Sea Snake Research Articles

Venomics of the beaked sea snake, Hydrophis schistosus: A minimalist toxin arsenal and its cross-neutralization by heterologous antivenoms

The venom proteome of Hydrophis schistosus (syn: Enhydrina schistosa) captured in Malaysian waters was investigated using reverse-phase HPLC, SDS-PAGE and high-resolution liquid chromatography-tandem mass spectrometry. The findings revealed a minimalist profile with only 18 venom proteins. These proteins belong to 5 toxin families: three-finger toxin (3FTx), phospholipase A2 (PLA2), cysteine-rich secretory protein (CRISP), snake venom metalloprotease (SVMP) and l-amino acid oxidase (LAAO). The 3FTxs (3 short neurotoxins and 4 long neurotoxins) constitute 70.5% of total venom protein, 55.8% being short neurotoxins and 14.7% long neurotoxins. The PLA2 family consists of four basic (21.4%) and three acidic (6.1%) isoforms. The minor proteins include one CRISP (1.3%), two SVMPs (0.5%) and one LAAO (0.2%). This is the first report of the presence of long neurotoxins, CRISP and LAAO in H. schistosus venom. The neurotoxins and the basic PLA2 are highly lethal in mice with an intravenous median lethal dose of <0.2μg/g. Cross-neutralization by heterologous elapid antivenoms (Naja kaouthia monovalent antivenom and Neuro polyvalent antivenom) was moderate against the long neurotoxin and basic PLA2, but weak against the short neurotoxin, indicating that the latter is the limiting factor to be overcome for improving the antivenom cross-neutralization efficacy.

On the Abundance of a Pelagic Sea Snake

Abstract We quantified the abundance of pelagic sea snakes, Hydrophis (= Pelamis) platurus, while following slicks that formed drift lines during 3 yr of research in the Golfo de Papagayo, Costa Rica. The number of snakes we observed floating on slicks varied greatly and ranged from 0 to 1,029 per hour. The largest number we observed was highly unusual in recent experience but comparable to earlier reports of sea snake aggregations in the historical literature. Snakes were more abundant on slicks with flotsam during early morning hours on clear, calm days. However, ‘decisions' of sea snakes to spend time floating on slicks are also influenced by other factors that are not known or are poorly understood. Neither temperature nor salinity influenced the number of snakes we observed within the range of the parameters we encountered. We observed only a single snake during 13 days of searching during which there were red tide conditions with cold and turbid water disturbed almost daily by high winds. We also co...

In vitro antibacterial activity of venom protein isolated from sea snake Enhydrina schistosa against drug- resistant human pathogenic bacterial strains

In vitro antibacterial activity of venom protein isolated from sea snake Enhydrina schistosa against drug- resistant human pathogenic bacterial strains

Biological and Biochemical Potential of Sea Snake Venom and Characterization of Phospholipase A2 and Anticoagulation Activity.

This study is designed to isolate and purify a novel anti-clotting protein component from the venom of Enhydrina schistosa, and explore its biochemical and biological activities. The active protein was purified from the venom of E. schistosa by ion-exchange chromatography using DEAE-cellulose. The venom protein was tested by various parameters such as, proteolytic, haemolytic, phospholipase and anti-coagulant activities. 80% purity was obtained in the final stage of purification and the purity level of venom was revealed as a single protein band of about 44kDa in SDS-polyacrylamide electrophoresis under reducing conditions. The results showed that the Potent hemolytic activity was observed against cow, goat, chicken and human (A, B and O positive) erythrocytes. Furthermore, the clotting assays showed that the venom of E. schistosa significantly prolonged in activated partial thromboplastin time, thrombin time, and prothrombin time. Venomous enzymes which hydrolyzed casein and gelatin substrate were found in this venom protein. Gelatinolytic activity was optimal at pH 5-9 and (1)H NMR analysis of purified venom was the base line information for the structural determination. These results suggested that the E. schistosa venom holds good promise for the development of novel lead compounds for pharmacological applications in near future.

