A new blue astrangiid coral from the Southwestern Atlantic: coral diversity under globalization

Abstract

Two Astrangia Milne Edwards & Haime, 1848 species have been identified in shallow water environments along the Brazilian coast: A. solitaria (Le Sueur, 1817) and A. rathbuni Vaughan, 1906. Astrangia woodsi Wells, 1955 is an incrusting coral with blue-gray polyps, and a darker skeleton originally described to the Eastern Coast of Australia. This species was for the first time identified out of its natural border in 2021, on a rocky reef in the Arabian Sea. In the last decades, Indo-Pacific dendrophylliids belonging to the genus Tubastraea Lesson 1830 became widespread in the Atlantic. Indeed, two other exotic marine cnidarians have been recently introduced in the Tropical Atlantic, the octocorals Sarcothelia sp. Verrill, 1928 and Briareum hamrum (Gohar, 1948). Here, we describe a new Astrangia species to the Northeastern Brazilian coast. Scanning electron microscopy images of the corallites supported the taxonomic analysis and description of the new astrangiid. Early confounded with the A. woodsi, this new coral may be promptly recognized in biofouling because of its color and solitary development. Indeed, the incorporation of iron salts into the aragonite fibers may result in blue carbonate skeletons – an exquisite condition observed in a small group of reef-building octocorals, the Helioporidae Moseley, 1876. Scleractinians have usually white aragonite skeletons. However, like the helioporids, Astrangia sp. nov. has also a blue skeleton, a natural camouflage that is likely to prevent it to be noticed somewhere else. Finally, a key of the world Astrangia species is provided for the first time.