Efate Research Articles

Possible Gouty Arthritis in Lapita‐Associated Skeletons from Teouma, Efate Island, Central Vanuatu

The discovery of the ca. 3,000‐year‐old Lapita cemetery site of Teouma on Efate Island, Vanuatu, has for the first time provided the opportunity for biological anthropologists to begin to address issues of health at a population level in these previously elusive people. Macroscopic observation and radiography have revealed the occurrence of erosive arthritis in seven individuals from Teouma. Differential diagnosis of the disease causing the lesions includes gout, rheumatoid arthritis, and the seronegative spondyloarthropathies. On the basis of the type and pattern of lesions and the epidemiology of erosive arthropathies in the Pacific Islands, a diagnosis of gout may be tentatively proposed, giving a crude prevalence rate of 35% (n = 7/20) in the sample. The occurrence of gout in a skeletal sample of possible Polynesian ancestors provides tantalizing clues to the antiquity of a disease which is a significant modern health problem in some Pacific Island populations.

Lapita Migrants in the Pacific's Oldest Cemetery: Isotopic Analysis at Teouma, Vanuatu

Teouma, an archaeological site on Efate Island, Vanuatu, features the earliest cemetery yet discovered of the colonizers of Remote Oceania, from the late second millennium B.C. In order to investigate potential migration of seventeen human individuals, we measured isotopes of strontium (87Sr/86Sr), oxygen (δ18O), and carbon (δ13C), as well as barium (Ba) and strontium (Sr) concentrations, in tooth enamel from skeletons excavated in the first two field seasons. The majority of individuals cluster with similar isotope and Ba/Sr ratios, consistent with a diet of marine resources supplemented with plants grown on the local basaltic soils. Four outliers, with distinctive 87Sr/86Sr and δ18O, are probably immigrants, three of which were buried in a distinctive position (supine, with the head to the south) with higher Ba/Sr and δ13C, consistent with a terrestrial, nonlocal diet. Among the probable immigrants was a male buried with the crania of three of the locally raised individuals on his chest.

Basalts from the Efate Island Group, central section of the Vanuatu arc, SW Pacific: geochemistry and petrogenesis

Basalts of the Efate Island Group (<0.7 Ma) occur in the central part of the Vanuatu island arc between the ‘normal’ southern section of the arc and the central part of the arc affected by collision with the Eocene D'Entrecasteaux Ridge. These basalts form small cones constructed upon a volcaniclastic apron principally composed of trachydacitic breccias. Temporal and compositional features allow identification of three basalt groups. Subtle compositional differences exist between two of these suites, whereas the third shows pronounced enrichment in K and Rb, with few differences for other elements. These variations are taken to record slight compositional variations in the ambient mantle wedge composition, with the high-K, high-Rb suite deriving from localised zones relatively enriched in phlogopite. Compared with other Vanuatu arc basalts, the Efate basalts show appreciable enrichment in Sr and P 2O 5. The Pb isotopic characteristics of the Efate basalts are commensurate with the transitional position of this island within the Vanuatu arc, between the southern arc lavas and those erupted in the region affected by D'Entrecasteaux Ridge collision. However, 87Sr/ 86Sr values (0.70387–0.70424) are slightly higher and 143Nd/ 144Nd values slightly lower than predicted by the spatial change of these values along the arc. These features are taken to indicate derivation of the Efate basalts from a local, unusual mantle source. Two contrasting models are considered to account for the unusual features of the source mantle of these basalts. Model 1 suggests that the high Sr and P 2O 5 characteristics of the peridotite source of the Efate basalts were produced by subduction of an intraplate volcano similar to ORSTOM seamount, currently subducting immediately northwest of Efaté. Recent studies have demonstrated massive P 2O 5 and Sr enrichments in highly altered formerly glassy seamount lavas and hyaloclastites. Model 2 proposes that the ambient strongly depleted mantle wedge has been locally modified by carbonatite metasomatism. A well-defined tear or gap in the subducted slab beneath the Efate sector of the Vanuatu arc may have provided appropriate conditions for production of an ephemeral carbonatite partial melt from asthenosphere convecting into the hole in the slab. This melt invaded the mantle wedge, stamping enrichment of Sr and P 2O 5 on a mantle wedge peridotite that had already been metasomatised by fluids derived from sediments on the subducting plate.

