Chuuk Lagoon Research Articles

Reproductive condition of the black-lip pearl oyster Pinctada margaritifera during the lunar phase.

This study analyzed the relationship between the lunar phase and the reproductive cycle of Pinctada margaritifera inhabiting Weno Island, Chuuk Lagoon, Micronesia. We measured indicators of maturity (gonadosomatic index [GSI]and sexual maturation-related genes) and investigated changes in the gonadal maturity stages (GMS) of P. margaritifera over lunar cycle. GSI was higher around the full moon. GMS of P. margaritifera were classified as the early gametogenesis stage, ripe and spawning stage, and spent and degenerating stage. A large percentage of oysters was observed in the ripe and spawning stage at the first quarter moon in female and the full moon in male as well as in the spent and degenerating stages at the third quarter moon in both sexes. In addition, the expression of doublesex- and mab-3-related transcription factor 2 (DMRT2) in the male P. margaritifera black-lip pearl oyster was the highest during the full and third quarter moon phases, whereas no difference in expression was observed with the lunar phase in females. In contrast, the expression of vitellogenin (VTG) was the highest in female P. margaritifera during the first and third quarters. No difference in expression was observed according to the lunar phase in males. The results suggest that the lunar phase directly affects the expression of sexually mature gonads in P. margaritifera black-lip pearl oyster.

Identifying Meteorologic and Oceanic Conditions Contributing to a Unique Phytoplankton Bloom Occurrence in Micronesia during October 2013

On the first several days of October 2013, daily chlorophyll a (chl a) data acquired by the Moderate Resolution Imaging Spectroradiometer (MODIS) onboard the National Aeronautics and Space Administration (NASA) Aqua satellite detected a marked increase in chlorophyll a concentrations (chl a) in the vicinity of Chuuk Lagoon and the Federated States of Micronesia. Such an increase, likely indicative of a phytoplankton bloom, has not been observed in this location at any other time during the MODIS-Aqua mission, which commenced in 2002 and continues to present. Examination of sea surface wind data from the Modern Era Retrospective analysis for Research and Applications Version 2 (MERRA-2) reanalysis dataset indicated that the region experienced a sequence of alternating elevated and very low wind speed events prior to the observation of the bloom. The influence of the winds can be seen in MERRA-2 sea surface skin temperature data. Elevated windspeeds for several days likely induced a mixing of deeper waters with higher nutrient levels to the surface, which was followed by stratification and phytoplankton growth during low wind intervals and finally transport induced by a brief high windspeed event. Analysis of hourly MERRA-2 maximum windspeed data over a 40-year period indicated that this sequence was climatologically rare.

Are Sunken Warships Biodiversity Havens for Corals?

Coral reefs are threatened by climate change, overfishing, and pollution. Artificial reefs may provide havens for corals, both to escape warming surface waters and to assist in the geographic migration of corals to more habitable natural reef conditions of the future. The largest artificial reefs have been generated by nearly 2000 shipwrecks around the world, but the coral diversity on these wrecks is virtually unknown. Ship size and hull material, location relative to natural reef, time since sinking, ocean currents, and water depth may affect coral diversity. As a test of the biodiversity capacity of very large sunken structures relative to surrounding natural reef, we carried out technical diver-based surveys to quantify genus-level coral diversity on 29 warships sunk in Bikini Atoll and Chuuk Lagoon. We also assessed whether ship length, as an index of substrate availability, and water depth, as an indicator of light and temperature, can serve as predictors of coral diversity. We surveyed a total of 9105 scleractinian corals. The total number of genera identified at Bikini was 34, and at Chuuk it was 51, representing 67% and 72% of genera found on natural reefs at Bikini and Chuuk, respectively. Ship length, but not water depth, was positively correlated with relative abundance and richness at the genus level. Our results suggest that very large wrecks can serve as havens for reef-building corals with a broad genetic diversity, expressed at the genus level, commensurate with corals found on neighboring natural reefs. The role of large artificial reefs could include protecting coral biodiversity from warming surface waters.

