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Hong Yan - One of the best experts on this subject based on the ideXlab platform.
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the first detection of the madden julian oscillation signal in daily to hourly resolution proxy records derived from a natural archive of giant clam shell Tridacna spp
Earth and Planetary Science Letters, 2021Co-Authors: Hong Yan, Haobai Fei, Cheng-cheng Liu, Nanyu Zhao, Pengchao Zhou, Fei Liu, Yuanjian Yang, Wei Yang, John DodsonAbstract:Abstract The Madden-Julian Oscillation (MJO) is the most prominent mode of intraseasonal variability in the tropics which is responsible for much of the observed intraseasonal climate variance not only there but also in higher latitudes. The short time-span of modern instrumental data limits our understanding of the MJO and obtaining MJO information from natural archives could extend this greatly. Here a Giant Clam shell (Tridacna spp.) with a life span about two years (from January 29, 2012 to December 9, 2013) was collected from the northern South China Sea, in the western Pacific. Several daily to hourly resolution biological and geochemical proxy records, including the daily growth rate, hourly Fe/Ca, Sr/Ca and fluorescence intensity, were developed to compare these with local weather/climate records. Spectral analyses suggested that these ultra-high resolution proxy records can clearly record MJO variability in the tropics. The substantial connection between the proxy records and MJO possibly linking through the local effective solar radiation, SST, precipitation and wind speeds. This is the first record of the MJO signal in a natural paleoclimate archive. Our findings provide new insights to study the MJO beyond the instrumental records, and since fossil Tridacna shells from different geological times can be used to investigate the MJO under various climate conditions.
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Dynamic of Tridacna spp. population variability in northern SCS over past 4500 years derived from AMS 14C dating
The Science of the total environment, 2020Co-Authors: Cheng-cheng Liu, Hong Yan, Haobai Fei, Ge Shi, Peng Cheng, Hanfeng Wen, Shugang Kang, Willie Soon, John DodsonAbstract:Abstract The marine bivalve, Tridacna spp. is an iconic invertebrate of the Indo-Pacific coral reef communities from Eocene to present. However, field observations found that the population of Tridacna spp. has declined in recent decades and some species are now endangered in the northern South China Sea (SCS) of western Pacific, which are speculated to be connected with the human overfishing and/or climate changes. Thus distinguishing the impacts of human activities and climate changes on Tridacna spp. populations is essential for understanding the dynamic of Tridacna spp. population variability. Such effort will be important in launching conservation policies and restoring population. Here, extensive sampling was applied on sub-fossil Tridacna spp. shells at the North Reef of the northern SCS, and the long-lived (with a lifespan more than 30 years) Tridacna spp. population index (LTPI) over the past 4500 years was obtained based on the AMS14C dating method. The results show that LTPI has experienced several short-term collapses (shorter than 200 years) over the past 4500 years, which may be associated with excessive cold winter temperatures. Remarkably, LTPI usually recovered rapidly after the rewarming of temperatures, indicating a robust self-recruitment mechanisms in response to natural climate changes. However, the last catastrophic collapse of LTPI that occurred at around ~1820 CE – ~1900 CE didn't rebound despite the significant rise in temperature over the recent 100 years. The decoupling between LTPI and climate changes in recent hundred years was probably induced by the increased commercial fishing in the SCS, which has overwhelmed and exacerbated the self-recruitment mechanisms between Tridacna spp. population and climate changes.
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evidence from giant clam δ 18 o of intense el nino southern oscillation related variability but reduced frequency 3700 years ago
Climate of The Past, 2020Co-Authors: Xiaoming Sun, Hong Yan, Hai ChengAbstract:Abstract. Giant clams (Tridacna) are the largest marine bivalves, and their carbonate shells can be used for high-resolution paleoclimate reconstructions. In this contribution, δ18O shell was used to estimate climatic variation in the Xisha Islands of the South China Sea. We first evaluate sea surface temperature (SST) and sea surface salinity (SSS) influence on the modern resampled monthly ( r -monthly) resolution of Tridacna gigas δ18O shell . The results obtained reveal that δ18O shell seasonal variation is mainly controlled by SST and appears to be insensitive to local SSS change. Thus, the δ18O of Tridacna shells can be roughly used as a proxy of local SST: a 1 ‰ δ18O shell change is roughly equal to 4.41 ∘ C of SST. The r -monthly δ18O of a 40-year-old Tridacna squamosa ( 3673±28 BP) from the North Reef of the Xisha Islands was analyzed and compared with the modern specimen. The difference between the average δ18O of the fossil Tridacna shell ( δ18O = - 1.34 ‰) and the modern Tridacna specimen ( δ18O = - 1.15 ‰) probably implies a warm climate, roughly 0.84 ∘ C, 3700 years ago. The seasonal variation 3700 years ago was slightly lower than that suggested by modern instrumental data, and the transition between warm and cold seasons was rapid. Higher amplitudes of reconstructed r -monthly and r -annual SST anomalies imply an enhanced climate variability during this warm period. Investigation of the El Nino–Southern Oscillation (ENSO) variation (based on the reconstructed SST series) indicates reduced ENSO frequency but increased ENSO-related variability and extreme El Nino winter events 3700 years ago.
