West Pacific Area Research Articles

Numerical investigation of the effective receptive field and its relationship with convolutional kernels and layers in convolutional neural network

The receptive field (RF) plays a crucial role in convolutional neural networks (CNNs) because it determines the amount of input information that each neuron in a CNN can perceive, which directly affects the feature extraction ability. As the number of convolutional layers in CNNs increases, there is a decay of the RF according to the two-dimensional Gaussian distribution. Thus, an effective receptive field (ERF) can be used to characterize the available part of the RF. The ERF is calculated by the kernel size and layer number within the neural network architecture. Currently, ERF calculation methods are typically applied to single-channel input data that are both independent and identically distributed. However, such methods may result in a loss of effective information if they are applied to more general (i.e., multi-channel) datasets. Therefore, we proposed a multi-channel ERF calculation method. By conducting a series of numerical experiments, we determined the relationship between the ERF and the convolutional kernel size in conjunction with the layer number. To validate the new method, we used the recently published global wave surrogate model for climate simulation (GWSM4C) and its accompanying dataset. According to the newly established relationship, we refined the kernel size and layer number in each neural network of the GWSM4C to produce the same ERF but lower RF attenuation rates than those of the original version. By visualizing the gradient map at several points in West African and East Pacific areas, the high gradient value regions confirmed the known swell sources, which indicated effective feature extraction in these areas. Furthermore, the new version of the GWSM4C yielded better prediction accuracy for significant wave height in global swell pools. The root mean square errors in the West African and East Pacific regions reduced from approximately 0.3 m, in the original model to about 0.15 m, in the new model. Moreover, these improvements were attributed to the higher efficiency of the newly modified neural network structure that allows the inclusion of more historical winds while maintaining acceptable computational consumption.

Transcriptome assemblies of two deep-sea octocorals Calyptrophora lyra and Chrysogorgia stellata from West Pacific seamount, Godin Guyot.

This is the first report of the transcriptome assemblies of the deep-sea octocorals Calyptrophora lyra and Chrysogorgia stellata, which were collected in a survey of the West Pacific seamounts area. We sequenced the transcriptomes of C. lyra and C. stellata using the Illumina NovaSeq 6000 System. De novo assembly and analysis of the coding regions predicted 193,796 unigenes from the total 116,441,796 reads of C. lyra and 235,513 unigenes from the total 122,031,866 reads of C. stellata. Our data are a valuable resource with which to understand the ecological and biological characteristics of the West Pacific deep-sea corals. The data will also contribute to the study of deep-sea environments as extreme and limited habitats and provide direction for future research and further insight into the organismal responses of deep-sea corals to environmental changes.

Dengue and Dengue Virus in Guangdong, China, 1978-2017: Epidemiology, Seroprevalence, Evolution, and Policies.

BackgroundGuangdong is a hyperepidemic area of dengue, which has over 0.72 million cumulative cases within the last four decades, accounting for more than 90% of cases in China. The local epidemic of dengue in Guangdong is suspected to be triggered by imported cases and results in consequent seasonal transmission. However, the comprehensive epidemiological characteristics of dengue in Guangdong are still unclear.MethodsThe epidemiology, seroprevalence, molecular evolution of dengue virus, and the development of policies and strategies on the prevention and control of dengue were analyzed in Guangdong, China from 1978 to 2017.FindingsSeasonal transmission of dengue virus in Guangdong, China was mainly sustained from July to October of each year. August to September was the highest risk period of local dengue outbreaks. Most of the dengue cases in Guangdong were young and middle-aged adults. Five hundred and three fatal cases were recorded, which declined within the last two decades (n = 10). The serological test of healthy donors' serum samples showed a positive rate of 5.77%. Dengue virus 1–4 (DENV 1–4) was detected in Guangdong from 1978 to 2017. DENV 1 was the dominant serotype of dengue outbreaks from 1978 to 2017, with an increasing tendency of DENV 2 since 2010. Local outbreaks of DENV 3 were rare. DENV 4 was only encountered in imported cases in Guangdong, China. The imported cases were the main source of outbreaks of DENV 1–2. Early detection, management of dengue cases, and precise vector control were the key strategies for local dengue prevention and control in Guangdong, China.InterpretationDengue has not become an endemic arboviral disease in Guangdong, China. Early detection, case management, and implementation of precise control strategies are key findings for preventing local dengue transmission, which may serve for countries still struggling to combat imported dengue in the west pacific areas.