Caulerpa Bikinensis (Chlorophyta) Preference for the Mesophotic Depths of Pacific Atolls1

The marine green alga Caulerpa bikinensis W. R. Taylor was described as a new species in 1950 from dredged specimens (37–57 m depth) from Bikini Atoll and Rongelap Atoll in the Marshall Islands. Its relative rareness in collections from waters less than 30 m deep from these atolls indicated that it favored the mesophotic coral ecosystem (MCE) at depths of 30–150 m. Published and unpublished records of this species over the past 70 years show its habitat preference on the seaward slopes of atolls and in lagoons. Observations were based on collections from Pacific atolls of the Marshall Islands, Tuamotu Islands, Chuuk State in the Federated States of Micronesia, Cook Islands, and Johnston Atoll, and on the deep lagoonal reefs of Palau. Caulerpa bikinensis has also been recorded in shallow waters 1 m deep in dark microcavities on lagoonal pinnacles at Takapoto Atoll (Tuamotu Islands) and in Chuuk Lagoon, and 2 m deep at Raroia Atoll (Tuamotu Islands). Caulerpa bikinensis favors the deeper depths of the MCE for its low light intensity rather than its cooler temperature, and definitely shows a strong affinity to the high energy seaward slopes of calcareous Pacific atolls.

Ticking ecological time bombs: Risk characterisation and management of oil polluting World War II shipwrecks in the Pacific Ocean

The Second World War in the Pacific has left a legacy of over 3800 wrecks on the ocean floor. These wrecks contain thousands of tons of oil and pose a risk to the marine environment. Estimates of current corrosion rates show many wrecks are at risk of structural collapse. However, the scale of threat posed by potentially polluting wrecks (PPW) to coastal ecosystems in the Pacific is largely unknown, due to the lack of data to inform risk.This paper presents a strategy aimed to prioritise, manage, and mitigate negative effects of oil spills posed by PPW in the Pacific, using an example in Chuuk Lagoon. Wrecks are assessed and prioritised by means of risk characterisation. Wrecks are surveyed using photogrammetry to assess hull integrity. Finally, recommendations are made for the production of bespoke management plans and risk reduction strategies that work towards safeguarding marine ecosystems and the livelihoods of coastal communities.

Annual Reproductive Cycle of the Neon Damselfish Pomacentrus coelestis, in Chuuk Lagoon, Micronesia

Annual Reproductive Cycle of the Neon Damselfish Pomacentrus coelestis, in Chuuk Lagoon, Micronesia

Diving under the radar: divers and submerged aircraft

ABSTRACT Recreational scuba diving has grown over the past six decades and interest in wreck diving has increased. This growth demands evidence-based management, and understanding diver behaviour is crucial to effective management. This paper presents the first formal study of diver behaviour on a particular class of underwater cultural heritage, World War II submerged aircraft at Chuuk Lagoon in the Federated States of Micronesia. Chuuk is a world-renowned dive tourism destination, providing divers access to an extensive collection of shipwrecks and a few submerged aircraft. Although it may be assumed that diver behaviour on shipwrecks and aircraft would be similar, this study identifies marked differences in diver behaviour between the two different types of wrecks. This may be due to their novelty or to their scale. The smaller and more human scale of aircraft may encourage tactile interaction, such as sitting in the cockpit. Restricted physical access increases the chances of accidental damage to the aircraft. The implication of these findings is that there are different needs for the management of shipwreck and aircraft diving, to protect both cultural heritage and dive tourism values of sites.

Are shared models always cultural models? A study of the cultural model of affect and emotion in Chuuk

This article investigates a theoretical tension in cultural models theory between their sharedness and their origin in social and culturally mediated experiences. To address this tension empirically, this article presents a mixed-methods analysis of the shared understanding of a typology of emotion in Chuuk Lagoon. Based on a review of contemporary theory, one would expect that while people in Chuuk would have distinct cultural models for specific culturally meaningful paradigmatic emotions, the shared model for the entire typology of emotion would be structured by two universal dimensions of core affect (arousal and hedonic quality). But this theoretical literature ignores the importance of an intersubjective dimension of prereflective experience. This dimension may be culturally muted in industrial, educated, and rich contexts where most prior research has been conducted but culturally emphasized in places like Chuuk. The mixed-methods analysis finds that an intersubjective dimension along with a hedonic quality dimension structures the shared model of a typology for affect and emotion in Chuuk, while the arousal dimension found elsewhere is muted. Thus, shared models of affect and emotion are cultural models both in terms of specific, culturally elaborated emotions and in terms of the cultural emphasis given to underlying affective and intersubjective dimensions.

