Uncovering the Fine-Scale Connectivity of Coral Reefs via Lagrangian Coherent Structures.

The resilience of reefs to disturbances largely depends on the effectiveness of reef larvae to restore populations through ocean dispersal. Improving quantitative predictions of reef connectivity has therefore emerged as a priority area of coral reef science. Today, ocean circulation models are increasingly used to drive particle-tracking studies of reef connectivity. While providing useful information, such as the probability of connectivity between individual sites, such approaches typically do not identify the flow structures that control dispersal. Here, we show how novel Lagrangian Coherent Structures (LCS) methods, specifically developed to reveal key and often hidden flow transport structures, can help to visualize and interpret the connectivity patterns within morphologically complex reef systems. As an example case study, we consider transport within Ningaloo Reef in Western Australia. Our results demonstrate that LCS-based approaches not only support existing techniques for assessing connectivity but also, via the creation of LCS-based Synoptic Flow Maps, provide additional deep insight. These results can aid reef conservation management efforts, by providing quantitative justification for the placement of Marine Protected Areas based on the persistent flow structures that often occur within and surrounding reefs.