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A high-resolution δ18O record of modern Tridacna gigas bivalve and its paleoenvironmental implications
Palaeogeography Palaeoclimatology Palaeoecology, 2020Co-Authors: Hong Yan, Haobai Fei, Cheng-cheng Liu, Ge Shi, Enqing Huang, Yue Wang, Ergang Lian, Haowen DangAbstract:Abstract The lack of monthly-resolved paleoenvironmental records beyond the instrumental era hinders our full understanding of global climate dynamics. Tridacna gigas shells have a large potential to quantitatively document the variability of the ocean surface environment on time scales from daily to interannual in the past, while the applicability of the geochemical proxies of Tridacna gigas needs to be quantitively investigated. Here we establish a chronology for a Tridacna gigas shell from the southern South China Sea (SCS) by identifying daily growth laminae using a laser scanning confocal microscope (LSCM). Our high-resolution Tridacna gigas shell δ18Oshell record throughout 1989–2013 shows a high correlation with changes in local precipitation and the index of El Nino-Southern Oscillations (ENSO) on the interannual time scale. Together with observed sea surface temperature (SST), we calculated seawater δ18O (δ18Osw) and derived sea surface salinity (SSS) change in the southern SCS based on the Tridacna gigas shell δ18O record. Our salinity-budget calculation results suggest that the SSS variability in the southern SCS is predominantly affected by the vertical mixing and sea surface freshwater flux. Our study reveals that the Tridacna gigas shell is an ideal archive for high-resolution and quantitative paleoenvironmental reconstructions in tropical ocean regions, thus providing a new window to explore paleoenvironmental changes on annual and interannual time scales.
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temperature seasonality and enso variability in the northern south china sea during the medieval climate anomaly interval derived from the sr ca ratios of Tridacna shell
Journal of Asian Earth Sciences, 2019Co-Authors: Cheng-cheng Liu, Hong Yan, Haobai Fei, Ge Shi, Willie Soon, John Dodson, Wenchao ZhangAbstract:Abstract The nature of how the El Nino–Southern Oscillation (ENSO) and its seasonality respond to warmer climate is critical knowledge to predict future climates under the expected anthropogenic warming scenario. In this study, a sub-fossil Tridacna gigas specimen was collected from the northern SCS and AMS14C dating suggested that the animal lived around AD 1099, during the Medieval Climate Anomaly (MCA) interval, the most recent natural warm period of the late Holocene. Monthly Sr/Ca ratios were determined by the ICP-OES measurements and a 30-year long SST record was calculated based on a Sr/Ca-SST calibration equation. The results showed that the SST seasonality for this 30-year window around AD 1099 was about 3.11 °C, which is smaller than the modern warm period (i.e., about 4.36 °C for AD 1994 ∼ 2005 interval). This new result is consistent with another published Tridacna gigas record that was dated around AD 990 from the northern SCS. The signals of ENSO activity were also extracted from the reconstructed SST record and statistical analyses yielded 9 El Nino events and 8 La Nina events within the 30-year record, indicating that the frequency of ENSO activity around AD 1099 was similar to the modern instrumental period.
John Dodson - One of the best experts on this subject based on the ideXlab platform.
