed in a negative way. In some freshwater systems, up to 90 % of the water areas have disappeared, mainly through drainage and straightening of watercourses for agricultural purposes. In the sea, reproduction habitats decrease due to construction of harbours and human activities that create disturbances. The perhaps largest single factor negatively affecting recruitment of pike in the sea is the eutrophication. Bottoms are overgrown with filamentous algae and shallow bays are covered with dense Phragmites belts decreasing the habitats suitable for spawning. Further on, a predator on egg and fish larvae, the three-spined stickleback (Gasterosteus aculeatus) has increased in abundance. It is difficult to restore and enhance pike production in the sea and probably the only economically viable alternative is to make restorations in freshwater. However, there is a limited knowledge about the freshwater spawning pike in the Baltic Sea. Thus in this thesis I, together with my coauthors, set out with an aim to increase the knowledge base regarding anadromous pike behaviour. We found that pike of natal freshwater origin were common in the Baltic Sea. Through Sr:Ca studies in otoliths, about 45 % of the pike were interpreted to be of freshwater origin. The majority of the pike had emigrated out of freshwater at a length below 6 cm. These results indicate that freshwater recruitment is successful, contrasting the vast areas available for spawning in the sea. This creates incitements that restoration measures in these watercourses could have a significant effect on the pike population in the Baltic Sea. Further, in four streams running out in the Baltic Sea, more than three thousand pike were marked to study spawning migration. About 30-40 % returned to the same river the subsequent year. Most of the pike used the lower parts of the stream for spawning. The homing of pike to a watercourse indicate that freshwater pike in the Baltic Sea consist of specific populations and this is crucial information when taking decisions on fish restoration measures. Three wetlands adjacent to streams were restored for pike production. The most successful restoration involved minimal digging, with flooded grasslands providing optimal conditions for spawning. The first spawning season after restoration increased the pike production hundredfold. In conclusion, the anadromous pike are numerous in the Baltic Sea. To compensate for the decline in pike populations in the sea, “pike-factories” created along the coastline are probably the most justifiable option.

<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 thesis addresses the hydrodynamic forces on cylinders where the angle between incoming flow and the cylinder axis, the angle of attack, is low. Measured results for a rigid cylinder with length to diameter ratio of 40 towed at both constant angle of attack and oscilllating in the transverse direction are used to discuss the applicability of suggested methods like the cross flow or the 2D+t principle. It is found that the longitudional flow do influence the transverse forces. The importance of the flow pattern initiated at the nose of the cylinder is clearly illustrated.</p><p>A combination of linear and quadratic dependence on the sine of the angle is used to model the response of a flexible cylinder with forced oscillation of the tow point. The result is compared to experimental result for a flexible cylinder with length to diameter ratio of 1100 and Reynolds numbers in and above the critical range. The cylinder is simulated in time domain with a Finite Element Method with second order elements. As an example of practical application of the model, the response of a part of a full scale streamer subject to irregular waves and a control device is investigated. In realistic sea states the response is found to be rather small, but not damped by the control device. </p>

<p>Large relative motions between the ship and the water may cause water shipping on the main deck. In this thesis, the fundamental features of water-on-deck phenomena are in vestigated, together with the "green" water loading on a deck house in the bow region. The studies are relevant for a stationary ship like a FPSO in head sea waves.</p><p>Potential flow theory is used to study numerically a nonlinear two-dimensional problem in a plane containing the ship's centerplane. The developed model is verified by various test cases, and validated by published as well as new experimental data.</p><p>The influence of wave parameters, ship motions and hull geometry is investigated. Relevance of three-dimensional effects is discussed.</p><p>Dedicated two-dimensional model tests have been performed, both to elucidate the fluid mechanics involved in the water shipping and to validate the numerical method. It is found that the water shipping starts in the form of a plunging wave hitting the deck. This could cause structural damages. Most often, the plunging is localized in the bow region and do not affect the main flow at a later stage. In a few cases, larger masses of water bluntly impacting with the deck have been observed. The latter is consistent with seldom observations reported in 3-D experiments, with large and steep waves plunging directly onto the deck. More often the water flow along the deck resembles the one subsequent to a dam breaking. Both types of events are investigated numerically. The impact pressures on a vertical wall in the bow area are measured and compare well with the boundary element method.</p><p>The reliability of a dam-breaking model and shallow-water approximation to study the propagation of water on the deck is examined. The former can only qualitatively describe the flow evolution.The latter can in principle be used but needs information from the exterior flow and, thus, the solution of the complete ship-waveinteraction problem.</p><p>Water impacts with a deck house in the bow area are studied in details. Use of a similarity solution for a water wedge hitting a rigid wall at 90º is compared with the fully numerical solution. The method predicts correctly the first stages of the impact with a smaller computational effort. Inuence of local flow conditions and wall slope on hydrodynamic loads is discussed. Importance of hydroelasticity is investigated in case of realistic structural parameters for the deck house. This shows a limited role of structural deformations in determining the maximum loads.</p>

