Global biodiversity and biogeography of coastal octopuses

This chapter provides an updated overview of extant octopus species richness from the aspects of taxonomic rank, lifestyles, and habitat and identifies global hotspots of coastal species richness (at both realm and ecoregion levels) for the ranks of family and genus. Also assessed are global patterns of coastal endemicity and modality types of the latitudinal gradients of species richness. Most octopus species are coastal (47% and 57% of genera and species, respectively), and the best-known shelf-associated species inhabit the realms of the Central Indo-Pacific (CIP; 31%), Temperate Northern Pacific (TNP; 29%), and Temperate Australasia (TAUS; 15%). Yet, at increased spatial resolution (eco-region level), the richness hotspot for coastal octopuses is located outside CIP, in the Central Kuroshio Current eco-region (CKC; with 21 species) located within the TNP. The Caribbean and Cortezian ecoregions are hotspots for Octopus, the most diverse genus. Shelf-associated octopuses show the highest rates of endemism in the Southern Ocean (87%), followed by Temperate South America (67%) and TAUS (65%), and the lowest endemism in the Arctic (17%). On a global scale, the latitudinal gradients of species richness (LGSR) of coastal octopuses peaks at 25°N, rather than near the equator. The existence of bimodality of LGSR in coastal octopuses suggests that species may have evolved through thermal adaptation at the edges of the tropics, but analyses of historical biogeography and species–area–energy hypotheses will be necessary to fully understand broad-scale variation in octopus biodiversity and biogeography.