Changes in marine resource consumption over the past 5000 years in southwestern Taiwan revealed by fish otoliths

Coastal prehistoric settlement is a prominent topic in archaeology and is often associated with marine food supply for subsistence. In Taiwan and the tropical West Pacific area, early humans have relied on marine resources since the Palaeolithic period. However, in general, understanding past marine subsistence in Taiwan is impeded by scarce data on animal remains. This study investigated the change in fish consumption of prehistoric humans in southwest Taiwan over time using 1300 fish otoliths collected at archaeological sites in the Tainan Science Park. The investigated period was 5000 to 300 years ago, and two of the earliest currently-known Austronesian settlements in Taiwan, the Nankuanli and Nankuanli East sites, were included. In general, the abundance of otoliths declined over time. Our findings indicate that people of the Early and Late Neolithic preferred coastal fish, whereas people in the Iron Age preferred brackish and lagoonal fish. Fish assemblage was dominated by Larimichthys crocea (Richardson, 1846), and we use this species to compare the otolith size distribution through distinct periods. The comparison revealed an increase in fish size through time. We suggest that the changes in abundance and composition of the fish consumed by the prehistoric people were driven by the gradual seaward distancing of the shoreline, and the hypothesis that overfishing occurred in prehistoric southwestern Taiwan was rejected. Finally, the pronounced preference for the large yellow croaker may corroborate the theory of mainland-Chinese origins of the Austronesian speaking peoples.

Seasonal and Inter-Annual Variations of Stable Isotopic Characteristics of Rainfall and Cave Water in Shennong Cave, Southeast China, and Its Paleoclimatic Implication

Speleothem calcite stable oxygen isotope (δ18OC) is one of the most widely used proxies in paleoclimate research, and understanding its seasonal-annual variability is very significant for palaeoclimate reconstruction. Five-year precipitation and karst cave water from 2016 to 2021 were monitored in Shennong cave, Jiangxi Province, Southeast China. The local meteoric water line (LMWL) is δD = 8.20 × δ18O + 13.34, which is similar to the global meteoric water line. The stable hydrogen and oxygen isotope (δD and δ18O) characteristics of precipitation and cave water were studied. δ18O and δD of precipitation and cave water show obvious seasonal variations. Lower precipitation δ18O and δD generally occur during summer and autumn compared with higher δ18O and δD values during winter and spring. Meanwhile, low precipitation δ18O values do not only appear in June–July when precipitation is the highest of the year but also appear in August–September when precipitation is limited. The back-trajectory analysis of monsoon precipitation moisture sources shows that the moisture uptake regions vary little on inter-annual scales; the water vapor of rainfall in June–July comes from the South China Sea and the Bay of Bengal, while the moisture source in August–September is mainly from the West Pacific and local area. The El Niño-Southern Oscillation is an important factor affecting the value of δ18O by modulating the percentage of summer monsoon precipitation in the annual precipitation and moisture source. The relationship between amount-weighted monthly mean precipitation δ18O and Niño-3.4 index shows that the East Asian summer monsoon (EASM) intensifies during La Niña phases, resulting in more precipitation in monsoon season (May to September, MJJAS) and lower δ18O values, and vice versa during El Niño phases.

