October 2021 Vernon Islands

Project Phoenix has just returned from a field trip to the Vernon Islands north of Darwin, Australia.

The Top End is a vastly under-explored area for coral reef research. Indeed, there have been only two papers on the coral fauna published to date despite extensive and flourishing reefs: a checklist of the corals in Darwin Harbour by Jackie Wolstenholme (Wolstenholme et al. 1997) and a paper by Laurie Ferns (Ferns 2016). Conditions in the Top End do make life difficult for coral ecology – huge tides, high turbidity, lots of crocs and stingers – but these hazards are not insurmountable. The massive tidal range means that at certain times of the year it is possible to collect corals without getting wet (Fig. 1).

Fig 1. Acropora cf. millepora exposed at low tide meaning you can collect without getting wet.
Photo credit: Andrew Baird

Thanks to the lowest tides of the year and a trip organized by the The Northern Territory
branch of the Australian Marine Science Association and The Northern Territory Field Naturalists’ Club, Project Phoenix was able to make a lightning visit to sample the corals of the Vernon Islands 40 km north of Darwin. The coral cover was extraordinary, indeed, snorkelers needed a sleeping mat to allow access into the water without getting cut to pieces by the coral. The walls of this blue pool that emerges on these low tides are dominated by vast stands of healthy Acropora spp. and Montipora spp. In contrast, the top of the reef has low coral cover dominated by various merulinids, in particular a number of species of Platygyra. The affinities of the coral fauna are difficult to determine. Many colonies look suspiciously like species on the Great Barrier Reef (Fig. 2), and this is how the fauna has previously been interpreted (Wolstenholme et al 1997) with only one nominal species described from the Top End, Acropora arafura Wallace et al. (2012). However, we suspect the molecules will reveal a much stronger association with the coral fauna of western Australia. Other colonies we collected look like nothing else on earth (Fig. 3), so there are bound to be more endemic species to discover.

Watch this space!

We thank Jim and the staff of Sea Darwin for a wonderful day at sea, Osmar Luiz and family for their superb hospitality and Dion Wedd for the tip-off that the trip was on.

Fig 2. A colony from the Vernon Islands that looks suspiciously like Acropora millepora from the Great Barrier Reef, however the branches are slightly thicker and shorter so we will await molecular analysis to confirm the species identity.
Photo credit: Andrew Baird
Fig 3. An Acropora colony from Darwin Harbour that looks nothing like any of the type material and is almost certainly undescribed.
Photo credit: Andrew Baird

Literature cited

Ferns, L. W. 2016. Coral communities in extreme environmental conditions in the Northern Territory, Australia. Northern Territory Naturalist 27:84-96.

Wallace, C. C., B. J. Done, and P. R. Muir. 2012. Revision and catalogue of worldwide staghorn corals Acropora and Isopora (Scleractinia: Acroporidae) in the Museum of Tropical Queensland. Memoirs of the Queensland Museum 57:1-255.

Wolstenholme, J., Z. D. Dinesen, and P. Alderslade. 1997. Hard corals of the Darwin region, Northern Territory, Australia. Pages 381–398 in R. Hanley, editor. Proceedings of the Sixth International Marine Biological Workshop: The Marine Flora and Fauna of Darwin Harbour, Northern Territory, Australia. Museum and Art Gallery of the Northern Territory and the Australian Marine Sciences Association Darwin.

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