Simulating the transport of broadcast coral larvae among the Southern Islands of Singapore

Abstract

Singapore's coral reefs have experienced significant anthropogenic impacts for at least 4 decades. Ongoing reef restoration efforts, however, may not be sustainable if there is no natural coral recruitment. Knowledge of coral reef connectivity, which can be identified using hydrodynamic-advection and individual-based models, can help inform reef management decisions. Here, a 2-dimensional, hydrodynamic, flexible mesh model (MIKE 21 FM) coupled with a Lagrangian particle-tracking module was used to simulate larval transport among Singapore's Southern Islands. In each simulation, neutrally buoyant, passive particles representing coral planulae were released into the hydrodynamic conditions present during the coral multi-species synchronous spawning event of April 2007. When the number of larvae released was proportional to live coral cover (between 2400 and 46 200 particles), 3 islands: Pulau Sudong, Pulau Pawai and Pulau Senang, which all lie within a military Live Firing Area, were identified as the most robust sources of larvae seeding the rest of the Southern Islands. However, when equal numbers of larvae (18 000 larvae per site) were released from all sites in an effort to identify nursery areas with the greatest potential to seed other reefs, 2 different and upstream islands, Sisters' Islands and Kusu Island, were found to be better sources of larvae. We suggest all 5 of these sites should be identified for conservation. Additional effort to enhance coral cover, and hence larval export, at Sisters' Islands and Kusu Island may help increase recruitment on downstream reefs. © Inter-Research 2012.