Interpretable tropical cyclone intensity estimation using Dvorak-inspired machine learning techniques

The intensity of a tropical cyclone is correlated strongly to the damage it causes when it makes landfall. Most of the time, tropical cyclones are located over the open ocean, where direct intensity measurements are difficult to obtain. An alternative approach is to estimate the tropical cyclone intensity indirectly from satellite images. In this case, there are two key points to consider: spatial and temporal relationships. For spatial relationships, the basic assumption is that cyclones with similar intensities have similar patterns. Thus, researchers can estimate intensity using pattern extraction and investigating similarities. For temporal relationships, the intensity of the cyclone is assumed to change smoothly, as a tropical cyclone is a continuous weather phenomenon. Thus, satellite images belonging to the same tropical cyclone should have a temporal (chronological) relationship with one another, meaning that the estimated intensity value of subsequent images should not change too drastically. In this research, we take advantage of these two key points and use random walk with a restart model to discover hidden correlations between target and historical cyclone images to estimate their intensity. We then use machine learning models to determine the temporal relationships among cyclone images, smoothing the prediction of the tropical cyclone event as a whole. Finally, our results show 15.77-knot root-mean-square error (RMSE) for the intensity estimation of tropical cyclones in the West Pacific Basin area.

Allied air intelligence in the South West Pacific Area, 1942-1945

ABSTRACT This article provides the first account of air intelligence in the South West Pacific Area during the Second World War. Centring on the organisational aspects of intelligence-gathering, analysis, and dissemination, it brings the Directorate of Intelligence within the combined Royal Australian Air Force-US Army Air Force Allied Air Forces into sharp focus. This article argues that Australian-American cooperation in air intelligence was shaped by strategic circumstances, the balance of Allied air forces in the theatre, and personal relations between intelligence personnel. Though cooperation in air intelligence largely ended on a sour note in late 1944 when the Australians were largely excluded from the US-led second Philippines campaign and the Directorate of Intelligence was essentially dissolved, this article demonstrates that the Directorate became a sophisticated, if under-appreciated, intelligence organisation by mid-1943.

Dengue and Dengue Virus in Guangdong, China, 1978-2017: Epidemiology, Seroprevalence, Evolution and Policies

Background: Guangdong is a hyper-epidemic area of dengue, with accumulated over 0.72 million cases within the last four decades, accounting for more than 90% of cases in China. Methods: The epidemiology, seroprevalence, molecular evolution of dengue virus and the development of policies and strategies on prevention and control of dengue were analyzed in Guangdong, China from 1978 to 2017. Findings: The seasonal endemic of dengue in Guangdong, China was mainly sustained from July to October of each year. Young and middle-aged people over 18 years old were the most affected populations. Serological test of healthy donors’ serum samples showed a positive rate of 5.77%. All serotypes of DENV (1-4) were detected in Guangdong. DENV1 was the dominant serotype of dengue outbreaks, while with an increasing tendency of DENV 2 since 2010. Local outbreaks of DENV 3 were rare. DENV 4 was only encountered in imported cases. The imported cases were the main source of outbreaks of DENV 1-2. Early detection, management of dengue cases and precise vector control were the key strategies for local dengue prevention and control in Guangdong, China. Interpretation: Localization of dengue is still not established in Guangdong. Early detection, case management and implement of precise control strategies are key findings for preventing local dengue transmission, which may serve for countries still struggling to combat imported dengue in west pacific areas. Funding Information: The National Key Research and Development Program of China (2020YFC1200104) and The Guangzhou Science and Technology Program (201904010012). Declaration of Interests: The authors declare no conflicts of interest. Ethics Approval Statement: The serum sampling protocol from dengue cases and healthy donors was approved by the Ethics Committee of the Guangdong CDC. All associated procedures were performed according to the humanization regulations. Patients' information was collected from local hospitals. All subjects provided written informed consent.

