Millepora platyphylla Hemprich & Ehrenberg, 1834

Boissin, E., Pogoreutz, C., Pey, A., Gravier-Bonnet, N. & Psl, S. Planes, 2019, Millepora platyphylla (Cnidaria, Hydrozoa) range extended back to the Eastern Pacific, thanks to a new record from Clipperton Atoll, Zootaxa 4668 (4), pp. 599-600 : 599

The fire coral

Millepora platyphylla Hemprich & Ehrenberg, 1834

(Cnidaria, Hydrozoa)

has a widespread Indo-Pacific distribution observed from the surface to 40 m ( Razak & Hoeksema 2003). However, its extirpation from the East Pacific (Gulf of Chiriqui, Panama) was documented after the 1982-1983 bleaching event ( Glynn & Weerdt 1991). Here, we report the discovery of 5 colonies of M. platyphylla from the eastern Pacific, specifically at Clipperton Atoll, during the TARA Pacific expedition (www.taraexpeditions.org).

These 5 colonies were found on a reef site off the North shore of the island (10-11/08/2018; GPS coordinates: 10°18.857 North and 109°18.857 West) at depths ranging from 28m to 31 m . No colonies were found on the West coast at similar depths. Similarly, no colony was found in shallower waters all around the island during a total of 12 dives of 90 min each performed with 4 divers on the 4 sides of the island from 2-3m down to a depth of fifteen meters. This suggests that M. platyphylla is likely unable to compete for space with the locally abundant reef-building corals Porites spp. and Pocillopora spp. in shallower parts of the reef. Two colonies of the related species Millepora exaesa Forsskål, 1775 were also encountered at 4m depth. This species had already been reported from Clipperton ( Glynn et al. 1996).

These 5 colonies were not recently settled as their surface was about 1 m 2. Their columnar shape is a common morphology for the species. Similarly, a colony was found in 2015 by another French expedition, on the same North shore, but of small size (~ 20 cm 2). Both observations are complementary as the previous team investigated 13 sites around the island from 0 to 2m depth. This new record extends the currently known distribution range of the species back to the Eastern Pacific, the closest populations being French Polynesia in the Central Pacific. The possible recovery in Panama reefs should also be considered. The marine fauna from Clipperton is suggested to be closely related to the one of French Polynesia (4 000 km away; Glynn et al. 1996). For fire corals, the medusoid and larval stages are short-lived and dispersal is likely occurring through rafting, as observed in many marine invertebrates. For instance, rafting of Millepora on pumice has been documented ( Jokiel 1989). We are sequencing and genotyping>1000 specimens of M. platyphylla collected over its entire Indo-Pacific range, which should help unravel the provenance of these Clipperton colonies.