The advective motion of seawater governs the transport of almost everything, animate or inanimate, present in the ocean and those lacking the ability to outswim the currents have to follow the flow. This makes modelling of advective ocean transports a powerful tool in various fields of science where a displacement of something over time is studied. The present thesis comprises four different applications of ocean-transport modelling, ranging from large-scale heat transports to the dispersion of juvenile marine organisms. The aim has been to adapt the method not only to the object of study, but also to the available model-data sets and in situ-observations. The first application in the thesis is a study of the oceanic heat transport. It illustrates the importance of wind forcing for not only the heat transport from the Indian to the Atlantic Ocean, but also for the net northward transport of heat in the Atlantic. In the next study focus is on the particle-transport differences between an open and a semi-enclosed coastal area on the Swedish coast of the Baltic Sea. The modelled patterns of sedimentation and residence times in the two basins are examined after particles having been released from a number of prescribed point sources. In the two final studies the transport-modelling framework is applied within a marine-ecology context and the transported entities are larvae of some Scandinavian sessile and sedentary species and non-commercial fishes (e.g. the bay barnacle, the blue mussel, the shore crab and the gobies). The effects of depth distribution of dispersing larvae on the efficiency of the Marine Protected Areas in the Baltic Sea are examined. Further, the diversity in dispersal and connectivity depending on vertical behaviour is modelled for regions with different tidal regimes in the North Sea, the Skagerrak and the Kattegat. The spatial scales dealt with in the studies varied from global to a highly resolved 182-metres grid. The model results, excepting those from the global study, are based on or compared with in situ-data. / <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At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 2: Submitted.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. 4: Manuscript.</p>

Predators can have large effects on prey populations and on the structure and function of communities. In addition to direct consumption of prey, predators often cause prey to alter their foraging behavior, habitat selection, and morphology. These non-lethal effects of predators can propagate to multiple trophic levels and often exert equal or larger effects upon communities than those of direct consumption. For non-lethal predatory effects to occur, prey must detect and respond to predation risk. While the importance of information transfer in this process has been realized, few studies explore how prey responses are influenced by predator characteristics and environmental conditions that influence the transmission of cues indicative of predation risk. In this dissertation I investigate factors that influence how a single prey species evaluates and responds to predation risk. Here, I examined: 1) the type and nature of cues prey use to evaluate predator risk; 2) how predator identity, predator diet, and the relative risk of predators influence prey response to predation risk; 3) how hydrodynamic conditions influence the delivery of predator cues; 4) how biogeographic trends in predator distribution influence prey response to predation risk; and 5) how genetic structure might vary according to prey geographic location and habitat. To address these questions, I used a common intertidal model system consisting of the rocky intertidal whelk Nucella lapillus (Linnaeus, 1758) and a suite of its predators, the native rock crab Cancer irroratus (Say, 1817), Jonah crab Cancer borealis (Stimpson, 1859), and the invasive green crab Carcinus maenas (Linnaeus, 1758). Nucella use chemical cues emanating from their most common predator (Carcinus maenas) and crushed conspecifics to evaluate predation risk. Nucella from different habitats experience different levels of predation risk, and Nucella from habitats with high levels of predation had larger antipredatory responses to predator risk cues than Nucella that experienced less predation. These chemical cues indicative of predation risk are influenced by hydrodynamic conditions, and Nucella have the strongest anti-predatory response in flow velocities of u= ~4- 8 cm s^-1. Furthermore, Nucella from geographic regions where green crabs are historically absent did not elicit anti-predatory responses, while Nucella from regions where green crabs are common frequently responded. Findings from my dissertation research demonstrate that prey detection and response to predation risk is highly dependent upon predator identity, predator diet, environmental forces, and biogeographic patterns in predator and prey distributions.