Анализ деятельности российского рыбопромыслового флота за пределами ИЭЗ России для минимизации потенциального ННН- промысла и воздействия на уязвимые морские экосистемы (Часть 2)

Russia is now on the 4th place in terms of total actual catch in the world.
 Despite the fact that the main part of the Russian catch is in the Russian
 exclusive economic zone (EEZ), many companies have started to look for
 new fishing areas and targets beyond the waters of national jurisdiction
 (ABNJ). Our analysis shows that the largest share of fish harvested by
 Russia outside its EEZ is in NEAFC areas, the North West Pacific area is quite
 promising as well. Preliminary analysis showed some signs of insufficiently
 controlled activity of the Russian fleet in the areas of ABNJ. This requires
 additional efforts to improve the monitoring system, especially in "restricted
 areas”, marine protected areas (MPAs) and areas of reproduction.

Influence of Latitude on the Prevalence of Kawasaki Disease: A Retrospective Cohort Study from the Taiwan National Health Insurance Database and Review of the Literature.

Background: Countries at higher latitudes have higher incidence rates of Kawasaki disease (KD) than do countries at lower latitudes in the Asian and West Pacific area. However, the precise influence of latitude on KD incidence rates requires further clarification. Methods: We searched the Longitudinal Health Insurance Database 2005 to retrieve patients’ medical records from 1996 to 2009. The patients with KD were categorized as living in northern, middle, and southern Taiwan; the period prevalence of KD for each area was determined. Climate variables, including temperature, sunshine duration, precipitation, and relative humidity, were collected from the Taiwan Central Weather Bureau. The effect of latitude on the period KD prevalence and the correlation between climate variables and KD prevalence were calculated. Results: After patients without complete data excluded, a total of 61,830 children up to 10 years old were retrieved, from which 404 patients with KD were recognized. The period prevalence of KD increased significantly with latitude (p = 0.0004). Climate variables associated with high temperature demonstrated a connection with KD prevalence; however, this correlation was not statistically significant. Conclusions: Our study demonstrated that higher latitude is associated with a higher KD prevalence in Taiwan.

Revealing the distinct habitat ranges and hybrid zone of genetic sub-populations within Pseudo-nitzschia pungens (Bacillariophyceae) in the West Pacific area

Genetic sub-populations (clades) of cosmopolitan marine diatom Pseudo-nitzschia pungens might have distinct habitats, and their hybrid zone is suspected in higher latitude area of the West Pacific area, however, it is still unrevealed because of technical difficulties and lack of evidences in natural environments. The aim of this study is to investigate the habitat characteristics of each clade of P. pungens on geographical distribution with the habitat temperature ranges of each clade and to reveal their hybrid zone in the West Pacific area. We employed the 137 number of nucleotide sequences of P. pungens and its sampling data (spatial and temporal scale) originated from the West Pacific area, and used field application of qPCR assay for intra-specific level of P. pungens. Only two genotypes, clade I and III, were identified in the West Pacific area. Clade I was distributed from 39 to 32.3°N, and clade III were from 1.4 to 34.4°N. The estimated habitat temperature for the clade I and clade III ranges were 8.1–26.9 °C and 24.2–31.2 °C, respectively. The latitudinal distributions and temperature ranges of each clade were significantly different. The qPCR assay employed, and results suggested that the hybrid zone for clade I and III has been observed in the southern Korean coasts, and clade III might be introduced from the Southern Pacific area. The cell abundances of clade III were strongly related with the higher seawater temperature and warm current force. This study has defined distinct habitat characteristics of genetically different sub-populations of P. pungens, and revealed its hybrid zone in natural environment for the first time. We also provided strong evidences about dispersion of the population of clade III to higher latitude in the West Pacific area.