<p>The objective of this thesis is to experimentally study different breaking waves cases. This is done by measuring in detail the free surface geometry and the internal kinematics of the waves as they approach breaking. Three principal wave cases were chosen for the study: A plunging breaker, a spilling breaker, and an intermediate breaker.</p><p>A major part of this work is the design, construction and building of a wave laboratory. The laboratory contains a glass wall waveflume which is 13.5m long, 1m deep and 0.6m wide, as well as equipment for measuring both the wave kinematics and geometry optically. The wave kinematics is measured using the Particle Image Velocimetry (PIV) method, while the wave profile geometry is measured using image analysis (space domain geometry), as well as standard wave gauges (time domain geometry).</p><p>The analysis of both the wave kinematics and geometry is done using parameters describing quantitatively important features in the wave evolution. The surface geometry is described using the commonly known zero-downcross parameters, and in addition, new parameters are suggested and used in the study, The kinematics are described by a set of four parameters suggested for the first time in this work. These parameters are: Velocity at the surface, velocity at the still water line (z = 0), mean velocity direction, and local wave number. The purpose of these parameters is to give a better understanding of the space and time domain development of the kinematics, and they appear to be a reasonable compromise between simplicity and accuracy.</p><p>The results presented here represents a thorough and detailed mapping of the breaking process. Much data is gathered and analysed, and throughout this thesis it is sought to present the data in the most intuitive way, so that other investigations may benefit from it. </p>

Large relative motions between the ship and the water may cause water shipping on the main deck. In this thesis, the fundamental features of water-on-deck phenomena are in vestigated, together with the "green" water loading on a deck house in the bow region. The studies are relevant for a stationary ship like a FPSO in head sea waves. Potential flow theory is used to study numerically a nonlinear two-dimensional problem in a plane containing the ship's centerplane. The developed model is verified by various test cases, and validated by published as well as new experimental data. The influence of wave parameters, ship motions and hull geometry is investigated. Relevance of three-dimensional effects is discussed. Dedicated two-dimensional model tests have been performed, both to elucidate the fluid mechanics involved in the water shipping and to validate the numerical method. It is found that the water shipping starts in the form of a plunging wave hitting the deck. This could cause structural damages. Most often, the plunging is localized in the bow region and do not affect the main flow at a later stage. In a few cases, larger masses of water bluntly impacting with the deck have been observed. The latter is consistent with seldom observations reported in 3-D experiments, with large and steep waves plunging directly onto the deck. More often the water flow along the deck resembles the one subsequent to a dam breaking. Both types of events are investigated numerically. The impact pressures on a vertical wall in the bow area are measured and compare well with the boundary element method. The reliability of a dam-breaking model and shallow-water approximation to study the propagation of water on the deck is examined. The former can only qualitatively describe the flow evolution.The latter can in principle be used but needs information from the exterior flow and, thus, the solution of the complete ship-waveinteraction problem. Water impacts with a deck house in the bow area are studied in details. Use of a similarity solution for a water wedge hitting a rigid wall at 90º is compared with the fully numerical solution. The method predicts correctly the first stages of the impact with a smaller computational effort. Inuence of local flow conditions and wall slope on hydrodynamic loads is discussed. Importance of hydroelasticity is investigated in case of realistic structural parameters for the deck house. This shows a limited role of structural deformations in determining the maximum loads.

The objective of this thesis is to experimentally study different breaking waves cases. This is done by measuring in detail the free surface geometry and the internal kinematics of the waves as they approach breaking. Three principal wave cases were chosen for the study: A plunging breaker, a spilling breaker, and an intermediate breaker. A major part of this work is the design, construction and building of a wave laboratory. The laboratory contains a glass wall waveflume which is 13.5m long, 1m deep and 0.6m wide, as well as equipment for measuring both the wave kinematics and geometry optically. The wave kinematics is measured using the Particle Image Velocimetry (PIV) method, while the wave profile geometry is measured using image analysis (space domain geometry), as well as standard wave gauges (time domain geometry). The analysis of both the wave kinematics and geometry is done using parameters describing quantitatively important features in the wave evolution. The surface geometry is described using the commonly known zero-downcross parameters, and in addition, new parameters are suggested and used in the study, The kinematics are described by a set of four parameters suggested for the first time in this work. These parameters are: Velocity at the surface, velocity at the still water line (z = 0), mean velocity direction, and local wave number. The purpose of these parameters is to give a better understanding of the space and time domain development of the kinematics, and they appear to be a reasonable compromise between simplicity and accuracy. The results presented here represents a thorough and detailed mapping of the breaking process. Much data is gathered and analysed, and throughout this thesis it is sought to present the data in the most intuitive way, so that other investigations may benefit from it.

The thesis addresses the hydrodynamic forces on cylinders where the angle between incoming flow and the cylinder axis, the angle of attack, is low. Measured results for a rigid cylinder with length to diameter ratio of 40 towed at both constant angle of attack and oscilllating in the transverse direction are used to discuss the applicability of suggested methods like the cross flow or the 2D+t principle. It is found that the longitudional flow do influence the transverse forces. The importance of the flow pattern initiated at the nose of the cylinder is clearly illustrated. A combination of linear and quadratic dependence on the sine of the angle is used to model the response of a flexible cylinder with forced oscillation of the tow point. The result is compared to experimental result for a flexible cylinder with length to diameter ratio of 1100 and Reynolds numbers in and above the critical range. The cylinder is simulated in time domain with a Finite Element Method with second order elements. As an example of practical application of the model, the response of a part of a full scale streamer subject to irregular waves and a control device is investigated. In realistic sea states the response is found to be rather small, but not damped by the control device.

Abstract The European eel (Anguilla anguilla) migrates to the Sargasso Sea to spawn. Even though the biology of A. anguilla 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 A. anguilla leptocephali in the Sargasso Sea.   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.   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 A. anguilla 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.