Haematological and biochemical reference intervals for three species of hydrophiine sea snakes (Hydrophis curtus, H. elegans and H. peronii) in Australia

This study presents the first set of comprehensive reference intervals (RIs) for plasma biochemistry and haematology for three species of sea snakes common to the Indo-Pacific waters of Australia. In total 98 snakes, composed of Hydrophis curtus (n = 60), H. elegans (n = 27) and H. peronii (n = 11), were captured, clinically examined and had venous blood samples collected.All snakes were deemed healthy and in good to excellent body condition with snout to vent lengths of 40.7–73.9 cm (H. curtus), 68.9–131.4 cm (H. elegans) and 55.0–83.0 cm (H. peronii), respectively. Lymphocyte numbers, alkaline phosphatase, alanine aminotransferase, creatine kinase and lactate dehydrogenase levels were species-dependent. All other parameters are presented as a single range for the three species. Gender ratio was evenly distributed for H. curtus and H. elegans, but 8/11 (73%) of H. peronii were males. No significant differences were detected between males and females for any of the measured blood parameters. Lymph contamination was considered and accounted for. Although only three species of sea snakes are represented in this study, the RIs generated may be useful in the clinical assessment of other sea snake species.

Dehydration and drinking behavior in true sea snakes (Elapidae: Hydrophiinae: Hydrophiini)

AbstractWater is an essential resource affecting behavior and the acquisition of energy, especially in environments where water is spatially or temporally restricted or unavailable. Recent investigations have shown that several species of marine snakes dehydrate at sea and are dependent on environmental sources of fresh water to maintain water balance. However, in this context, little is known concerning the majority of ‘true’ sea snakes (Hydrophiini). We investigated the dehydration and drinking responses of five species of hydrophiin sea snakes collected during the dry season in northern Australia. None of these snakes drank sea water, even when dehydrated. Dehydrated individuals of Hydrophis curtus, H. elegans and H. zweifeli drank fresh water, and the mean threshold levels of dehydration that first elicited drinking were deficits of −26, −29 and −27% of body mass, respectively. Individuals of Aipysurus mosaicus and H. peronii did not drink fresh water when similarly dehydrated. Few snakes that we collected following &gt;4 months of drought drank fresh water immediately after capture. Hydrophiin species appear to have a high resistance to dehydration, which they evidently tolerate in marine habitats for extended periods during drought. Thirst in these species is significantly less sensitive than in other species, suggesting that marine snakes have variable requirements for drinking fresh water. These data illustrate that sea snakes are characterized by diverse responses to dehydration and likely have different osmoregulatory strategies for survival, with implications for better understanding the evolutionary success of secondarily marine vertebrates and their potential responses to future changes in tropical precipitation.

Spatial variation in age structure among colonies of a marine snake: the influence of ectothermy.

Several tetrapod lineages that have evolved to exploit marine environments (e.g. seals, seabirds, sea kraits) continue to rely upon land for reproduction and, thus, form dense colonies on suitable islands. In birds and mammals (endotherms), the offspring cannot survive without their parents. Terrestrial colonies contain all age classes. In reptiles (ectotherms), this constraint is relaxed, because offspring are independent from birth. Hence, each age class has the potential to select sites with characteristics that favour them. Our studies of sea snakes (sea kraits) in the lagoon of New Caledonia reveal marked spatial heterogeneity in age structure among colonies. Sea krait colonies exhibit the endothermic 'seal-seabird' pattern (mixed-age classes within populations) only where the lagoon is narrow. Where the lagoon is wide, most snake colonies are comprised primarily of a single age cohort. Nurseries are located near the coast, adult colonies offshore and mixed colonies in-between. We suggest that ectothermy allows individuals to utilize habitats that are best suited to their own ecological requirements, a flexibility not available to endothermic marine taxa with obligate parental care.