A Study on the Strategic Implication of the Employment for the Amphibious Operational Forces of the U.S.S.R and USA During the WWII

Amphibious operation has developed with war history and it’s been conducting decisive role at the war. Amphibious troops did a key role when they swept the enemies and changed the war status from defensive to offensive direction. The U.S. and U.S.S.R fully understood the usefulness and flexibilities of amphibious troops. Although the U.S.S.R was known as a continental state, it built up amphibious power. On the contrary, the U.S. was a maritime nation it utilized the Marines when it expanded power to the West Pacific area. This article examined how the U.S. Marines and U.S.S.R Naval Infantry were employed during the World War II and found out its strategic implication. There were several similarities and differences between them. Both the U.S. and U.S.S.R. employed the amphibious troops when they tried to secure the lands and islands which were strongly defended by the enemies. The Marines and Naval Infantry showed off their sufficient capacities as an assault troops to recover the lost territories. In the beginning of the World War II the Marines and Naval Infantry of both countries hadnt full-fledged power to project, but they have expanded their size and grown their capacities during the wartime. However, there were lots of differences between them in conducting national strategy, building up the military powers, the strategy and tactics. The U.S. Marines usually did amphibious assault which was a large scale and from the long distance. In contrast, the U.S.S.R. Naval Infantry operated within the short distance and small groups but it developed the unique tactics called “Desant” that aimed at the enemy’s side and rear area attack to support the Army. It was totally different from the U.S.’s tactics. The former not only made progress amphibious doctrine, and built up enough ships but also supported by coordinated ship and air fire when they performed the mission. It usually conducted the amphibious operation by the systematic procedures from its first step to end. The latter made use of temporary amphibious ships, since improvisational assault and Navy’s fire support was limited. Although the U.S. Marines and U.S.S.R.’s Naval infantry were small sizes when compared with Army and Navy, they not only verified the efficiency but also showed the flexibilities of the amphibious troops. In this study we found that the U.S Marines and U.S.S.R Naval Infantry contributed the development of various amphibious operational skills and reminded the value of their existence. The amphibious troops can be easily affected by nation’s strategy and their performances when they try to survive as an independent military service.

Transcriptome analyses provide insights into the phylogeny and adaptive evolution of the mangrove fern genus Acrostichum.

The mangrove fern genus Acrostichum grows in the extremely unstable marine intertidal zone under harsh conditions, such as high salt concentrations, tidal rhythms and long-term climate changes. To explore the phylogenetic relationships and molecular mechanisms underlying adaptations in this genus, we sequenced the transcriptomes of two species of Acrostichum, A. aureum and A. speciosum, as well as a species in the sister genus, Ceratopteris thalictroides. We obtained 47,517, 36,420 and 60,823 unigenes for the three ferns, of which 24.39–45.63% were annotated using public databases. The estimated divergence time revealed that Acrostichum adapted to the coastal region during the late Cretaceous, whereas the two mangrove ferns from the Indo West-Pacific (IWP) area diverged more recently. Two methods (the modified branch-site model and the Kh method) were used to identify several positively selected genes, which may contribute to differential adaptation of the two Acrostichum species to different light and salt conditions. Our study provides abundant transcriptome data and new insights into the evolution and adaptations of mangrove ferns in the inhospitable intertidal zone.

MJO Propagation across the Maritime Continent in the ECMWF Ensemble Prediction System

AbstractThe characteristics of the MJO propagation across the Maritime Continent are investigated using a 20-yr reforecast dataset from the ECMWF ensemble prediction system. Analysis of the MJO events initialized over the Indian Ocean (phase 2) shows that the initial MJO amplitude and prediction skill relationship is not linear, particularly when the predictions start in moderate (between strong and weak) MJO amplitude category. To examine the key factors that determine the prediction skill, reforecasts in the moderate category are grouped into high- and low-skill events, and the differences in their ocean–atmospheric conditions as well as the physical processes during reforecast period are examined. The initial distribution of OLR anomalies in high-skill events shows a clear dipole pattern of convection with an enhanced convective anomalies over the Indian Ocean and strongly suppressed convective anomalies in the western Pacific Ocean. This dipole mode may support the MJO propagation across the Maritime Continent via the Rossby wave response and associated meridional moisture advection. Prominent ocean–atmosphere coupled processes are also simulated during the propagation of high-skill events. However, in low-skill events, the convective signal over the western Pacific is almost absent and less organized, and the ocean–atmosphere coupled processes are not simulated correctly. It is found that in both high- and low-skill events, the amplitude of the convective anomaly decreases significantly after about day 15, possibly due to the systematic mean model bias. A strong wet bias in the vicinity of the Maritime Continent, a cold SST bias in the equatorial Pacific, and associated circulation biases make the west Pacific area unfavorable for MJO propagation, thus limiting its prediction skill.

