The Hidden Cost of Globalization in the Underwater World: Evidence from California's Kelp Forests

Fabien Candau () and Florian Lafferrere
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Fabien Candau: TREE - Transitions Energétiques et Environnementales - UPPA - Université de Pau et des Pays de l'Adour - CNRS - Centre National de la Recherche Scientifique
Florian Lafferrere: TREE - Transitions Energétiques et Environnementales - UPPA - Université de Pau et des Pays de l'Adour - CNRS - Centre National de la Recherche Scientifique

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Abstract: This article examines how maritime regulation affects one of the most important aquatic ecosystems along the California coast: kelp forests. Combining satellite measures of kelp canopy and biomass with AIS vessel trajectories, we exploit variation in pre-policy shipping exposure across kelp cells. After California's Ocean-Going Vessel Fuel Rule ( 2009), kelp improves disproportionately where maritime traffic was highest, with estimated gains of approximately 15-17% per unit of log shipping exposure. Event studies show no differential pre-trends, with the treatment effect appearing sharply at implementation. We apply the same design to the 2011 boundary modification around the Channel Islands, which re-concentrated vessel traffic in specific corridors. Kelp declined most in the cells that had the highest pre-modification shipping exposure.

Keywords: Shipping; California; International trade; Ecosystem services; Difference-in-differences; Vessel traffic; emission control areas; maritime regulation; Kelp forests (search for similar items in EconPapers)
Date: 2026-06-12
Note: View the original document on HAL open archive server: https://hal.science/hal-05655884v1
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