Antivenom cross-neutralization of the venoms of Hydrophis schistosus and Hydrophis curtus, two common sea snakes in Malaysian waters.

Sea snake envenomation is a serious occupational hazard in tropical waters. In Malaysia, the beaked sea snake (Hydrophis schistosus, formerly known as Enhydrina schistosa) and the spine-bellied sea snake (Hydrophis curtus, formerly known as Lapemis curtus or Lapemis hardwickii) are two commonly encountered species. Australian CSL sea snake antivenom is the definitive treatment for sea snake envenomation; it is unfortunately extremely costly locally and is not widely available or adequately stocked in local hospitals. This study investigated the cross-neutralizing potential of three regionally produced anti-cobra antivenoms against the venoms of Malaysian H. schistosus and H. curtus. All three antivenoms conferred paraspecific protection from sea snake venom lethality in mice, with potency increasing in the following order: Taiwan bivalent antivenom < Thai monocled cobra monovalent antivenom < Thai neuro polyvalent antivenom (NPAV). NPAV demonstrated cross-neutralizing potencies of 0.4 mg/vial for H. schistosus venom and 0.8 mg/vial for H. curtus, which translates to a dose of less than 20 vials of NPAV to neutralize an average amount of sea snake venom per bite (inferred from venom milking). The cross-neutralization activity was supported by ELISA cross-reactivity between NPAV and the venoms of H. schistosus (58.4%) and H. curtus (70.4%). These findings revealed the potential of NPAV as a second-line treatment for sea snake envenomation in the region. Further profiling of the cross-neutralization activity should address the antivenomic basis using purified toxin-based assays.

Molecules and morphology reveal overlooked populations of two presumed extinct Australian sea snakes (Aipysurus: Hydrophiinae).

The critically endangered leaf-scaled (Aipysurus foliosquamaI) and short-nosed (A. apraefrontalis) sea snakes are currently recognised only from Ashmore and Hibernia reefs ~600km off the northwest Australian coast. Steep population declines in both species were documented over 15 years and neither has been sighted on dedicated surveys of Ashmore and Hibernia since 2001. We examine specimens of these species that were collected from coastal northwest Australian habitats up until 2010 (A.foliosquama) and 2012 (A. apraefrontalis) and were either overlooked or treated as vagrants in conservation assessments. Morphological variation and mitochondrial sequence data confirm the assignment of these coastal specimens to A. foliosquama (Barrow Island, and offshore from Port Hedland) and A.apraefrontalis (Exmouth Gulf, and offshore from Roebourne and Broome). Collection dates, and molecular and morphological variation between coastal and offshore specimens, suggest that the coastal specimens are not vagrants as previously suspected, but instead represent separate breeding populations. The newly recognised populations present another chance for leaf-scaled and short-nosed sea snakes, but coastal habitats in northwest Australia are widely threatened by infrastructure developments and sea snakes are presently omitted from environmental impact assessments for industry. Further studies are urgently needed to assess these species’ remaining distributions, population structure, and extent of occurrence in protected areas.

Sea Snake Bites Resulted in a Mimic of Brain Death

A 69 year old man with deep coma presented after an alleged history of sea snake bite. Patient presented with irresponsiveness to painful stimuli, complete ptosis, internal and external ophthalmoplegia. He was given continuous ventilator support despite signs of brain stem dysfunction. On admission day 20, the patient was weaned off ventilator and discharged from the hospital. Whenever treating patients who were suspected with a history of snake bite, an emergency physician should always consider severe envenomation in the differential diagnosis of acute neuroparalytic syndrome, which may avert the unfortunate misdiagnoses of brain death.