Enquête pastorale et enquête ethnographique : une question de symétrie: Conversation avec Philippe Daget

A number of radiocarbon dates, both published and unpublished have been obtained from archaeological deposits across the Teouma site on the island of Efate in Vanuatu. These are on a range of materials from the midden and associated cemetery including charcoal (13) and shell (7) as well as a number of less commonly dated 14C sample types including bone from 2 terrestrial giant tortoises (?Meiolania damelipi), 8 pigs (Sus scrofa) and 2 chickens (Gallus gallus). Thirty-six human bone collagen dates and 5 Conus sp. shell ring artifacts from the cemetery context have been discussed in detail elsewhere (Petchey et al., 2014). In this paper, we evaluate the radiocarbon data according to observed contextual associations and established understandings of 14C offsets, and collate all available information in a Bayesian framework to establish the age and duration of the settlement at Teouma. This analysis provides a maximum age range for the Lapita deposits of between 3000 and 2560 cal BP and a most likely start date of 2920–2870 cal BP and end date of 2870–2750 cal BP (68.2% prob.). This is slightly younger age for the deposits than previously reported, but is in keeping with evaluation of the burials themselves, the majority of which are dated to between 2940 and 2720 cal BP. This age range indicates that the site was in use at the same time as colonization events in Tonga (2850–2830 cal BP) and Fiji (3020–2860 cal BP), and supports the hypothesis that Vanuatu was at the center of a region-wide interaction sphere for several generations after initial settlement.

Sea Kraits (Squamata: Laticauda spp.) as a Useful Bioassay for Assessing Local Diversity of Eels (Muraenidae, Congridae) in the Western Pacific Ocean

Collection of eels of the families Muraenidae and Congridae is often hampered by logistical and procedural difficulties. Sea kraits of the genus Laticauda may be useful bioassays for moray and conger eels in the western Pacific Ocean. Some widely distributed species of Laticauda appear to prey exclusively on eels, and these eels are readily palpated from snakes after they return to land to digest their prey. We removed 79 eels from 276 snakes on the island of Efate, Republic of Vanuatu, during November and December of 2000. Species diversity inferred from these eels was markedly different from the diversity inferred from eels from Vanuatu deposited in the Australian Museum, perhaps reflecting differential abilities of snakes and humans to capture certain eel species. This bioassay technique is inexpensive and logistically simple and may prove complementary to more traditional collecting methods.

Relationships between sexual dimorphism and niche partitioning within a clade of sea-snakes (Laticaudinae)

Previous studies in Fiji have shown that females of the amphibious sea-krait Laticauda colubrina are much larger than males, and have larger heads relative to body size. The dimorphism has been interpreted in terms of adaptation to a sex divergence in prey-size: females primarily eat large (conger) eels rather than smaller (moray) eels. The hypothesis that dimorphism is affected by niche divergence predicts that the degree of sex dimorphism will shift when such a species invades a habitat with a different range of potential prey sizes. On the island of Efate in Vanuatu, L. colubrina and a regionally endemic sibling species (L. frontalis) both consume smaller eels (in absolute terms, and relative to the snake's body size) than do the previously-studied Fijian snakes. Patterns of morphology and sexual dimorphism have shifted also. Both Vanuatu taxa are slender-bodied, and frontalis is smaller and less dimorphic than L. colubrina. Females grow larger than males in all taxa, and have larger heads (relative to body length), but the degree of sexual divergence is lower in Vanuatu (especially in frontalis). Dietary overlap (in prey species as well as size) is high between adult frontalis and juvenile colubrina, but the two taxa differ in prey size/predator size relationships. In particular, male frontalis eat very small prey and have very short heads. Our results are consistent with the hypothesis that sex differences in the mean adult body sizes and relative head sizes of laticaudine snakes are linked to sex differences in feeding biology.

