Saturday, January 5, 2019

[Cnidaria • 2018] Heliopora hiberniana • Integrated Evidence Reveals A New Species in the Ancient Blue Coral Genus Heliopora (Octocorallia)

Heliopora hiberniana 
 Richards, Yasuda, Kikuchi, Foster, Mitsuyuki, Stat, Suyama & Wilson, 2018

Maintaining the accretion potential and three dimensional structure of coral reefs is a priority but reef-building scleractinian corals are highly threatened and retreating. Hence future reefs are predicted to be dominated by non-constructional taxa. Since the Late Triassic however, other non-scleractinian anthozoans such as Heliopora have contributed to tropical and subtropical reef-building. Heliopora is an ancient and highly conserved reef building octocoral genus within the monospecific Family Helioporidae, represented by a single extant species – H. coerulea, Pallas, 1766. Here we show integrated morphological, genomic and reproductive evidence to substantiate the existence of a second species within the genus Heliopora. Importantly, some individuals of the new species herein described as Heliopora hiberniana sp. nov. feature a white skeleton indicating that the most diagnostic and conserved Heliopora character (the blue skeleton) can be displaced. The new species is currently known only from offshore areas in north Western Australia, which is a part of the world where coral bleaching events have severely impacted the scleractinian community over the last two decades. Field observations indicate individuals of both H. coerulea and H. hiberniana sp. nov. were intact after the 2016 Scott Reef thermal stress event, and we discuss the possibility that bleaching resistant non-scleractinian reef builders such as Heliopora could provide new ecological opportunities for the reconfiguration of future reefs by filling empty niches and functional roles left open by the regression of scleractinian corals.


Subclass OCTOCORALLIA Haeckel, 1866
Order HELIOPORACEA Bock, 1938

Family Helioporidae Moseley, 1876
Genus Heliopora de Blainville, 1830

Diagnosis as for Family. Massive skeleton of crystalline aragonite, polyps in cylindrical tubes, interconnected via solenia.

Type species Heliopora coerulea Pallas, 1766.

Heliopora hiberniana sp. nov.

Etymology: Latin, feminine, in reference to the type locality, adjectival form of Hibernia.

Distribution: Hibernia Reef, Ashmore Reef, Scott Reef, Browse Is., NW Australia.

Figure 1: Two sympatric morphs of Heliopora occur in NW Australia.
(A) The slender-branching Heliopora hiberniana sp. nov. (foreground) growing in situ with Heliopora coerulea (background) at the type locality, Hibernia Reef, NW Australia. (B) A broken branch reveals the characteristic blue skeleton of H. coerulea. (C) A broken branch (red circle) reveals the white skeleton of H. hiberniana sp. nov.


Figure 2 Comparative morphology of Heliopora coerulea and Heliopora hiberniana sp. nov.
(A) Close up of H. coerulea showing the blue coloration of the skeleton. (B) Simple elaborations on echinulations in H. coerulea. (C) Close up of H. hiberniana sp. nov. showing the presence of autopores and absence of worm tubes. (D) Highly elaborated echinulations in H. hiberniana sp. nov. (E) Cladistic semi-strict consensus tree (of four equally-parsimonious trees) based on ten morphological characters confirms white and intermediate forms of Heliopora hiberniana sp. nov. are monophyletic and derived within blue Heliopora coerulea.

Diagnosis: Heliopora hiberniana sp. nov. is distinguished from H. coerulea by a slender branching growth form, smaller and more numerous autopores, and highly elaborated echinulations. Some colonies (like the type material) are clearly distinguished by the presence of a white skeleton however this does not appear to be a fixed diagnostic trait as some H. hiberniana sp. nov. individuals retain the blue or intermediate colouration. H. hiberniana sp. nov. is distinguished from H. compressa Verrill, 1864 by its fine branching clump growth form and highly elaborated echinulations. Heliopora compressa is described to have a thick, massive or encrusting base that forms plates with thin edges or lobe-like branches. It also has 2–3 elaborations per echinulation rather than 3–6 as in H. hiberniana sp. nov. Heliopora hiberniana sp. nov. is distinguished by H. fijiensis Hoffmeister, 1945 by its fine branching clump form, smaller autopores (0.58–0.69 mm) and smaller number of pseudosepta (12–15). Heliopora fijiensis is known only from fossil material and it is described as having an encrusting growth form with 14–17 pseudosepta and an autopore diameter of 0.75–0.9 mm. The number of elaboration on echinulations were not recorded.

Remarks: There are only three available names of Heliopora listed in the World Register of Marine Species: H. coerulea (Pallas, 1766), H. fijiensis Hoffmeister, 1945 † and H. compressa Verrill, 1864. All are differentiated from H. hiberniana sp. nov. by morphology. Heliopora fijiensis remains known only from fossil material, and H. compressa is considered a nomen dubium.

The new species was observed growing in close association with Halimeda sp. at the type locality (Fig. 5). Squat lobster Alpheus obesomanus Dana, 1852 (Arthropoda; Crustacea; Malacostracea; Decapoda; Alpheidae) were observed residing in colony tips (Fig. 5F).

Figure 5 Heliopora hiberniana sp. nov. growing in situ at the type locality, Hibernia Reef.
 (A) Branching clump growing in close association with Halimeda sp., (B) Small branching clump. (C) Heliopora hiberniana sp. nov. (top) growing in situ with H. coerulea (bottom) at the type locality. (D) Heliopora hiberniana sp. nov. with a broken branch showing the white skeleton, (E) Side attached open branching colony with encrusting base; (F) Heliopora hiberniana sp. nov. (background) growing in situ with Stylophora pistillata in the foreground.

Zoe T. Richards, Nina Yasuda, Taisei Kikuchi, Taryn Foster, Chika Mitsuyuki, Michael Stat, Yoshihisa Suyama and Nerida G. Wilson. 2018. Integrated Evidence Reveals A New Species in the Ancient Blue Coral Genus Heliopora (Octocorallia). Scientific Reports. 8, 15875.  DOI: 10.1038/s41598-018-32969-z