Acropora rongoi Bridge & Cowman, 2024

Bridge, Tom C. L., Cowman, Peter F., Quaưrini, Andrea M., Bonito, Victor E., Frederic, Harii, Head, Catherine E. I., Hung, Julia Y., Halafihi, Tuikolongahau, Rongo, Teina & Baird, Andrew H., 2024, A tenuis relationship: traditional taxonomy obscures systematics and biogeography of the ‘ Acropora tenuis’ (ºcleractinia: Acroporidae) species complex, Zoological Journal of the Linnean Society 202 (1), pp. 1-24 : 16

Acropora rongoi Bridge & Cowman , n. sp.

Zoobank registration: urn:lsid:zoobank.org:act:B53CE95E-FC7F-4D64-8582-6EFEA44C305F

Holotype: MTQ G78411, collected from 1 m depth in the lagoon at Rutaki , Rarotonga, Cook Islands.

Paratypes: MTQ G78418, collected from 17 m depth on the outer reef slope at Papua , Rarotonga, Cook Islands ; MTQ G80232 collected from 12 m depth on the fore-reef slope at ‘ Ōpūnohu Bay , Mo’orea, French Polynesia ; MTQ G80233, collected from 10 m depth on the fore-reef at ‘ Ōpūnohu Bay , Mo’orea, French Polynesia .

Other material examined: MTQ: Cook Islands: G35728 Rarotonga , G35712 , G55536 Aitutaki ; Niue : G54667 , G54670 , G54671 ; Society Islands : G44034 , G58650 Mo’orea .

Holotype: Irregular hispidose colony ~ 75 cm in diameter ( Fig. 6A). Primary branches ≤ 300 mm long and 10–20 mm in diameter, secondary branches ≤ 100 mm long and 10–15 mm in diameter, and tertiary branches 5–15 mm long and 2–4 mm in diameter. Axial corallites tubular and exsert, outer diameter 1.8–2.2 mm, inner diameter 0.9–1.2 mm. Radial corallites closely positioned but not touching, outer diameter 1.2–1.8 mm, inner diameter 0.7–0.8 mm, haphazardly arranged and ranging in shape from tubular with oblique to dimidiate openings through to labellate with flaring lower lips ( Fig. 6B–D). Both axial and radial corallites often show two prominent directive septa one-half to three-quarters of the radius of the calyx, but otherwise septa are weakly developed ( Fig. 6G, H). The coenosteum is costate ( Fig. 5H).

Molecular phylogeny: The two specimens sequenced of this species from Rarotonga ( Cook Islands) are recovered as a reciprocally monophyletic group in all phylogenetic trees ( Figs 2, 3; Supporting Information, Figs S1, S2). The species is sister to a group containing A. aff. pagoensis and A. tenuissima in ML reconstruction, but appears as a direct sister species to A. aff. pagoensis in the SNAPP species tree.

Remarks: Colonygrowthformisirregularcaespitosetohispidose, with indeterminate growth. The holotype, from the shallow lagoon of Rarotonga, has upright branches ( Fig. 6A), whereas paratypes from higher-energy outer reef slopes show thicker, flatter branches with fewer incipient axial corallites. Radial corallites are densely packed (touching in some specimens but not on the holotype), of mixed sizes and shapes and often flaring, giving the colony a spikey, messy appearance. Colour varies from cream to brown. Specimens of A. rongoi in the collection at MTQ were previously identified as A. striata (Verrill, 1866), Acropora elseyi (Brook, 1892) and Acropora florida (Dana, 1846), attributable to the variability in gross morphology of A. rongoi in different habitats. Verrill’s holotype of A. striata from the Ryukyu Islands has similar radial corallite shape but is clearly distinguished from A. rongoi on the basis of molecular and biogeographical evidence. Furthermore, the interpretation of A. striata as hispidose (Shirai 1980, Veron and Wallace 1984, Wallace 1999) is likely to be incorrect because the holotype lacks tertiary branching (see below for further discussion on A. striata ). Acropora elseyi can have similar gross morphology, but radial corallites are tubular to appressed tubular with thick walls and prominent septa, and the coenosteum is composed of elaborate spinules. Colonies from outer reef slopes can also superficially resemble colonies identified as A. florida when tertiary branches become stunted and resemble the ramiculi of A. florida . However, the colony shape of A. florida (Dana, 1846) is arborescent, not hispidose. Acropora affinis (Brook, 1893), synonymized with A. florida by Veron and Wallace (1984), may be hispidose, but this species is in clade III ( Cowman et al. 2020; Fig. 2).

Distribution: Currently known from the Cook Islands, Niue and the Society Islands, French Polynesia in the South Pacific (Supporting Information, Fig. S6).

Etymology: Named for Dr Teina Rongo in recognition of his contribution to research and conservation of coral reefs and the marine environment in the Cook Islands.