From potential to realized: combining hydrodynamical modelling and habitat quality mapping to study coral connectivity in the Great Barrier Reef

Deffense, Nicolas [UCL] Saint-Amand, Antoine [UCL] Hanert, Emmanuel [UCL]

Over the past few years, our team has been committed to simulate connectivity between the >3000 reefs composing the Great Barrier Reef (GBR). This is achieved thanks to SLIM, a high- resolution unstructured-mesh hydrodynamic model. The simulated water currents are used with a Lagrangian particle tracker to simulate the connectivity between all the reefs composing the GBR. This method has been used for a few years now, but is based on fairly strong assumptions. More particularly, until now we considered that every reef is acting the same way when it comes to larval release and likelihood of settlement. The connectivity resulting from this sequence is thus only a potential connectivity. In order to address this simplification, this study is a first attempt to combine previous SLIM results with a new habitat quality index that includes water temperature, cyclones exposure, Crown-of-Thorns starfish outbreaks and land-based pollutants. The relative weight of those four components is estimated from coral cover measures at different years. By doing so, we obtain a global habitat quality index for each reef of the GBR. Potential connectivity provided by the Lagrangian particle tracker is finally weighted by the habitat quality index to compute a more realistic connectivity network that better describes realized connectivity.