Polycyclic Aromatic Hydrocarbons (PAHs) and n-Alkanes in Beaked Sea Snake Enhydrina schistose (Daudin, 1803) from the Mandovi Estuary, Goa

An ecotoxicological study were conducted to evaluate the concentrations of PAHs and n-alkanes, in gut, liver and kidney tissues of two individuals of Enhydrina schistose (Daudin, 1803), using gas chromatography/mass spectrometry. The concentrations of PAHs (0.10µg/g) and n-alkanes (8.12µg/g) were elevated in the gut, and liver (PAHs 0.05µg/g tissue, n-alkanes 29.16µg/g tissue). In kidney of both specimen-A and B the PAHs (0.01 and 0.1µg/g) and n-alkanes (0.22 and 2.06µg/g) concentration was detected. This was an initial survey (n=2) and the main goal was to know accumulation and distribution of PAHs and n-alkanes in the sea snakes. This study indicates high accumulation of petroleum hydrocarbon in gut, liver and kidney of sea snake. Since, this species also act as pray for sea eagles and some predatory fishes such as tiger shark, there is high possibilities of PAHs being circulated in marine food chain.

Isolation and Characterization of Biologically Active Venom Protein from Sea Snake Enhydrina schistosa

The present study is designed to investigate the isolation and characterization of biological and biochemical active venom protein from sea snake, Enhydrina schistosa. The highest purification peaks in ion-exchange chromatography on DEAE-cellulose column were obtained for fraction numbers 39-49 when eluted with 0.35-0.45 M NaCl. Eighty per cent purity was obtained in the final stage of purification, and a single protein band of about 44 kDa was visualized in SDS-polyacrylamide gel under reducing condition. Purified venom protein expressed as haemolytic, cytotoxicity and proteolytic activities with lethal concentration (LC50 ) at 2.0 μg/mL. Venom protein exhibits enzymatic activity and hydrolyzed casein and gelatin. Gelatinolytic activity was optimal at pH 5-9. In conclusion, the present results suggested that the sea snake venom might be feasible sources for biologically active substances. Thus, this low molecular weight component of the venom protein could be used in potentially serve biological and pharmaceutical aspects.

Rediscovery of the Yellow-bellied Sea Snake, Hydrophis platurus (Linnaeus, 1766) in Máncora, northern Perú

The presence of the Yellow-bellied Sea Snake (Hydrophis platurus) in the Southeast Pacific is rarely reported, with only one confirmed observation from northern Perú made in the early 1950s. We present new information based on a live-stranded specimen recently found in Peruvian waters, having washed ashore at Máncora (04.1255° S, 81.0958° W) in northern Perú on 12 July 2012. This stranding was associated with a Modoki El Niño warm event, since positive sea surface temperature (SST) anomalies up to 2.5°C were registered at this time.

An antemortem guide for the assessment of stranded Australian sea snakes (Hydrophiinae).

Marine snakes of the subfamily Hydrophiinae are obligate ocean dwellers, unlike their amphibious counterparts, the sea kraits (Laticaudinae), and as such they are often referred to as 'true' sea snakes. This specialization means that the presence of a true sea snake on a beach is atypical and likely indicates disease or injury. Traumatic injuries such as eye, jaw, and spinal lesions have been observed in stranded sea snakes and may present as acute injury or progress to chronic debilitation. Diseases, such as neoplasia, leukemia, and parasite overburden, have also been seen in wild sea snakes, and these animals may present similarly. Sick, moribund, or deceased sea snakes are intermittently found washed ashore along Australian beaches, and these specimens may prove valuable as bioindicators of marine health. This review is intended as a guide to the diagnostic investigation of sick or injured sea snakes by suitably qualified people.

Sea snake harvest in the gulf of Thailand.

