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The first survey of sea snakes (Elapidae, Hydrophiinae) at the remote Entrecasteaux atolls, Coral Sea, was conducted using remote unbaited 360° video cameras (RUV360), in 2021. We detected 49 snakes belonging to at least six species (Aipysurus duboisii, A. laevis, Hydrophis coggeri, H. macdowelli, H. major and H. ornatus) at the two largest atolls, Surprise and Huon. Three more are probably present (Emydocephalus annulatus, H. peronii, H. platurus), highlighting the richness of these atolls. No snakes were detected at neighboring smaller atolls. The lack of sea snake observations at the five small atolls may be due to the insufficient area of suitable habitat. Compared to assemblages sampled using the same method in New Caledonia (at Nouméa = A. laevis, E. annulatus, Laticauda sp., H. macdowelli, H. major, H. ornatus; at Touho = A. laevis, H. ornatus), and assemblages sampled with different methods at the Chesterfields (A. duboisii, A. laevis, E. annulatus, H. coggeri, H. laboutei, H. peronii, H. platurus), the Entrecasteaux atolls exhibit a high sea snake species richness. RUV360s appear to sample the diversity of sea snakes more effectively than did baited remote underwater video stations (BRUVS) within the Great Barrier Reef (which detected only A. laevis, H. curtus, H. ocellatus). [ABSTRACT FROM AUTHOR]

Life-history traits such as rates of growth, survival and reproduction can vary though time within a single population, or through space among populations, due to abiotically-driven changes in resource availability. In terrestrial reptiles, parameters such as temperature and rainfall generate variation in life-histories—but other parameters likely are more important in marine systems. We studied three populations of sea snakes (Emydocephalus annulatus) in adjacent bays in the IndoPacific archipelago of New Caledonia. The extreme philopatry of individual snakes allows us to unambiguously allocate each animal to one of the three populations. Although water temperatures and rainfall do not differ over this small scale, one site experiences more intense winds, restricting opportunities for foraging. Our 18-year mark-recapture dataset (> 1,200 snakes, > 2,400 captures) reveals significant divergence among populations in life-history traits. Survival rates and population densities were similar among sites, but snakes at the most wind-exposed site (Anse Vata) exhibited lower body condition, slower growth, less frequent production of litters, and smaller litters. Weather-driven variation in feeding rates thus may affect life-history traits of marine snakes as well as their terrestrial counterparts, but driven by different parameters (e.g., wind exposure rather than variation in temperatures or rainfall). [ABSTRACT FROM AUTHOR]

Evolutionary theory suggests that polymorphic traits can be maintained within a single population only under specific conditions, such as negative frequency-dependent selection or heterozygote advantage. Non-venomous turtle-headed sea snakes (Emydocephalus annulatus) living in shallow bays near Noumea in New Caledonia exhibit three colour morphs: black, black-and-white banded, and an intermediate (grey-banded) morph that darkens with age. We recorded morph frequencies during 18 consecutive years of surveys, and found that the numbers of recruits (neonates plus immigrants) belonging to each morph increased in years when that morph was unusually rare in the population, and decreased when that morph was unusually common. Thus, morph frequencies are maintained by negative frequency-dependent selection. We interpret the situation as Batesian mimicry of highly venomous sea snakes (Aipysurus, Hydrophis, Laticauda) that occur in the same bays, and range in colour from black-and-white banded to grey-banded. Consistent with the idea that mimicry may protect snakes from attack by large fish and sea eagles, behavioural studies have shown that smaller fish species in these bays flee from banded snakes but attack black individuals. As predicted by theory, mimetic (banded) morphs are less common than the cryptically-coloured melanic morph. [ABSTRACT FROM AUTHOR]

For sea snakes as for many types of animals, long-term studies on population biology are rare and hence, we do not understand the degree to which annual variation in population sizes is driven by density-dependent regulation versus by stochastic abiotic factors. We monitored three populations of turtle-headed sea snakes (Emydocephalus annulatus) in New Caledonia over an 18-year period. Annual recruitment (% change in numbers) showed negative density-dependence: that is, recruitment increased when population densities were low, and decreased when densities were high. Windy weather during winter increased survival of neonates, perhaps by shielding them from predation; but those same weather conditions reduced body condition and the reproductive output of adult snakes. The role for density-dependence in annual dynamics of these populations is consistent with the slow, K-selected life-history attributes of the species; and the influence of weather conditions on reproductive output suggests that females adjust their allocation to reproduction based on food availability during vitellogenesis. [ABSTRACT FROM AUTHOR]