Early interglacial carbonate-dilution events in the South China Sea: Implications for strengthened typhoon activities over subtropical East Asia

A compilation of many late Quaternary marine sediment records from the northern South China Sea (SCS) continental slope confirms 15–50% reductions in sedimentary calcium carbonate concentrations between 11.0 and 8.5 ka BP in the early Holocene. This low carbonate% event occurred at a time when the regional sea level rose from −50 m to −10 m, which drowned large areas of continental shelves especially those near and within the Taiwan Strait. This event is associated with a significant increase in bulk sedimentation rates on the upper continental slope and the relative abundance of fine-grained detritus. Sediment provenance analyses suggest a dominant terrigenous input from Taiwan and a minor contribution from Luzon during the low carbonate% event, similar to the background terrigenous deposition in other periods of the Holocene. Two comparable low carbonate% events, respectively from the beginning of marine isotope stages 5.5 and 7.3, have also been recognized, pointing to similar causal factors. While carbonate dissolution and carbonate accumulation rate should not have been responsible, increased terrigenous input and dilution is considered as the main cause for the recurrent low carbonate% events in early interglacials. We further hypothesize that, during early interglacials, fluvial sediment discharge from Taiwan and Luzon intensified due to stronger typhoon activities, and massive fine-grained sediments from these two end members may have been transported to the northern SCS continental slope via surface and deep ocean currents. The conjecture of strengthened typhoon activities over East Asia during the early Holocene is supported by high ocean heat contents in the West Pacific Warm Pool area with the prevailing La Niña-like conditions.

To the Jungle Shore: Australia and Amphibious Warfare in the South West Pacific Area, 1942-1945

To the Jungle Shore: Australia and Amphibious Warfare in the South West Pacific Area, 1942-1945

Evolution of stamen number in Ptychospermatinae (Arecaceae): Insights from a new molecular phylogeny of the subtribe

The palm subtribe Ptychospermatinae (Arecaceae: Arecoideae) is naturally distributed in the South West Pacific area and contains 12 genera and around 60 species, including numerous popular ornamentals. Like many palms, Ptychospermatinae flowers are small, trimerous, unisexual and always grouped into inflorescences of various sizes. However they exhibit a wide diversity in stamen number (a few to several dozen or even hundreds) that is poorly understood from an evolutionary point of view. Although advances have been made in elucidating phylogenetic relationships within Ptychospermatinae, some relationships among and within genera still remain to be clarified. Here we used a combination of five nuclear markers (nrITS2, the conserved nuclear intron BRSC10 and three low copy genes, PRK, RPB2 and AGAMOUS) and three chloroplast markers (matK, ndhA and rps15-ycf1) to propose a new phylogenetic hypothesis for the subtribe. The combination of all these markers improved the resolution and robustness of phylogenetic relationships within the subtribe, allowing us to identify four major clades. This phylogenetic framework was used to examine the evolution of stamen number in the clade. The optimization of stamen number on the phylogeny highlighted the high level of interspecific variability, showing that the character is highly labile and raising questions about the evolutionary and functional significance of this lability.