Conservation of sea snakes is virtually nonexistent in Asia, and its role in human-snake interactions in terms of catch, trade, and snakebites as an occupational hazard is mostly unexplored. We collected data on sea snake landings from the Gulf of Thailand, a hotspot for sea snake harvest by squid fishers operating out of the ports of Song Doc and Khanh Hoi, Ca Mau Province, Vietnam. The data were collected during documentation of the steps of the trading process and through interviewers with participants in the trade. Squid vessels return to ports once per lunar synodic cycle and fishers sell snakes to merchants who sort, package, and ship the snakes to various destinations in Vietnam and China for human consumption and as a source of traditional remedies. Annually, 82 t, roughly equal to 225,500 individuals, of live sea snakes are brought to ports. To our knowledge, this rate of harvest constitutes one of the largest venomous snake and marine reptile harvest activities in the world today. Lapemis curtus and Hydrophis cyanocinctus constituted about 85% of the snake biomass, and Acalyptophis peronii, Aipysurus eydouxii, Hydrophis atriceps, H. belcheri, H. lamberti, and H. ornatus made up the remainder. Our results establish a quantitative baseline for characteristics of catch, trade, and uses of sea snakes. Other key observations include the timing of the trade to the lunar cycle, a decline of sea snakes harvested over the study period (approximately 30% decline in mass over 4 years), and the treatment of sea snake bites with rhinoceros horn. Emerging markets in Southeast Asia drive the harvest of venomous sea snakes in the Gulf of Thailand and sea snake bites present a potentially lethal occupational hazard. We call for implementation of monitoring programs to further address the conservation implications of this large-scale marine reptile exploitation.

Why does the only ‘planktonic tetrapod’ dive? Determinants of diving behaviour in a marine ectotherm

Marine tetrapods represent powerful models for studying how evolutionary transitions shape the life history traits, physiology and behaviour of animals. Whereas adaptations to diving are driven primarily by the need to secure underwater food, diving in the pelagic sea snake, Hydrophis (Pelamis) platurus, seems less foraging-dependent. Indeed, this reptile captures fish while floating at the sea surface. Despite knowledge about its surface ecology, its underwater behaviour remains mostly unknown. Yet, study of this life phase is a key to understanding how and why this snake dives. In this study, we reanalysed published data on its diving behaviour. The pelagic sea snake spends 95% of its time underwater, where it can dive to 50 m and stay for 3.5 h without breathing. Dives are S-shaped, with a long phase of gradual ascent during which the snake is neutrally buoyant. Snake lungs deflate slowly during this phase at a rate that increases with water temperature, and thus metabolism. Dive duration is linked to inferred lung volume at the start of the dive, suggesting aerobic diving. We propose that pelagic sea snakes dive for multiple reasons, but primarily to avoid sea surface turbulence. Underwater, they can reduce metabolism by targeting cooler water layers. By hovering in the water column, they reduce energy expenditure and escape both surface and bottom predators, while more easily locating their own prey from underneath. Some marine turtles occasionally display S-shaped dives, but the role of such dives remains under debate. We suggest the study of sea snakes can help interpret diving behaviour in other lineages of marine reptiles. © 2014 The Association for the Study of Animal Behaviour. Published by Elsevier Ltd. All rights reserved.

Sea snakes in Australian waters (Serpentes: subfamilies Hydrophiinae and Laticaudinae)--a review with an updated identification key.

Sea snakes (Elapidae, subfamilies Hydrophiinae and Laticaudinae) reach high species richness in the South China Sea and in the Australian region; however, most countries in the two regions still lack up-to-date checklists and identification tools for these snakes. We present an updated reviewed checklist and a new complete identification key to sea snakes in Australian waters. The identification key includes 29 species documented and 4 possibly occurring taxa and is based mostly on easy-to-use external characters. We find no evidence for breeding populations of Laticauda in Australian waters, but include the genus on the list of possibly occurring taxa.