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the first detection of the madden julian oscillation signal in daily to hourly resolution proxy records derived from a natural archive of giant clam shell Tridacna spp
Earth and Planetary Science Letters, 2021Co-Authors: Hong Yan, Haobai Fei, Cheng-cheng Liu, Nanyu Zhao, Pengchao Zhou, Fei Liu, Yuanjian Yang, Wei Yang, John DodsonAbstract:Abstract The Madden-Julian Oscillation (MJO) is the most prominent mode of intraseasonal variability in the tropics which is responsible for much of the observed intraseasonal climate variance not only there but also in higher latitudes. The short time-span of modern instrumental data limits our understanding of the MJO and obtaining MJO information from natural archives could extend this greatly. Here a Giant Clam shell (Tridacna spp.) with a life span about two years (from January 29, 2012 to December 9, 2013) was collected from the northern South China Sea, in the western Pacific. Several daily to hourly resolution biological and geochemical proxy records, including the daily growth rate, hourly Fe/Ca, Sr/Ca and fluorescence intensity, were developed to compare these with local weather/climate records. Spectral analyses suggested that these ultra-high resolution proxy records can clearly record MJO variability in the tropics. The substantial connection between the proxy records and MJO possibly linking through the local effective solar radiation, SST, precipitation and wind speeds. This is the first record of the MJO signal in a natural paleoclimate archive. Our findings provide new insights to study the MJO beyond the instrumental records, and since fossil Tridacna shells from different geological times can be used to investigate the MJO under various climate conditions.
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Dynamic of Tridacna spp. population variability in northern SCS over past 4500 years derived from AMS 14C dating
The Science of the total environment, 2020Co-Authors: Cheng-cheng Liu, Hong Yan, Haobai Fei, Ge Shi, Peng Cheng, Hanfeng Wen, Shugang Kang, Willie Soon, John DodsonAbstract:Abstract The marine bivalve, Tridacna spp. is an iconic invertebrate of the Indo-Pacific coral reef communities from Eocene to present. However, field observations found that the population of Tridacna spp. has declined in recent decades and some species are now endangered in the northern South China Sea (SCS) of western Pacific, which are speculated to be connected with the human overfishing and/or climate changes. Thus distinguishing the impacts of human activities and climate changes on Tridacna spp. populations is essential for understanding the dynamic of Tridacna spp. population variability. Such effort will be important in launching conservation policies and restoring population. Here, extensive sampling was applied on sub-fossil Tridacna spp. shells at the North Reef of the northern SCS, and the long-lived (with a lifespan more than 30 years) Tridacna spp. population index (LTPI) over the past 4500 years was obtained based on the AMS14C dating method. The results show that LTPI has experienced several short-term collapses (shorter than 200 years) over the past 4500 years, which may be associated with excessive cold winter temperatures. Remarkably, LTPI usually recovered rapidly after the rewarming of temperatures, indicating a robust self-recruitment mechanisms in response to natural climate changes. However, the last catastrophic collapse of LTPI that occurred at around ~1820 CE – ~1900 CE didn't rebound despite the significant rise in temperature over the recent 100 years. The decoupling between LTPI and climate changes in recent hundred years was probably induced by the increased commercial fishing in the SCS, which has overwhelmed and exacerbated the self-recruitment mechanisms between Tridacna spp. population and climate changes.
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temperature seasonality and enso variability in the northern south china sea during the medieval climate anomaly interval derived from the sr ca ratios of Tridacna shell
Journal of Asian Earth Sciences, 2019Co-Authors: Cheng-cheng Liu, Hong Yan, Haobai Fei, Ge Shi, Willie Soon, John Dodson, Wenchao ZhangAbstract:Abstract The nature of how the El Nino–Southern Oscillation (ENSO) and its seasonality respond to warmer climate is critical knowledge to predict future climates under the expected anthropogenic warming scenario. In this study, a sub-fossil Tridacna gigas specimen was collected from the northern SCS and AMS14C dating suggested that the animal lived around AD 1099, during the Medieval Climate Anomaly (MCA) interval, the most recent natural warm period of the late Holocene. Monthly Sr/Ca ratios were determined by the ICP-OES measurements and a 30-year long SST record was calculated based on a Sr/Ca-SST calibration equation. The results showed that the SST seasonality for this 30-year window around AD 1099 was about 3.11 °C, which is smaller than the modern warm period (i.e., about 4.36 °C for AD 1994 ∼ 2005 interval). This new result is consistent with another published Tridacna gigas record that was dated around AD 990 from the northern SCS. The signals of ENSO activity were also extracted from the reconstructed SST record and statistical analyses yielded 9 El Nino events and 8 La Nina events within the 30-year record, indicating that the frequency of ENSO activity around AD 1099 was similar to the modern instrumental period.
Cécile Fauvelot - One of the best experts on this subject based on the ideXlab platform.
