The knowledge gap

Climate change models often predict a simple poleward shift for marine life, assuming species can freely reach new suitable areas. For species with naturally low mobility, such as seahorses, this assumption is deeply flawed. We needed to understand how oceanographic connectivity—the ability of ocean currents to carry juveniles or rafting adults—interacts with climate-driven habitat shifts across their range.

The main approach

To address this, we integrated two powerful computational frameworks. First, we used Ensemble Species Distribution Modelling (ESDM) under high- and low-emission scenarios (SSP5 and SSP2) to map where suitable seahorse habitat will be in 2100. Second, we coupled this with a state-of-the-art biophysical model to simulate two realistic dispersal pathways: short pelagic drifting (14 days) and longer passive rafting (100 days).

Technological challenge: how we tackle the study

The core challenge was linking predictive habitat maps with real-world ocean current simulations. We utilized coastalNet, a biophysical model, to calculate multi-generational dispersal estimates. This graph-theoretical approach allowed us to see which newly-suitable northern areas could actually be reached by seahorses originating from current populations, effectively turning an ‘unlimited movement’ prediction into a ‘connectivity-constrained’ reality.

The main finding

The incorporation of dispersal ability radically changed the forecast, revealing greater conservation risk than previously estimated:

Hippocampus guttulatus is projected to experience severe habitat contraction (up to 45% loss under high-emission scenarios), rather than the predicted expansion seen in standard models.
Hippocampus hippocampus still shows limited range expansion (+8% to +12%), but this is significantly less than the 17% expansion predicted by models that ignore dispersal limits.
Both species face severe losses across the southern distribution, particularly in the Mediterranean and North Africa, where the worst-case scenario (SSP5) projected over 80% and 50% loss for H. guttulatus and H. hippocampus, respectively.

Main implications for conservation and management of biodiversity

This research provides essential, grounded data for the UN 2030 Agenda for Sustainable Development, specifically SDG 14 (Life Below Water). The findings necessitate an immediate shift in conservation strategy:

Prioritize climate refugia: We must strengthen protection measures in areas projected to remain stable, such as the North Sea, the Bay of Biscay, and parts of the northern Iberian Atlantic Coast, especially under the lower-emission SSP2 scenario.
Mitigate local stressors: For isolated, vulnerable populations (e.g., in the Mediterranean’s Thau Lagoon), addressing localized threats like pollution, dredging, and destructive fishing is paramount, as they cannot relocate to escape climate change.
Spatial planning: Conservation efforts must now integrate oceanographic connectivity to identify and safeguard corridors necessary for future range shifts, ensuring that new suitable habitats are reachable.