Type studies of the polypores described by E.J.H. Corner from Asia and West Pacific areas VIII. Species described in Trametes (2)

Type examinations were conducted for 32 species of polypores described by E.J.H. Corner. The following new combinations are proposed: Antrodiella subligativa, Coriolopsis albobadia, C. suberosifusca, Datronia perstrata, D. sepiicolor, Fomitella malaysiana, Fomitopsis subvinosa, Microporus affinis-microloma, M. subvernicipes, Nigrofomes nigrivineus, Perenniporia rufidochmia, Polyporus polyporiformis, and Trichaptum molestum. The following species are accepted in the original genus: Trametes pallidilusor, the appropriate name for T. daedaleoides Corner (nom. illegit.), and T. rugosituba. Daedalea pseudodochmia was already combined with the proper genus. The following species are synonyms: Trametes microporoides and T. multiflabellata, synonyms of M. subvernicipes; T. papuasia, a synonym of Coriolopsis glabro-rigens; T. paxillosa, a synonym of Coriolopsis brunneoleuca; T. perpallida, a synonym of Skeletocutis nivea; T. primulina, a synonym of Coriolopsis sanguinaria; T. rigidiceps, a synonym of M. affinis-microloma; Trametes sublutea, a synonym of Fomitopsis spraguei; T. subincana and T. textulaminata, synonyms of D. pseudodochmia; and T. umbrinopallens, a synonym of T. lactinea. The following species are dubious because of the poor condition of specimens: T. tenacipora, T. turpis, and T. verticalis. No authentic specimens were traced for T. polyblastes, T. rubrigrisea, T. salina, T. sediliensis, and T. substrata. Descriptions and line drawings are given for the little-known species.

Modelling the impact of a La Niña event on a South West Pacific Lagoon

In view of increasing environmental awareness and biodiversity conservation, understanding the main forcing mechanism driving biogeochemical cycles in coral reefs and lagoon coastal areas is a priority. La Niña events cause unbalanced situations in the Equatorial Pacific and result in enhanced precipitation in South West Pacific coastal areas. We investigated the impact of heavy rainfalls during the 2008 La Niña event on the New Caledonia lagoon using a 3D coupled on-line hydrodynamic–biogeochemical model. Simulations and data showed that the whole lagoon was impacted by river inputs and stronger hydrodynamics, enhancing chlorophyll-a concentration by a factor between 1.7 and 1.9. The coupled model provided new insights into plume transport, highlighting that eastern plumes can be advected northwards or can reach the South West Lagoon, depending on the balance between regional, tide-induced, and wind-induced surface currents. It also provided a synoptic view of lagoon biogeochemical–hydrodynamic response, when remote sensing data are not available due to cloud coverage.

Pelagic larval duration of three amphidromous Sicydiinae gobies (Teleostei: Gobioidei) including widespread and endemic species

AbstractSicydiinae species have an amphidromous life cycle during which they undergo a pelagic larval phase allowing them to disperse through the ocean and to recruit in distant island rivers. Hypotheses for the differences observed in dispersal abilities between species include the variation in pelagic larval duration (PLD). However, the implication of the PLD as a proxy for explaining the dispersal ability of a species is not clear in the Sicydiinae subfamily. In this study, otolith microstructure of three Sicydiinae species was analysed. One of these species, Sicyopus zosterophorum, has a widespread distribution in the West Pacific area, whereas the other two species, Smilosicyopus chloe and Akihito vanuatu, are endemic to New Caledonia and to Vanuatu, respectively. Deposition of the daily growth increments on the otoliths of S. zosterophorum was validated using an alizarin complexone time marking technique. We estimated the PLD for the three species by counting the number of growth increments from the core to the metamorphosis check mark, and it was shorter than the one of previous studies on Sicydiinae species. The PLD of the widespread species, S. zosterophorum (54.6 ± 5.6 days), was similar to those of the endemic species, S. chloe (53.6 ± 5.7 days) and A. vanuatu (55.4 ± 7.5 days). Here, we show that in contrast to the most diverse Sicydiinae genus, Sicyopterus, the PLD could not explain endemism, and we must take into account other elements to explain the differences observed in the distribution range.