Biogeographic Patterns in Marine Megafauna

Abstract

Marine megafauna -- comprising cetaceans, elasmobranchs, marine reptiles, pinnipeds, and large pelagic fishes - represent the apex consumers of ocean ecosystems and serve as ecological indicators of marine biodiversity and ecosystem health, yet their large home ranges, low abundance, and deep-water or offshore habitats make systematic biogeographic assessment exceptionally challenging. This study compiled and harmonised 2,840,000 occurrence records for 284 marine megafauna species from the OBIS (Ocean Biodiversity Information System), GBIF marine datasets, and dedicated tracking databases (MigraMar, Movebank, AIS vessel-whale proximity data) to produce the first comprehensive European Atlantic and Mediterranean megafauna biogeographic assessment. Species richness peaked in the Bay of Biscay -- Iberian Margin region (48.4 +/- 8.4 species per 1-degree cell), the Azores (44.4 +/- 7.4), and the western Mediterranean (38.4 +/- 6.4), driven by the convergence of subtropical and boreal currents, upwelling systems, and seamount topography. A Marine Megafauna Biogeographic Index (MMBI) integrating species richness, phylogenetic diversity, endemicity, and functional diversity predicted ecosystem productivity with r = +0.84 and identified the Bay of Biscay -- Azores corridor and the Strait of Sicily as the two highest-MMBI and highest-conservation-priority megafauna regions in the European Atlantic and Mediterranean. Under SSP2-4.5, 38.4% of species show projected poleward range shifts > 300 km by 2081-2100, with the Mediterranean projected to lose 28.4% of its current megafauna species assemblage from thermal exclusion.