Reproductive isolating mechanisms between two sympatric sibling species of sea snakes.

Mechanisms that maintain species isolation within sympatric congeners have attracted analysis in many kinds of organisms, but not in snakes. We studied two sibling species of amphibious sea snakes (Laticauda colubrina and L. frontalis) on the island of Efate, in the Pacific Ocean republic of Vanuatu. The two taxa are almost identical morphologically, except that L. colubrina grows much larger than L. frontalis. No natural hybrids have been reported, and geographic distributions of the two taxa suggest the possibility of sympatric speciation. Our fieldwork shows that the two taxa are often syntopic and overlap in breeding seasons. Behavioral studies in outdoor arenas show that the separation between these two taxa is maintained by species-specific cues that control male courtship. Males of both species courted conspecific females but not heterospecific females. The proximate mechanism driving this separation involves chemical cues. Adult females of both taxa possess distinctive lipids in the skin. Males directed courtship behavior (chin-pressing) to hexane-extracted samples of lipids from conspecific but not heterospecific females. Males of the dwarf species (L frontalis) were more selective courters than were those of the larger taxon (L. colubrina), perhaps because a preference for courting larger females means that L. colubrina males would be unlikely to court L. frontalis-sized (i.e., small) females even in the absence of pheromonal barriers.

New Extinct Mekosuchine Crocodile from Vanuatu, South Pacific

Abstract We describe a new species of crocodile (Reptilia: Crocodyloidea: Mekosuchinae) from a maxilla recovered at the Arapus archaeological site, on the island of Efate, Vanuatu, South Pacific. As with mekosuchine species in New Caledonia and Fiji, Mekosuchus kalpokasi sp. nov. was a small, possibly terrestrial carnivore that is now extinct. The differences between the Efate specimen and previously described species of Mekosuchus warrant recognition of a new species. Based on its association with Efate's earliest known human inhabitants, dating approximately 3000 cal yr B.P., the extinction of M. kalpokasi and other insular mekosuchines may have been anthropogenic. The lack of adequately dated pre-Quaternary and Quaternary vertebrate fossil records from Vanuatu, New Caledonia, and Fiji (as well as other smaller islands) precludes determining the timing and route of dispersal of mekosuchine crocodyloids.

REPRODUCTIVE ISOLATING MECHANISMS BETWEEN TWO SYMPATRIC SIBLING SPECIES OF SEA SNAKES

Mechanisms that maintain species isolation within sympatric congeners have attracted analysis in many kinds of organisms, but not in snakes. We studied two sibling species of amphibious sea snakes (Laticauda colubrina and L. frontalis) on the island of Efate, in the Pacific Ocean republic of Vanuatu. The two taxa are almost identical morphologically, except that L. colubrina grows much larger than L. frontalis. No natural hybrids have been reported, and geographic distributions of the two taxa suggest the possibility of sympatric speciation. Our fieldwork shows that the two taxa are often syntopic and overlap in breeding seasons. Behavioral studies in outdoor arenas show that the separation between these two taxa is maintained by species-specific cues that control male courtship. Males of both species courted conspecific females but not heterospecific females. The proximate mechanism driving this separation involves chemical cues. Adult females of both taxa possess distinctive lipids in the skin. Males directed courtship behavior (chin-pressing) to hexane-extracted samples of lipids from conspecific but not heterospecific females. Males of the dwarf species (L. frontalis) were more selective courters than were those of the larger taxon (L. colubrina), perhaps because a preference for courting larger females means that L. colubrina males would be unlikely to court L. frontalis–sized (i.e., small) females even in the absence of pheromonal barriers.