Parashewanella tropica sp. nov., a mesophilic bacterium isolated from a marine sponge from Chuuk lagoon, Federated States of Micronesia, and emended description of the genus Parashewanella.

A mesophilic, straight-rod-shaped, non-flagellated bacterium, designated MEBiC05444T, was isolated from a marine sponge collected from Chuuk lagoon, Federated States of Micronesia. The strain was Gram-negative, catalase- and oxidase-positive, and facultative anaerobic. The isolate aerobically grew at 8-38 °C (optimum, 24-32 °C), pH 4.0-10.0 (pH 7.0-7.5) with an absolute requirement for Na+ up to 6 % (w/v) NaCl (2 %). Phylogenetic analyses based on 16S rRNA gene sequences revealed that MEBiC05444T belonged to the family Shewanellaceae, within the class Gammaproteobacteria. Strain MEBiC05444T showed highest 16S rRNA gene sequence similarity to Parashewanella curva C51T, followed by [Shewanella] irciniae UST040317-058T and Parashewanella spongiae HJ039T (98.9 %, 97.2 and 95.7 %, respectively). In the phylogenetic tree based on the 16S rRNA gene sequences, MEBiC05444T formed a cluster with P. curva C51T, but the average nucleotide identity value between the two strains was 82 %, thus confirming their separation at species level. The major fatty acids were iso-C15 : 0 (19.7 %), summed feature 3 (composed of C16 : 1 ω7c and/or C16 : 1ω6c; 16.1 %) and C17 : 1ω8c (10.2 %). The only detected respiratory quinone was ubiquinone Q-8. The major polar lipids were phosphatidylethanolamine, phosphatidylglycerol, diphosphatidylglycerol, three unidentified aminoglycolipids, two unidentified glycolipids, an unidentified aminoglycophospholipid and an unidentified lipid. The genomic DNA G+C content of strain MEBiC05444T was 40.8 mol%. Based on the results of polyphasic analysis, the strain represents a novel species of the genus Parashewanella, distinct from P. curva C51T, [Shewanella]irciniae UST040317-058T and P. spongiae HJ039T for which the name Parashewanellatropica sp. nov. is proposed with type strain MEBiC05444T (=KCCM 43304T=JCM 16653T).

Diatoms associated with seaweeds from Moen Island in Chuuk Lagoon, Micronesia

In order to contribute understanding of the biodiversity of seaweed-associated diatoms at Moen Island in Chuuk lagoon, Micronesia in the tropical western Pacific, we collected four macroalgae (Halimeda sp., Padina sp., Sargassum sp., Dictyota sp.) that were distributed throughout at 5 subtidal sites of reef flat. These are the first records of diatoms from Chuuk, Federated States of Micronesia. A total 148 taxa belonging to 30 families and 49 genera were briefly documented with the identification references, dimension and illustrations, but many taxa could only be identified to genus. There is much similarity to the flora of Guam, but 16 records are new for the region. Four nomenclatural changes were necessary in consequence of the findings of Ruck et al. (2016) on Surirellales and Rhopalodiales.

Assessing the Impact of Typhoons on Historic Iron Shipwrecks in Chuuk Lagoon Through Changes in the Corrosion Microenvironment

The corrosion microenvironment of a dozen Second World War iron shipwrecks in Chuuk Lagoon, Federated States of Micronesia, was investigated to see if there were any measurable changes caused by a recent major typhoon. Seven previously inspected wreck sites were used for calibration to assess the environmental impacts. Five new wrecks, including the Fumitzuki, a destroyer of the Imperial Japanese Navy, were assessed at up to twice the depth of previous studies. The new data showed that the logarithm of the corrosion rate falls linearly with depth to 36 m. Measurements of corrosion potentials, concretion thickness and pH showed that many of the vessels suffered partial deconcretion during the typhoon Maysak in April 2015 with concomitant increases in the rate of decay. Regrowth of the colonising marine organisms are presently ameliorating the impact of the typhoon.