In snakes, divergence in head size between the sexes has been interpreted as an adaptation to intersexual niche divergence. By overcoming gape-limitation, a larger head enables snakes of one sex to ingest larger prey items. Under this hypothesis, we do not expect a species that consumes only tiny prey items to exhibit sex differences in relative head size, or to show empirical links between relative head size and fitness-relevant traits such as growth and fecundity. Our field studies on the sea snake Emydocephalus annulatus falsify these predictions. Although these snakes feed exclusively on fish eggs, the heads of female snakes are longer and wider than those of males at the same body length. Individuals with wider heads grew more rapidly, reproduced more often, and produced larger litters. Thus, head shape can affect fitness and can diverge between the sexes even without gape-limitation. Head size and shape may facilitate other aspects of feeding (such as the ability to scrape eggs off coral) and locomotion (hydrodynamics); and a smaller head may advantage the sex that is more mobile, and that obtains its prey in narrow crevices rather than in more exposed situations (i.e., males). [ABSTRACT FROM AUTHOR]

Although sea snakes are important predators in coral reef ecosystems and have undergone substantial population declines in some areas, we have little robust information on life histories of these animals. Based on a 17-yr mark–recapture study of turtle-headed sea snakes (Emydocephalus annulatus) in New Caledonia (> 1200 individuals marked), we can confidently allocate ages to 539 individuals (1–11 yr of age). Using data for those snakes, we describe patterns of growth and reproduction. Using the entire data set, we also estimate annual rates of survival. One to three large offspring (300 mm snout–vent length [SVL]) are born after a prolonged (8-month) gestation. The young snakes grow rapidly until they are about 2 yr old (500 mm SVL), after which growth slows, especially in males. Most females begin reproducing at 3 yr of age, and they produce a litter (typically of two offspring) in about 2 out of every 3 or 4 yr thereafter. Annual survival rates are around 70%, but some individuals live for more than a decade. Overall, the life history of this species involves rapid growth and early maturation, followed by low but sustained reproductive output. Despite their relatively recent evolutionary origin, hydrophiine sea snakes are remarkably diverse in life histories as well as in morphologies and diets. Hence, even closely related taxa may differ substantially in their vulnerability to threatening processes. [ABSTRACT FROM AUTHOR]

Tidal cycles are known to affect the ecology of many marine animals, but logistical obstacles have discouraged behavioural studies on sea snakes in the wild. Here, we analyse a large dataset (1,445 observations of 126 individuals) to explore tidally-driven shifts in the behaviour of free-ranging turtle-headed sea snakes (Emydocephalus annulatus, Hydrophiinae) in the Baie des Citrons, New Caledonia. Snakes tended to move into newly-inundated areas with the rising tide, and became more active (e.g. switched from inactivity to mate-searching and courting) as water levels rose. However, the relative use of alternative habitat types was largely unaffected by tidal phase. [ABSTRACT FROM AUTHOR]

Without drastic efforts to reduce carbon emissions and mitigate globalized stressors, tropical coral reefs are in jeopardy. Strategic conservation and management requires identification of the environmental and socioeconomic factors driving the persistence of scleractinian coral assemblages-the foundation species of coral reef ecosystems. Here, we compiled coral abundance data from 2,584 Indo-Pacific reefs to evaluate the influence of 21 climate, social and environmental drivers on the ecology of reef coral assemblages. Higher abundances of framework-building corals were typically associated with: weaker thermal disturbances and longer intervals for potential recovery; slower human population growth; reduced access by human settlements and markets; and less nearby agriculture. We therefore propose a framework of three management strategies (protect, recover or transform) by considering: (1) if reefs were above or below a proposed threshold of >10% cover of the coral taxa important for structural complexity and carbonate production; and (2) reef exposure to severe thermal stress during the 2014-2017 global coral bleaching event. Our findings can guide urgent management efforts for coral reefs, by identifying key threats across multiple scales and strategic policy priorities that might sustain a network of functioning reefs in the Indo-Pacific to avoid ecosystem collapse.