Diversity of zoantharian species and their symbionts from the Macaronesian and Cape Verde ecoregions demonstrates their widespread distribution in the Atlantic Ocean

Zooxanthellate zoantharians (Cnidaria: Anthozoa) are commonly found in tropical and subtropical marine regions around the world. However, due to the low genetic variability of commonly used DNA markers combined with high levels of intraspecific morphological variation, misidentifications and species synonyms are commonly found in the literature. In this study, zoantharians from the suborder Brachycnemina collected in the Macaronesia and Cape Verde ecoregions were studied combining morphological, molecular and ecological data, in order to comprehensively assess the species diversity of the region. Moreover, molecular analyses of endosymbiotic Symbiodiniaceae zooxanthellae were also performed to provide more information on each holobiont. Our integrative results demonstrate that Brachycnemina species diversity increases as seawater temperature rises toward the tropics with a total of nine species recorded: one from waters around northern Madeira, five in the Canary Islands and seven in the southernmost Cape Verde Archipelago. All species were seen to host either Symbiodiniaceae of the genera Symbiodinium (former Symbiodinium ‘Clade A’) or Cladocopium (former Symbiodinium ‘Clade C’). Moreover, this study records for the first time the presence of Palythoa grandis, P. aff. clavata, P. grandiflora, an unknown Zoanthus species and Z. pulchellus in the East Atlantic Ocean. These results show no endemic zooxanthellate zoantharians in the East Atlantic, with all species shared with the West Atlantic.