The reproductive cycle of the humbug damselfish Dascyllus aruanus according to the changes in lunar phase in Micronesia

The moon is known to be an environmental factor that controls the reproductive cycle of fish, and fish have evolved a variety of reproduction patterns depending on the lunar phase. In this study, we examined the relationship between lunar phases and the reproductive cycle of the humbug damselfish Dascyllus aruanus inhabiting Weno Island, Chuuk Lagoon, Micronesia. We divided the one-month lunar cycle into eight phases, and measured the features of moonlight (peak wavelength and intensity) and indicators of fish maturity [gonadosomatic index (GSI) and sex hormones] in relation to the eight lunar phases. In addition, we investigated the daily rhythms of sex hormones in fish ovaries during the full moon phase. The results showed that the peak wavelength of moonlight was 430 nm (blue wavelength region) regardless of the lunar phase, and that moonlight intensity was highest during a full moon at 02:00. Furthermore, the GSI and sex hormones were both higher around the full moon phase. These findings support the hypothesis that humbug damselfish spawn once a month and that this event occurs at full moon, which is the phase of the moon with the strongest intensity. Based on these findings, we predict that blue wavelength, the dominant wavelength of moonlight, is one of the environmental factors influencing the monthly spawning of D. aruanus.

Length-weight relationships of six coral reef-fish species from Chuuk, Federated States of Micronesia

Length–weight relationships (LWR) were estimated for six reef species in Chuuk lagoon (Federated States of Micronesia) captured by commercial fishers. Specimens were sampled opportunistically over a period of 2 months between July and September 2014. Relationships include those for four common species not currently reported in FishBase (Caesio teres, Myripristis adusta, Lethrinus erythracanthus, and Chlorurus frontalis), and for two species with relationships based on just one or two samples (Scarus oviceps, and Plectropomus oligacanthus). While estimates for some species are tentative given limited size-range sampling, they still present an improvement in the currently available LWRs.

Complete mitochondrial genome analysis of Phascolosoma sp. (Sipuncula, Phascolosomatida, Phascolosomatidea) from Micronesia

In this study a Sipuncula species Phascolosoma sp. was collected from seagrass area from Chuuk lagoon Micronesia and its complete mitochondrial genome analyzed. This is the second complete mitochondrial genome record from the genus after Phascolosoma esculenta. The total length of mitochondrial genome of the species is 16,571 bp, which is longer than P. esculenta record. Also, locations of tRNA-Gly and putative control region are different between two records. Furthermore, phylogenetic relationship of Phascolosoma sp. are investigated due to protein-coding genes of mitochondrial genome. Due to the lack of recorded data, P. esculenta has been observed is the closest species to Phascolosoma sp. and they are belonging to the monophyletic group.

Influence of ambient water intrusion on coral reef acidification in the Chuuk lagoon, located in the coral‐rich western Pacific Ocean

AbstractWeekly carbonate chemistry condition data recorded between 2008 and 2014 in the Chuuk lagoon (7.3°N and 151.5°E) of the Federated States of Micronesia, located in the western Pacific Ocean, were analyzed. The results showed that, during periods of weak intrusion of ambient seawater from the surrounding open ocean, two internal biological processes (calcification and respiration) reinforced each other and together lowered the pH of the reef water for extended periods, ranging from a few to several months. The analysis indicated that reduced intrusion of ambient water is associated with periods of low wind speeds. Such conditions increase the residence time of reef water, thus promoting acidification by respiration and calcification. This phenomenon likely affects many other areas of the coral‐rich western Pacific Ocean, which contains 50% of global coral reefs and in which the degree of ambient water intrusion into the atolls has been shown to be closely associated with the El Niño–Southern Oscillation‐induced wind speed change.

