Biophysical models resolution affects coral connectivity estimates

Abstract

Estimating connectivity between coral reefs is essential to inform reef conservation and restoration. Given the vastness of coral reef ecosystems, connectivity can only be simulated with biophysical models whose spatial resolution is often coarser than the reef scale. Here, we assess the impact of biophysical models resolution on connectivity estimates by comparing the outputs of five different setups of the same model with resolutions ranging from 250 m to 4 km. We show that increasing the model resolution around reefs yields more complex and less directional dispersal patterns. With a fine-resolution model, connectivity graphs have more connections but of weaker strength. The resulting community structure therefore shows larger clusters of well-connected reefs. Virtual larvae also tend to stay longer close to their source reef with a fine-resolution model, leading to an increased local retention and self-recruitment for species with a short pre-competency period. Overall, only about half of the reefs with the largest connectivity indicator values are similar for the finest and coarsest resolution models. Our results suggest that reef management recommendations should only be made at scales coarser than the model resolution. Reef-scale recommendations can hence only be made with models not exceeding about 500 m resolution.

Oceanographic connectivity strongly restricts future range expansions of critical ecosystem structuring species

“…First, the BM integrates ocean current velocity fields at a resolution of 1/16° [Ref], meaning that smaller-scale nearshore processes might be unresolved 44 . These can be important for short-distance dispersal events (e.g., gametes, zygotes, spores), potentially influencing local connectivity patterns 45,46 . Similarly, uncertainty exists for long-distance dispersal events (e.g., rafting), as wind and wave effects on drift velocities were not explicitly considered, but can also be relevant in structuring dispersal pathways 47 .…”

Coral reef potential connectivity in the southwest Indian Ocean

“…We therefore do not resolve connectivity (including vertical connectivity) within reef systems (e.g. Saint-Amand et al, 2023; Takeyasu et al, 2023). In this study, most structure in the coral reef networks emerging from multi-generational larval dispersal is at scales of 100 km or greater.…”

“…Drifter trajectories suggest that a failure to resolve reef-scale oceanographic processes likely overestimates cross-shore transport (and therefore connectivity) between coral islands (Monismith et al, 2018). Reef-scale connectivity simulations have largely been limited to 2D hydrodynamic models investigating dispersal in shallow water (Grimaldi et al, 2022; Saint-Amand et al, 2023), in contrast to the 3D hydrodynamic model used in this study, necessitated by the much larger spatial scale, and larval transport across deep ocean. Nevertheless, these studies suggest that SECoW may overestimate the connectivity of remote reefs, which may have the consequence of increasing the connectivity timescale between reefs (supplementary materials, fig.…”

Coral reef potential connectivity in the southwest Indian Ocean

“…We therefore do not resolve connectivity (including vertical connectivity) within reef systems (e.g. Saint-Amand et al 2023;Takeyasu et al 2023). In this study, most structure in coral reef networks emerging from multi-generational larval dispersal is at scales of 100 km or greater.…”