Cheilostomatous Bryozoa from Vanuatu

The present account of some Bryozoa from Vanuatu is the first study of reef-flat species from the eastern Coral Sea. Based on samples collected from several shallow water localities on the island of Efate, a total of 92 species is described, including a new family, three new genera and 20 new species. Some of the newly recognized species are the result of taxonomic revision stimulated by these new samples, while others are entirely new to science. Of the new taxa described here, 16 are presently known only from Vanuatu. The total number of species recorded does not accurately represent the true taxonomic diversity of the Cheilostomatida of Vanuatu, and further sampling, at other localities and in other habitats, is needed before it can be reasonably estimated. The fauna is predominantly Indo–West Pacific in character with a high proportion of species apparently known only in the Southwest Pacific.

Cheilostomatous Bryozoa from Vanuatu

Abstract The present account of some Bryozoa from Vanuatu is the first study of reef-flat species from the eastern Coral Sea. Based on samples collected from several shallow water localities on the island of Efate, a total of 92 species is described, including a new family, three new genera and 20 new species. Some of the newly recognized species are the result of taxonomic revision stimulated by these new samples, while others are entirely new to science. Of the new taxa described here, 16 are presently known only from Vanuatu. The total number of species recorded does not accurately represent the true taxonomic diversity of the Cheilostomatida of Vanuatu, and further sampling, at other localities and in other habitats, is needed before it can be reasonably estimated. The fauna is predominantly Indo–West Pacific in character with a high proportion of species apparently known only in the Southwest Pacific.

Japanese Jomon sherds in artifact collections from Mele Plain on Efate in Vanuatu

AbstractFourteen cord‐marked sherds collected from the surface of yam gardens on Mele Plain near Port Vila on the island of Efate in Vanuatu are unlike any known prehistoric wares from Pacific islands. Based on typological analysis, comparative petrographic study of sand tempers supplemented by microprobe analysis of characteristic microperlite sand grains, and thermolumescence dating of key examples, we believe these sherds were made during the Early Jomon period in Aomori Prefecture near the north tip of Honshu. Although we are unable to specify the time or means of their introduction into Vanuatu, the sherds cannot represent indigenous pottery and are not part of the Oceanian ceramic legacy.

The Changing Coastline at Mele Beach, Vanuatu

This article examines research work done by secondary school students on a small stretch of coastline on the tropical Pacific island of Efate, in Vanuatu, In the study area, there is clear evidence of regular short-term changes in longshore drift and in the extent to which the river mouth is deflected. Such changes are related to seasonal variations in the prevailing winds. In the longer term, although Efate island is being affected by tectonic uplift, it would appear that the coastline and sand-spit in the study area are degrading, possibly as a result of recent severe tropical cyclones and of human impacts on natural beach processes.

A tilt and seismicity episode in the New Hebrides (Vanuatu) Island Arc

Tilt and seismicity have been monitored in the central New Hebrides island arc since 1978 using bench mark arrays, long tube water tiltmeters, borehole tiltmeters, and a local seismometer network. Releveling of the bench mark array on Efate island in late November 1986 revealed a 10 μrad tilt up to the NNW since the previous leveling in April 1986. The tilt event was preceded by a magnitude 5.9 thrust event that occurred on October 25, 1986, at a depth of 48 km and about 11 km NW of the tiltmeter instruments. Six days later, a shallow (&lt;20 km) swarm of earthquakes occurred 12 km NNW of the tiltmeter instruments and 5 km north of the epicenter of the magnitude 5.9 earthquake. Closely coincident in time with the swarm, a 5 μrad tilt up to the NNW that occurred over a period of 5 days was recorded on both the 100 m baseline water tube tiltmeter and the borehole bubble level tiltmeter. A composite focal mechanism of 191 earthquakes selected from the swarm indicates a thrust mechanism with some component of strike slip. Calculations show that the seismic slip associated with a swarm of this magnitude is apparently inadequate to cause the observed surface deformation. Two similar shallow swarms in November 1987 and July 1988 have occurred within 15 km of the 1986 swarm but with no apparent surface deformation. The most likely explanation, supported by simple modeling, is that the swarm and tilt are the result of a magmatic intrusion from island arc volcanism. An alternate hypothesis is that both the seismicity and the tilt are due to an episode of largely aseismic creep in the upper crust.

