Miocene to Pleistocene transatlantic dispersal of Ceratoconcha coral-dwelling barnacles and North Atlantic island biogeography

Abstract

Coral-dwelling pyrgomatid barnacles (subfamily Ceratoconchinae) were widely dispersed throughout the Paratethys and Mediterranean seas as well as the Atlantic Ocean during the Neogene, but today are limited to the Western Atlantic. Herein, the paleobiogeographic origin and dispersal of the genus Ceratoconcha is studied based on a combination of field, taxonomic, and literature studies. The first confirmed appearances of Ceratoconcha occur in lower Miocene strata (Burdigalian) with two closely related species on both sides of the Atlantic in western France and Florida. Fossils from the Miocene of Lanzarote in the Canary Islands and Pleistocene of Maio in the Cape Verde islands extend the known geographical and temporal range of the Ceratoconcha barnacles in the eastern Atlantic. During the Neogene, dispersal of marine taxa was a two-way process due to tectonic changes both influencing oceanic circulation and appearance and disappearance of oceanic islands. During the early Miocene, gyre formation was weak and the Atlantic Ocean mid-latitudes were warmer than today. This resulted in increased hurricane activity and the expansion of hermatypic coral hosts farther north in the North Atlantic. Normal ocean circulation transported barnacle larvae from east to west, but currents generated by hurricanes may have transported them in the opposite direction towards the margins of the northeastern Atlantic. Islands in between abetted barnacle contact and dispersal. The temporal range for Ceratoconcha is extended considerably in the eastern Atlantic from the early Pliocene to the Pleistocene. The hermatypic host corals of Ceratoconcha suffered a severe decline in the eastern Atlantic and the Mediterranean after the Miocene. Corals were present during the Pliocene and Pleistocene in the Cape Verde Islands. This suggests that the southernmost oceanic islands acted as a tropical refuge for host corals and their likely barnacle symbionts.