Myrmidon Reef

Author: Andrew Baird

After a 10 hour steam on the Kalinda and a quiet night full of stars; Jupiter, Saturn, Mars and then Venus were all on display, we woke to a glass out in the lagoon on Myrmidon.

[Image: Glass out at Myrmidon Reef]

We were targeting topotypes of a couple of nominal species, in particular Acropora azurea Veron & Wallace 1984. Topotypes are one of the keys to a robust taxonomy. The idea is that the topotype can serve as the molecular archetype of a nominal species against which other specimens can be judged.

Acropora azurae was first described by Veron & Wallace 1984 based on a specimen collected from Myrmidon Reef. Wallace (1999), in her revision of the genus, thought better of this and synonymized the species with A. nana (Studer 1878).

The diving was excellent, the water was crystal clear and the coral was mostly in good shape with the exception of some recent mortality in the shallows, probably as a result of bleaching early in 2020.

[Image: Crystal clear water at Myrmidon Reef]

We are fairly confident that the specimen imaged below is A. azurae (specimen no. 74-2488). We collected this specimen on our 3 or 4th dive at 2 m on the reef crest on the windward side of the reef. The skeleton certainly looks very close to the holotype (Fig. 1). The fact that we have collect at the very same location as the holotype gives us added confidence that it is the same beast.

[Image: Acropora azurae topotype specimen no. 74-2488]

The holotype of A. nana, which is housed in the Museum fur Naturekunde in Berlin, is not in great shape but the image of this specimen that I took on a trip to Europe in 2019, along with the translation of Studer’s (1878) original description, suggests to me that Wallace’s decision to synonymise A. azurea with A. nana was incorrect.

For a start, the branches in A. azurea are much longer that in A. nana (up to 8 cm vs maximum of 2 cm; Fig. 1 a vs b). The radial corallites are tubular with nariform openings and strongly appressed in A. azurae vs tubular with oblique openings and almost at right angles to the branch in A. nana (Fig. 1 c vs d). Finally, the coenosteum of A. azurae consists of fine spinules giving it a frosted appearance vs a strongly costate coenosteum in A. nana (Figure 1 e vs f).

[Figure 1. Acropora azurae vs A. nana]

Unfortunately, we did not find anything that looked like A. nana on our collecting trip to Fiji in May 2018, the type location for A. nana, so we cant compare the molecules just yet. Nonetheless, it is it pretty clear to me that this synonym is incorrect and that A. azurae is a good species.

Otherwise, the food was excellent, the crew were amazing but we didn’t see the green flash.

Literature cited

Studer T (1878) Zweite Abtheilung der Anthozoa Polyactinia, welche wahrend der Reise SMS Corvette Gazelle um die Erde gesammelt wurden. Monatsbericht der Königlich Preussischen Akademie der Wissenschaften zu Berlin 1878:525-550

Veron JEN, Wallace CC (1984) Scleractinia of Eastern Australia – Part V. Family Acroporidae. Australian Institute of Marine Science Monograph Series 6:1-485

Wallace CC (1999) Staghorn corals of the world. CSIRO, Collingwood

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