New records of sea snakes at mid-shelf shoals of Australia’s North West Shelf

Offshore reefs of the North West Shelf of Australia support the most diverse and abundant sea snake communities in the world. Ashmore Reef (12° 17′S, 123° 02′ E) is the regional centre of diversity hosting 17 species, including two endemics (Rasmussen et al. 2011; Elfes et al. 2013). However, over the last decade the diversity and abundance of sea snakes at Ashmore Reef have declined drastically. In 2010, only two species (Aipysurus laevis, Astrotia stokesii) were observed and at least five species are now presumed locally extinct (Lukoschek et al. 2013). Here we report on a 2013 survey of Ashmore Reef where, despite extensive boatbased searches over nine days and SCUBA-surveys encompassing 12 ha of reef and lagoonal habitat, no sea snakes were encountered. Identifying the causes of sea snake declines at Ashmore Reef is hampered by a lack of distributional data. To address this, we recorded sea snakes at four previously unsurveyed North West Shelf shoals, namely Echuca, Eugene McDermott, Heywood, and Vulcan, which occur approximately 150–200 km SSE of Ashmore (Fig. 1). Three species were observed (Fig. 1): Aipysurus laevis at Heywood, EugeneMcDermott and Vulcan (one individual at each); Emydocephalus annulatus at Echuca (two individuals) and Heyward (one individual); and the Australasian endemic Aipysurus duboisii at Vulcan (two individuals). These shoals are permanently subtidal (20 m+deep) of consolidated low-relief coral and calcareous algae interspersed with extensive rubble fields. Snakes were seen feeding or resting at 20–25 m or ascending/descending. All three species were also sighted at Hibernia Reef (~30 km NE of Ashmore). Given local extinctions at Ashmore and the demonstrated potential for introgressive hybridisation among Aipysurus spp. in the Timor Sea (Sanders et al. 2014),

Distribution patterns of PAHs in different tissues of annulated sea snake (Hydrophis cyanocinctus) and short sea snake (Lapemis curtus) from the Hara Protected Area on the North Coast of the Persian Gulf, Iran

The levels of 22 polycyclic aromatic hydrocarbons (PAHs) were determined in the skin, liver, kidney and muscle tissues of annulated sea snake (Hydrophis cyanocinctus), and short sea snake (Lapemis curtus) collected from the Hara Protected Area, Persian Gulf during October 2010. Low molecular weight (≤3-rings) had the highest levels in skin, while high molecular weight (≥4-rings) was highest in the kidney. The lowest levels of analyzed PAHs were found in muscle in the both species. H. cyanocinctus (59.37ngg−1 dw) revealed to be significantly more contaminated than L. curtus (50.51ngg−1 dw). Naphtalene was the PAH most frequently detected and at the highest level in the different tissues both species. Di- and tri-cyclic PAHs were predominant in both species suggesting petrogenic origin rather than pyrogenic sources of PAHs. The present study represents the first data of contamination by PAHs in sea snake from the Persian Gulf.

Multilocus phylogeography of the sea snake Hydrophis curtus reveals historical vicariance and cryptic lineage diversity

The Indo‐Australian archipelago (IAA) supports the world's highest diversity of marine fish, invertebrates and reptiles. Many of the marine fish and invertebrates show congruent phylogeographic patterns, supporting a view that the region's complex geo‐climatic history has played an important role in generating its exceptional biodiversity. Here, we examine population genetic structure of the viviparous sea snake, Hydrophis curtus, to assess how past and present barriers to gene flow in the IAA have contributed to genetic and species diversity in a fully marine reptile. Mitochondrial and anonymous nuclear sequences and ten microsatellite loci were used to identify patterns of historical genetic structure and population expansion, reconstruct dated genealogies and assess levels of recent gene flow. These markers revealed strong concordant geographic structure within H. curtus with a prominent genetic break between populations broadly distributed in the Indian Ocean and the West Pacific. These populations were estimated to have diverged in the late Pliocene or early Pleistocene, and microsatellite admixture analyses suggested limited recent gene flow between them despite the current lack of barriers to dispersal, indicating possible cryptic species. Subsequent divergence in the mid–late Pleistocene was detected within the West Pacific clade among the populations in the Phuket‐Thailand region, South‐East Asia and Australia, and two of these populations also showed genetic signals of recent range expansions. Our results show that climatic fluctuations during the Plio‐Pleistocene generated high levels of cryptic genetic diversity in H. curtus, and add to similar findings for diverse other marine groups in the IAA.