Artificial Reefs as Climate Refugia: Can Human-Made Habitat Positively Affect Spawning Phenology and Distribution for Groupers and Snappers in a Changing World?

Abstract

Groupers and Snappers serve as important mesopredators in reef environments and support known commercial and recreational fisheries. Spawning individuals in these families are often more thermally sensitive and vulnerable to climate change than non-spawning adults, as the energetic costs of reproduction amplify environmental stressors. Most species form fish spawning aggregations (FSAs), where large groups converge on specific sites to reproduce, however, these aggregations are increasingly threatened by overfishing and climate change. Previous studies have shown that snapper FSAs are more resilient than grouper FSAs to climate change-induced habitat loss, but such work has focused only on natural reefs. Many species also use artificial reefs as habitat and, in some cases, spawning sites. Therefore, artificial reefs have potential to serve as climate refugia from losses of natural FSA sites. This study employed a Non-Parametric Probabilistic Ecological Niche (NPPEN) model to evaluate whether artificial reefs in the Southeast U.S., Gulf, and Caribbean influence spawning habitat projections for four focal species under two climate models (GFDL ESM4.1, IPSL CMA6-LR) and two emissions scenarios (SSP2-4.5, SSP3-7.0). I hypothesized that artificial reef inclusion would mitigate spawning habitat loss, reduce core habitat shifts, and that said habitat shifts would be poleward. While lacking data to make a strong conclusion, I also predicted that snappers would be more resilient to climate change than groupers based on previous research. The results revealed mixed support for these predictions. Artificial reefs did not consistently buffer spawning habitat loss, though one species displayed modest benefits. Goliath Grouper (Epinephelus itajara) diverged from expectations, exhibiting consistent spawning habitat gains (+20 to +40%), with larger increases on natural reefs than artificial reefs. Cubera Snapper (Lutjanus cyanopterus) showed moderate gains under SSP2-4.5 but neutral to negative outcomes under SSP3-7.0, notably, this species was the only one to have a significant difference in IHS change values between artificial reefs and natural reefs, with artificial reefs providing greater gains in IHS for ensemble model outputs and both climate scenarios. Spatial and temporal patterns further distinguished the taxa. Goliath Grouper shifted southeastward by 342–498 km and advanced to a winter spawning peak. Cubera Snapper shifted southeastward (236–303 km) and moved spawning earlier into spring. Across all species, artificial reef inclusion consistently increased displacement of centers of gravity, suggesting that artificial reefs expand spatial flexibility of FSAs even when they do not offset habitat loss. Taken together, these findings highlight the complexity of interactions between spawning behavior, climate exposure, and artificial reef utility. While artificial reefs offer modest buffering capacity, their limited footprint and spatial mismatch with future hotspots mean they cannot fully substitute for natural reefs. However, projections revealed consistent opportunities for new artificial reef placement in under-represented regions such as the southern Caribbean and mid-Atlantic Bight. Strategic deployment of artificial reefs in these areas, guided by predictive models, could enhance future spawning resilience. This study underscores the need for fine-scale ecological modeling, long-term monitoring, and adaptive reef management to optimize artificial reef design and placement under changing ocean conditions.