Hydrodynamic Model used for Larval Dispersal Modelling
We used hydrodynamic models to estimate expected larval connectivity inS. umbilicalis . Simulated three-dimensional ocean currents from these models were used to advect passive particles in the Lagrangian larval dispersal model described below. The hydrodynamic model outputs were from the NEMO Atlantic Margin Model (AMM15; Graham et al. 2018), which has a model horizontal resolution of 1.5 km and 51 terrain-following vertical layers. Simulated flow fields are available at hourly intervals (see Graham et al. 2018 for details of evaluation) and the flow fields from June-Sept 2014 were used to encompass the spawning season of S. umbilicalis . Coscia et al. (2020) demonstrated little interannual variability in the patterns of connectivity matrices of larvae advected using AMM15 output (2008-2014), hence, the background connectivity for 2014 was taken as the annual connectivity. This annual background connectivity between the spawning sites (described below) was used for calculating multi-year spread.