Return of the Ghosts of Dispersal Past: Historical Spread and Contemporary Gene Flow in the Blue Sea Star Linckia Laevigata

Marine animals inhabiting the Indian and Pacific oceans have some of the most extensive species ranges in the world, sometimes spanning over half the globe. These Indo-Pacific species present a challenge for study with both geographic scope and sampling density as limiting factors. Here, we augment and aggregate phylogeographic sampling of the iconic blue sea star, Linckia laevigata Linnaeus, 1758, and present one of the most geographically comprehensive genetic studies of any Indo-Pacific species to date, sequencing 392 base pairs of mitochondrial COI from 791 individuals from 38 locations spanning over 14,000 km. We first use a permutation based multiple-regression approach to simultaneously evaluate the relative influence of historical and contemporary gene flow together with putative barriers to dispersal. We then use a discrete diffusion model of phylogeography to infer the historical migration and colonization routes most likely used by L. laevigata across the Indo-Pacific. We show that estimates of genetic structure have a stronger correlation to geographic distances than to “oceanographic” distances from a biophysical model of larval dispersal, reminding us that population genetic estimates of gene flow and genetic structure are often shaped by historical processes. While the diffusion model was equivocal about the location of the mitochondrial most recent common ancestor (MRCA), we show that gene flow has generally proceeded in a step-wise manner across the Indian and Pacific oceans. We do not find support for previously described barriers at the Sunda Shelf and within Cenderwasih Bay. Rather, the strongest genetic disjunction is found to the east of Cenderwasih Bay along northern New Guinea. These results underscore the importance of comprehensive range-wide sampling in marine phylogeography

Development of an Integrated System for the Simulation and Assessment of Produced Water Discharges from Offshore Platforms

Techniques for modeling of marine pollution have been studied for decades. Specialized modeling methods have been used to simulate the dispersions of pollutants from offshore outfalls. Produced water, the largest volume waste stream discharged from offshore oil and gas production activities, is a complex mixture of dissolved and particulate organic and inorganic chemicals including metals and hydrocarbons. In recent years, the growing importance and interest in the ocean environment assessment has urged further evaluation of produced water impacts on the marine ecosystem. This thesis study describes an integrated system for the modeling and assessment of produced water discharges in coastal area. The system integrates ocean circulation simulation, pollutant fate and transport modeling that couples near field mechanisms and far field processes, and risk assessment approaches where exposure risks and probabilistic risks are evaluated. A literature survey is first introduced to review and present capabilities and limitations of the most widely used methods and models associated with assessment of the impact of marine pollution. This review identified the need for an integrated system with configurations of numerical schemes of Princeton Ocean Model (POM) for ocean circulation simulation, a Lagrangian method to simulate near field transport processes in three dimensional cross flows, and a numerical solution for far field transport modeling. The physical models are dynamically integrated to ensure mass and energy conservation. Furthermore to assess risks, a modified Monte Carlo method which uses a statistical model to establish the relationship between uncertainty parameters and output concentrations is integrated with physical modeling system along with risk characterization approaches to map risk levels. Evaluation and field validations are conducted for each individual sub-models and for the overall integrated modeling results. Specifically, the near field model is validated against a field study performed in USA platform located about 100 miles of New Orleans Louisiana. The computational efficiency and accuracy of the far field model are evaluated through test cases in comparison with concentration distribution results generated from an exact analytical solution and a RWPT (Random Walk Particle Tracking) method. Validations of ocean circulation results and the integrated produced water dispersion results are conducted in a case study carried out on the Grand Banks of Newfoundland, Canada. Validations show good performance of the developed modeling system which is used to provide satisfactory 3D simulation of marine pollutant dispersion for effective assessment and management of offshore waste discharges. Finally, a risk assessment is carried out to predict risks associated with predicted lead and benzene concentration resulting from potential future produced water discharges in the East Coast of Canada. This research study provide a tool for the modeling of complex transport processes in the coastal area, and improved methods for risk assessment of produced water impacts on the regional water environment