Manus Island, Papua New Guinea, inundated with pumice following eruption of Titan Ridge submarine volcano.

A series of eruptions from the Titan Ridge submarine volcano, beneath the Bismarck Sea in the southwest Pacific Ocean, has produced a large volume of pumice (a light volcanic rock, produced by the rapid cooling of gas rich lava from submarine eruptions, which can float on the sea), much of which has washed up onto the shores of Manus Island, the largest of the Admiralty Islands and a province of Papua New Guinea. This has caused serious problems for the local population, as it has formed a barrier between them and the sea, too dense to push a boat through, but too quicksand-like to walk across. This in turn has prevented them from harvesting fish and other seafood, the main staples of the island, as well as forcing them to become entirely dependent on the islands limited supply of freshwater for washing and hygiene, rather than bathing in the sea. The large accumulations of pumice are also likely to have smothered local coral reef ecosystems, harming longer-term fishing prospects in the region.

Residents of Manus Island on a beach covered by pumice. ABC.

Pumice forms when hot lava from submarine volcanic eruptions encounters seawater and cools rapidly, simultaneously crystalising and degassing to form a lightweight volcanic rock with many gas filled vesicles (bubbles) within it, which often floats on the sea surface. Big submarine eruptions can produce large volumes of pumice, forming rafts of pumice that cover hundreds of square kilometres, and drift on the ocean surface for months before dissipating or washing ashore. 

Titan Ridge, also known as the Central Bismarck Sea Volcano, is located about 125 km to the southeast of Manus, on the northern edge of the South Bismarck Plate. It is located on the boundary between the Willaumez Transform Fault and an unnamed section of area of seafloor spreading, where the South Bismarck and Pacific plates are being pulled apart, while at the same time the Pacific Plate is moving to the west and the South Bismarck Plate to the east. Here fresh material from the upper mantle is rising up through the fault and being erupted from the volcano as volcanic material, primarily pumice caused by the rapid cooling of a liquid melt containing dissolved gasses. 

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Gehyra rohan: A new species of Gecko from the Bismarck Arichipelago..

The Bismark Archipelago is a large group volcanic islands to the east of Papua New Guinea. This wide scatting of mostly small oceanic islands is a biodiversity hotspot, with each island typically having its own flora and fauna descended from small numbers of individuals that managed to reach the islands after they rose from the sea. Despite this importance, the remote nature of the islands means that many are relatively unexplored by biologists, and the discovery of even quite large animals there is not unusual.

In a paper published in the journal Zootaxa on 14 December 2016, Paul Oliver of the Division of Evolution, Ecology and Genetics, Research School of Biology, and Centre for Biodiversity Analysis at The Australian National University, Jonathan Clegg of Aquatic and Terrestrial Ecology at the Royal Belgian Institute of Natural Sciences and the Biodiversity Inventory for Conservation, Robert Fisher of the Western Ecological Research Center of the U.S. Geological Survey, Stephen Richards of the South Australian Museum and Peter Taylor and Merlijn Jocque, also of Aquatic and Terrestrial Ecology at the Royal Belgian Institute of Natural Sciences and the Biodiversity Inventory for Conservation describe a new species of Gecko from the Bismarck Archipelago.

The new species is placed in the genus Gehyra, which has previously been recorded from Southeast Asia east to the Ryukyu Islands and southeast to the islands of Melanesia and Oceania, and given the specific name rohan, which is the local name in the Nali language given to the species on Manus Island in the Admiralty Islands, a name requested by the people of Sohoniliu Village on Manus Island. The species is exceptionally large, reaching 130-150 mm in length, and brown in colour and mottled with patches of lighter brown, white, black and orange.

Specimen of Gehyra rohan from Mussau Island in the St Matthias Islands. S. Venter in Oliver et al. (2016).

The species was found at a number of separate localities on Manus Island in the Admiralty Islands, as well as possibly on the neighbouring islands of Los Negros and Nauna. It was also found on Mussau Island in the St Matthias Islands, and possibly Fiji. The species was found in both primary and disturbed lowland rainforest, living primarily in the trees, though the species was also found in and around Human habitations and in one case in a cave. One specimen was observed to 'glide' about 3 m to another tree when disturbed.

A molecular phylogenetic study suggests that Gehyra rohan is most closely related to Gehyra georgepottshaasti, a species found on Vanuatu, and Gehyra vorax, a species found in Fiji, but that it probably diverged from these species during the late Miocene; earlier than some estimates for the emergence of the Admiralty Islands, Fiji or Vanuatu. This suggests that the genus Gehyra has been in the region since at least the Miocene, possibly occupying a series of now vanished volcanic islands prior to the emergence of the modern islands.

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