Modeling canopy-forming vs. turfing algae competition via a space-implicit model with border dynamics

This study presents a three-species, space-implicit model describing competition between canopy-forming algae Cystoseira s.l. and turf-forming assemblages on rocky coasts, both grazed by sea urchins. The model introduces a key innovation by incorporating community border effects, recognizing that only edge individuals of Cystoseira forests contribute to recruitment, competition, and grazing—an approach analogous to herd behavior in animal ecology. By reproducing transitions among alternative ecological states—coexistence, turf dominance, and barren conditions—the model enhances understanding of the mechanisms driving ecosystem degradation and recovery. These dynamics offer a theoretical basis for environmental and natural resource policy, highlighting how ecological thresholds and feedbacks shape the sustainability of coastal systems. The framework thus supports ecosystem-based management, efficient allocation of conservation resources, and evidence-based policy design aimed at preserving biodiversity, ecological resilience, and the long-term productivity of marine natural capital.