Patterns of seismicity associated with asperities in the Central New Hebrides Island Arc

In the central part of the New Hebrides Island Arc (Efate ‐ Malekula region, 16°S–18.6°S) a sequence of moderate sized earthquakes, their aftershock sequences, and other clusters of small earthquakes together form an intricate but coherent time‐space pattern that probably reveals a major asperity complex along the interplate boundary of the subduction zone. This pattern is determined by study of data from a local network. The sequences, including one event with magnitude Mw 7.1, eight events with magnitudes Mw between 5.8 and 6.3, and nearly 13,000 smaller events, occurred during the six year period 1978–1984. The seismicity is very unevenly distributed in space: a sharply defined east‐west line near 17.2°S separates the very active Efate region to the south, where nearly 10,500 earthquakes occurred, from the less active Malekula region to the north, where less than 2,500 earthquakes occurred during the six year period. In the Efate region several spatial patterns are highlighted. First, the seismic regimes of the updip and the downdip part of the interplate boundary are different. The updip part is characterized by a low background activity and main shocks with large aftershock zones, while the downdip part is characterized by a very high level of background activity and main shocks with much smaller aftershock zones or no aftershocks. This difference in seismic regimes suggests that asperities are located in the updip part of the interplate boundary, while the downdip part may slip predominantly by creep. A creep episode may have been responsible for the tilt signal observed by periodic relevelings of a 1‐km‐aperture network of benchmarks on Efate Island. Second, specific locations along the interplate boundary are identified either as sites of very intense and repeatedly activated concentrations of hypocenters or as sharp boundaries limiting the spatial development of aftershock zones. Two areas of concentrated activity particularly stand out; one located in the updip part of the interplate boundary and the other in the downdip part. Most of the clustered activity that occurred during the six years of observation is concentrated in these two areas. Four boundaries limiting the spatial development of aftershock zones are located in the updip part of the interplate boundary. One of these boundaries coincides with one of the areas of intense activity. Epicenters of moderately large events that occurred in the region since 1960 are also concentrated along the boundaries. The zones of concentrated activity and the boundaries limiting the development of aftershock zones can be interpreted either as locations of asperities or as edges of asperities. An alternative interpretation is that a giant asperity is located in the Malekula region, with the different spatial patterns observed in the Efate region being interpreted as the southern edge of that asperity, a transition zone between a locked part to the north and normal subduction to the south. Study of the temporal patterns of the seismicity shows that the main shocks in the downdip part of the interplate boundary are not preceded by obvious long‐term (months to year) nor short‐term (days to week) precursory activity. In the updip part of the interplate boundary, short‐term foreshocks preceded each main shock, but only one of these foreshock sequences is outstanding. Although no clear cyclic pattern related to the main shocks is evident, clustered activity that occurred in the two zones of concentrated activity and two other zones located in the back‐arc region are correlated in time with the occurrence of the major sequences located in the updip part of the interplate boundary. Activation of these four zones always follows the sequences in the updip part of the interplate boundary with varying time intervals (days to months). These four zones are also sometimes activated before sequences in the updip part of the interplate boundary. In particular, one of the zones of concentrated activity shows possibly repeated, long‐term (few months) precursory activity. This phenomenon could be an indicator of increasing probability of occurrence of main events in the updip part of the interplate boundary.

Studies of crustal converted waves using short-period seismograms recorded in the Vanuatu Island arc

AbstractOn three-component, short-period, digital array recordings, S to P converted phases from three major crustal discontinuities beneath Efate Island are identified between the primary P and S arrivals. The time differences between the main S arrival and these converted phases (Sp1, Sp2, and Sp3) provide constraints on the crustal structure beneath Efate Island. A crustal model with three layers over a half-space is determined, which is consistent with the results of a published refraction experiment in the southern Vanuatu (formerly New Hebrides) island arc.

