Modelling marine connectivity in the Great Barrier Reef

Details

Supervisors

Hanert, Emmanuel ; Deleersnijder, Eric

Faculty

Ecole polytechnique de Louvain

Degree label

Master [120] : ingénieur civil mécanicien

Abstract

The aim of this thesis is to study the variability of the connectivity in the Great Barrier Reef (GBR) between 2008, 2010 and 2012. In order to do that, the study presents an effort to model the dispersal of coral larvae, of the species Acropora millepora, for the whole GBR in each of the three years considered. Firstly, a high resolution ocean model is devised to build such a model. The hydrodynamic model used is a 2D version of SLIM, an unstructured mesh ocean model. This allows to increase the model’s resolution close to reefs where small scale flow features are important and decrease the resolution in deeper areas where flow features are thought to be more uniform. Validation of the model shows a good agreement with real observations in the south of the GBR while the currents in the north of the GBR would still need improvements to replicate the real hydrodynamics of the region. Secondly, a Lagrangian particle tracker is used to simulate the transport of particles over the currents generated by the ocean model. It generates a connectivity matrix giving for each reef the number of larvae settled onto it and their origin. To interpret all data encapsulated in the connectivity matrix, some connectivity measures are described. Moreover, some protection and restoration measures are defined based on previous connectivity measures and two clustering methods are used. This gives a picture of the connectivity patterns linking the different reefs in the GBR. This information is useful from a management and conservation perspective because this determines which reefs play a major role in the conservation of the GBR. The analysis is made for the three spawning seasons. Finally, in order to have a broader overview of the connectivity in the GBR and to get more relevant and reliable results, data of the three years considered are gathered by using statistics such as the mean and the coefficient of variation. The conclusions drawn from this statistical study show that the reefs that would need more protection are located in the southern part of the center of the GBR and in the northern part of the south of the GBR. The reefs that would be more suitable for restoration practices are located downstream of reefs that would need protection. They are thus located in the south of the GBR. The level of connectivity in the north of the GBR is lower but this region is characterised by high local retention. These final results could be used to inform marine management strategies for achieving restoration and protection of the GBR. These marine management strategies could consist of the placement of Marine Protected Areas (MPAs).