Ecological spillover from a marine protected area replenishes an over‐exploited population across an island chain

Quantifying successful ecological spillover from marine protected areas (MPAs) is challenging yet crucial for conservation planning. The queen conch (Lobatus gigas) supports an iconic Bahamian fishery, but populations are declining. Here we provide evidence for MPAs as a solution: showing that a well‐enforced MPA supplies ecological spillover through larval supply. Dive surveys throughout the Exuma Cays, including a centrally‐located MPA, provided information on abundance, size, and age. Data showed higher‐adult abundance within the MPA and positive associations between enforcement and conch size and age. A biophysical model estimated that MPA larvae settled in unprotected areas, and that MPA larval sources included unprotected sites with densities too low for reproduction. The MPA is currently sustaining nearby populations, yet its future is in jeopardy without upstream larval sources. Our results and consultations with stakeholders regarding management of the Bahamian conch fishery support creating a network of MPAs that exchange larvae for a sustainable future.