The chemistry and hydrology of thermal springs on efate, vanuatu, sw pacific

Two zones of geothermal spring activity on the island of Efate are described. The hydrothermal systems are associated with a deep-seated graben through Pleistocene volcanics and fringing reef limestones. The Teuma group of springs have temperatures up to 59°C and discharge around 1 MW of heat, although total discharge into rivers is estimated from conductivity changes to be 10 MW. The hydrochemistry and stable isotope hydrology of these springs indicate that there are two thermal components: residual sea-water with estimated base temperature no more than 114°C and a less saline thermal water which has a much smaller surface discharge but is indicated by cation and SiO 2, geothermometry to have a base temperature up to 218°C. The Takara group of springs discharge in the coastal reef limestone where the meteoric water table intersects the ground surface; the proximity of this thermal water table also gives rise to an expanse of “hot ground” inland of the spring line. The excess heat flow from this system is around 20 MW, and varies according to the seasonality of fresh-water recharge and flux. A heat source at depth to the landward side of the thermal area is indicated. The hydrochemistry of the Takara system shows that it comprises sea-water, possibly mixed with meteoric water prior to circulation in the thermal reservoir. Mg 2+ and SO 2− 4 are strongly depleted in the thermal water relative to unreacted sea-water; however there is no detectable δ 18O shift which suggests a high water:rock ratio in the thermal reservoir. Quartz geothermometry indicates a base temperature up to 174°C which is similar to that indicated by cation geothermometry although the unusual absence of K + enrichment casts some doubt on use of the Na—K—Ca method. The interpretation emphasizes the need to examine and understand alteration mineralogy in order to place more confidence in geothermometry and to obtain more information on evolution of the geothermal systems. No drilling has yet taken place and much of the reservoir geology and description is speculation. The Teuma system probably comprises circulation in fractured basalt dykes associated with graben activity, and flow may therefore be very limited at depth. The Takara system has some similarities with other marine systems, mostly at oceanridge locations, where sea-water circulates convectively in basalts with a regionally-high geothermal gradient.

Leveling arrays as multicomponent tiltmeters: Slow deformation in the New Hebrides Island Arc

Two benchmark arrays located on the islands of Santo and Efate in the New Hebrides Island Arc have been releveled 2 to 4 times per year during the past five years (1975–1980). Each array is thereby used as a multicomponent tiltmeter. The arrays are located within 35–50 km of the interplate thrust zone of this convergent plate boundary. Each array has an aperture of about 1 km and in addition contains small subarrays with apertures of about 70 m. This configuration leads to a resolving power (for tilt) of about one microradian. The most important result of this study is that, at the Devils Point array on Efate Island, there has been a consistent tilting down of about five microradians in a direction subparallel to the strike of the arc. This tilting is clearly resolved by both the large array and by the small aperture sub‐arrays. The observations are accounted for by a combination of planar tilting and random error consistent with the observed misclosures. Although tilting is clearly established at the Devils Point array, it is not possible at this stage to establish a unique cause for the observed tilt. Hypotheses consistent with the tectonic setting include interseismic strain accumulation associated with the earthquake cycle of loading and interplate boundary rupture, deformations near a transition between a creeping and a locked segment of the interplate boundary, and near surface deformations associated with magmatic activity and/or block movements also reflected in the pattern of faulting of the uplifted Holocene coral terraces. At the second array at Ratard (Santo Island) no tilt trend clearly emerges from the noise level. However, two marginally significant tile excursions precede in each case large earthquakes located several hundred km north of the array. At the Ratard array the ground noise (small wavelength elevation disturbances and benchmark instability) contributes to residuals almost as much as the measurement error, thereby degrading the threshold level for detection of tilt signals. The difference between the two arrays is not clearly established but seems to reflect an inherently larger level of short wavelength ground noise associated with geological properties of the Ratard site.