Tuesday, December 22, 2015

New range and habitat records for threatened Australian sea snakes

The rare short nosed sea snake discovered 
on Ningaloo reef, Western Australia. Photo 
Credit: Grant Griffin, W.A. Dept. Parks and 
Scientists from James Cook University have discovered two critically endangered species of sea snakes, previously thought to be extinct, off the coast of Western Australia.

It's the first time the snakes have been spotted alive and healthy since disappearing from their only known habitat on Ashmore Reef in the Timor Sea more than fifteen years ago.

"This discovery is really exciting, we get another chance to protect these two endemic Western Australian sea snake species," says study lead author Blanche D'Anastasi from the ARC Centre of Excellence for Coral Reef Studies at JCU.

"But in order to succeed in protecting them, we will need to monitor populations as well as undertake research into understanding their biology and the threats they face."

The discovery of the critically endangered short nose sea snake was confirmed after a Western Australia Parks and Wildlife Officer, Grant Griffin, sent a photo of a pair of snakes taken on Ningaloo Reef to Ms D'Anastasi for identification.

"We were blown away, these potentially extinct snakes were there in plain sight, living on one of Australia's natural icons, Ningaloo Reef," says Ms D'Anastasi.

"What is even more exciting is that they were courting, suggesting that they are members of a breeding population."

The researchers also made another unexpected discovery, uncovering a significant population of the rare leaf scaled sea snake in the lush seagrass beds of Shark Bay.

The discovery was made 1700 kilometres south of the snakes only known habitat on Ashmore Reef.

"We had thought that this species of sea snake was only found on tropical coral reefs. Finding them in seagrass beds at Shark Bay was a real surprise," says Ms D'Anastasi.

Both leaf scaled and short nosed sea snakes are listed as Critically Endangered under Australia's threatened species legislation, which means they have special protection.

Despite the good news of the find, sea snake numbers have been declining in several marine parks, and scientists are at a loss to explain why.

"Many of the snakes in this study were collected from prawn trawl by-catch surveys, indicating that these species are vulnerable to trawling," says Dr Vimoksalehi Lukoschek from the Centre of Excellence for Coral Reef Studies.

"But the disappearance of sea snakes from Ashmore Reef, could not be attributed to trawling and remains unexplained.

"Clearly we need to identify the key threats to their survival in order to implement effective conservation strategies if we are going to protect these newly discovered coastal populations," Dr Lukoschek says.

B.R. D'Anastasi, L. van Herwerden, J.A. Hobbs, C.A. Simpfendorfer, V. Lukoschek. New range and habitat records for threatened Australian sea snakes raise challenges for conservation. Biological Conservation, 2016; 194: 66 DOI: 10.1016/j.biocon.2015.11.032

Tuesday, December 8, 2015

Sea snake diversity in the Indo-Australian Archipelago

The Indo-Australian Archipelago is a marine biodiversity hotspot centred in Southeast Asia that contains many of the extant viviparous sea snakes. Points of origin of for snake radiations are of interest  in understanding the distribution of current diversity. In an early on-line view of a new paper in the Journal of Biogeography, Ukuwela and colleagues (2015) note that previouis studies found the ancestral area for viviparous sea snakes was Australasian about 6.9 million years ago. The Aipysurus group also originated and speciated in Australasia. However, of the Aipysurus group species, only the specialist fish egg-eaters (Emydocephalus ijimae, E. szczerbaki and A. eydouxii) have colonized Southeast Asia and none have expanded into the Indian Ocean beyond the coast of Western Australia. A Beast analyses recovered a Southeast Asian origin for the core Hydrophis group, and all three methods used indicated that subsequent diversification in this rapidly speciating clade occurred primarily in Southeast Asia, with subsequent dispersals into the Indian Ocean and re-colonization of Australasia.

Ukuwela et al. (2015) found evidence for 34 divergences between lineages older than 0.5 Ma (candidate speciation events); 22 of these have > 0.7 posterior probabilities of occurring in Southeast Asia, 10 in Australasia, and 2 in the Indian Ocean. This implies most sea snake diversity in South East Asia originated from a period of rapid in situ evolution. While viviparous sea snakes originated in Australasia, Southeast Asia and its Indo-Australian Archipelago appears to be their primary centre of speciation. This is contrary to predictions of the overlap or accumulation models. Taxa are not more likely to disperse into, rather than out of, Southeast Asia and the Indo-Australian Archipelago.

The majority of sea snake diversification, including the rapid core Hydrophis radiation, occurred during major climatic and geological events that drove vicariant population and species divergence in many of the region’s marine groups. Viviparous sea snakes might be particularly influenced by ‘soft’ biogeographical barriers (such as incomplete and thus permeable land bridges) because they give birth to live young and thus lack the dispersing planktonic larval stage that is expected to promote population connectivity in most other marine groups (many fish and invertebrates). Several sea snake species accordingly show strong intraspecific genetic structure corresponding to deep-water and historical land barriers. However, biogeographical patterns and the diversification dynamics of the entire sea snake radiation have not previously been quantitatively investigated.

Ukuwela, Kanishka DB, Michael SY Lee, Arne R. Rasmussen, Anslem Silva, Bryan G. Fry, Parviz Ghezellou, Mohsen Rezaie‐Atagholipour, and Kate L. Sanders. 2015. Evaluating the drivers of Indo‐Pacific biodiversity: speciation and dispersal of sea snakes (Elapidae: Hydrophiinae). Journal of Biogeography (2015).