In-situ Corrosion Measurements of WWII Shipwrecks in Chuuk Lagoon, Quantification of Decay Mechanisms and Rates of Deterioration

This paper is based on a series of measurements taken on WWII historic shipwrecks that resulted from the effects of Operation Hailstone in February 1944 on the Japanese merchant fleet which was assembled in Chuuk lagoon, Federated States of Micronesia. More than 65 shipwrecks and 250 aircraft were sunk during two main bombing raids. The vessels lost covered a wide range of underwater orientation and water depths and so provided a perfect suite of corrosion experiments. Since the fuel on board the aircraft was either readily burnt at the time or was lost through volatilisation, the wrecked planes present no pollution problems today. However the bunker fuel kept inside on-board storage tanks does present a real conservation management crisis. In-situ measurements on many vessels have determined how water depth, the localised wreck topography, dissolved oxygen levels, temperature and salinity affects the corrosion rate of cast iron and mild steel. Thus corrosion rates can be calculated with confidence.

Complete mitochondrial genome of Leptodius sanguineus (Decapoda, Xanthidae)

The complete mitochondrial genome sequenced from a xanthid crab, Leptodius sanguineus which was collected from a rocky intertidal area in Chuuk lagoon. The mitochondrial genome size of L. sanguineus evaluated as 15,480 bp with 33.6% A, 24% C, 11.2% G and 31.2% T and mitochondrial gene order of L. sanguineus is typical to brachyuran species. Phylogenetic analysis shows that the family Xanthidae has sister group relationship with a lineage including the families Portunidae and Menippidae in the subsection Heterotremata. This is the first report for the complete mitochondrial genome from the xanthid crabs.

The complete mitochondrial genome of Grapsus tenuicrustatus (Herbst, 1783) (Decapoda, Grapsidae)

A complete mitochondrial genome was sequenced from a grapsid crab, Grapsus tenuicrustatus (Herbst 1783), which was collected from a rocky intertidal zone of Chuuk lagoon. The size of mitochondrial genome is 15,858 bp with 31.9% A, 22.8% C, 12.2% G and 33.1% T distribution. Furthermore phylogenetic relationships of the Grapsoidea evaluated due to mitochondrial protein-coding genes. As per the obtained results, the families Grapsidae and Varunidae have sister group relationship in the superfamily Grapsoidea.

Reptiles of Uman District Islands (Southeastern Chuuk Lagoon and Kuop Atoll), Federated States of Micronesia

Thirteen species of reptiles are recorded from among 23 islands in the southeastern sector of Chuuk Lagoon and on adjacent Kuop Atoll (= Uman District islands), Federated States of Micronesia (FSM). They include two sea turtles, five geckos, five skinks, and one monitor lizard. None is endemic to Chuuk, and most are found widely throughout the western Pacific. Perochirus ateles was the most frequently encountered species, followed closely by Emoia boettgeri. Sea turtles are scarce due in large measure to indiscriminant harvesting of adults and eggs. The common house gecko, Hemidactyus frenatus, probably was introduced to Chuuk during post-World War II human-assisted transport to many Pacific islands, and Chuuk Islanders claim the Pacific monitor, Varanus indicus, was brought to Chuuk during the Japanese administration. The monitor lizard has apparently since been extirpated on the two Uman District islands where it was previously recorded. To what extent the other species colonized Chuuk islands by natural dispersal or human-assisted dispersal or a combination of the two is uncertain.

Reproductive characteristics of the humbug damselfish, Dascyllus aruanus, in Chuuk Lagoon, Micronesia

This study was conducted to investigate the reproductive characteristics of the humbug damselfish, Dascyllus aruanus, through the measurement of gonadosomatic indices (GSI) and histological examination of the gonads. Fish were collected from Chuuk Lagoon, Micronesia (7°27′N; 151°53′E), between August 2009 and July 2010. Overall, the functional sex ratio was approximately 1:1; however, there was a female bias in the smaller size range (35–40 mm standard length [SL]) and male bias in the larger size range (45–60 mm in SL). The process of oocyte development exhibited a group synchronous pattern, from the vitellogenic phase oocytes in the gonads following the two clutches of oocytes, as the primary growth stage and yolk vesicle stage. The testis with an ovarian lumen exists as a central slit, and the sperm ducts extend into the medial hilar region of the gonads, indicating that males of D. aruanus have a secondary testis of protogynous species. Monthly variations in the GSI and evolution of gonad status indicated that reproductive activity in this species occurs throughout the year in Chuuk Lagoon, Micronesia.