Optimising fertilisation kinetics models for broadcast spawning corals in the genus Acropora

Abstract Synchronous spawning is a specialised adaptation to maximise fertilisation success in free spawning sessile invertebrates. Many factors drive and limit reproduction in such benthic invertebrates including localised hydrodynamic forcing, adult density dependence, and fine-scale gamete interactions, all of which are difficult to measure in situ. Therefore, management and restoration of reproductive populations rely in part on adequate modelling of spawning processes at localised scales. This study used experimentally derived coral-specific parameters and optimisation protocols to improve model predictions of fertilisation outcomes for two common Info-Pacific reef-building corals – Acropora cf. kenti and A. cf. digitifera . Three fine scale parameters that are difficult to measure experimentally – fertilisation efficiency ( Fe ), initial egg concentration ( E 0 ), and polyspermy block time ( tb ) – were optimised for each species. For A. cf. kenti the median optimised Fe value was 0.0194, E 0 was 5 eggs mL − 1 , and tb was 0.10 s. For A. cf. digitifera , the median optimised Fe value was 0.0013, E 0 was 5 eggs mL − 1 , and tb was 10.00 s. Kinetics models were most sensitive to changes in Fe values, as well as species-specific metrics like sperm swimming speed and egg size. Results will enable biophysical coral fertilisation models to better predict reproductive success and support management decisions that safeguard natural reef recovery.