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Genome skimming resolves the giant clam (Bivalvia: Cardiidae: Tridacninae) tree of life
Coral Reefs, 2021Co-Authors: Edwin Y. W. Tan, Cécile Fauvelot, Z. B. Randolph Quek, Mei Lin Neo, Danwei HuangAbstract:Giant clams are conspicuous bivalves inhabiting Indo-Pacific reefs. Since Rosewater’s seminal paper in 1965, the number of giant clam species described or resurrected has exactly doubled. The increased number of species reported and accessibility to genetic material of rare or uncommon species therefore call for a reappraisal of the phylogenetic relationships within the Tridacninae subfamily. Here, we aim to reconstruct the evolutionary relationships among all 12 extant species by performing a comprehensive phylogenetic analysis of mitochondrial genome and nuclear 18S rRNA data from a combination of genome skimming, Sanger sequencing and previously published sequences. Comparing the mitogenomes among Tridacninae species, we report two new findings: (1) the T . crocea mitogenome length obtained here (18,266 bp) is shorter than previously known, and (2) the mitochondrial gene order in T . crocea and T . squamosa differs from the other species. Our phylogeny based on a concatenated 16-gene dataset (15 mitochondrial markers and nuclear 18S rRNA) reveals highly supported relationships within and between the three subgenera, Tridacna ( Tridacna ) , Tridacna ( Persikima ) and Tridacna ( Chametrachea ). Overall, the inclusion of new molecular markers greatly improves the confidence and support for the subfamily’s phylogeny. The availability of this comprehensive phylogenetic dataset serves as the foremost baseline of Tridacninae relationships to support future studies examining giant clam systematics, ecology and conservation.
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The forgotten giants of the Western Indian Ocean reefs
Journal of Biogeography News, 2020Co-Authors: Philippe Borsa, Cécile FauvelotAbstract:We addressed the evolutionary history of Tridacna giant clams by combining molecular phylogenies with the geographic distribution of lineages across the Indo-West Pacific, with a focus on the Western Indian Ocean (WIO). A giant clam initially identified as T. maxima was genetically distinct and identified as T. elongatissima, a long-forgotten species from Mozambique. Two nominal species endemic to the Mascarene basin, T. lorenzi and T. rosewateri were found to be a single and same, distinct species. Tridacna elongatissima turned out to be the sister species of T. squamosina, another recently resurrected species endemic to the Red Sea. The T. elongatissima-T. squamosina pair was itself sister to T. rosewateri, highlighting this part of the world as a hotspot of endemism for giant clams. With two unrelated lineages in the WIO, one of which was sister to a third lineage endemic to the Red Sea, lineage diversification patterns within the widespread T. maxima mirrored those of T. elongatissima, T. rosewateri and T. squamosina. The same geographic barriers and speciation processes may thus have acted repeatedly at different periods in the Pleistocene.
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Phylogeography of Noah’s giant clam
Marine Biodiversity, 2017Co-Authors: Cécile Fauvelot, Serge Andréfouët, Daphné Grulois, Josina Tiavouane, Colette Wabnitz, Hélène Magalon, Philippe BorsaAbstract:Noah’s giant clam (Tridacna noae), recently resurrected from synonymy with T. maxima, occurs from Christmas Island to the Northern Line Islands and from the Ryukyu Islands to New Caledonia. We used mitochondrial and microsatellite markers to investigate the phylogeographic structure and demographic history of T. noae over most of its geographical range. Results from the two types of markers reveal a consistent population structure, partitioning T. noae into three distinct lineages: (1) eastern half of the Indo-Malay archipelago and Western Australia, (2) Melanesia and Micronesia, and (3) Central Polynesia. Demographic expansion initiated between 300,000 and 400,000 years ago, as was detected for each haplogroup. This pattern, which is congruent with other co-occurring Tridacna species, indicates a shared evolutionary history with expansion from past refuges following late-Pleistocene sea-level changes.
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First record of the Devil Clam, Tridacna mbalavuana Ladd 1934, in New Caledonia
Marine Biodiversity, 2016Co-Authors: Josina Tiavouane, Cécile FauvelotAbstract:The Devil Clam, Tridacna mbalavuana Ladd 1934, previously known as T. tevoroa Lucas, Ledua, Braley 1990, was described on the barrier reefs of Tonga and the Lau islands of Fiji. Here, we report two individuals found on the northeastern barrier reef of New Caledonia. While its known geographic range has expanded, its rarity and hence vulnerability persists.
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distribution of noah s giant clam Tridacna noae
Marine Biodiversity, 2015Co-Authors: Philippe Borsa, Cécile Fauvelot, Daphné Grulois, Josina Tiavouane, Colette C C Wabnitz, M Abdon R Naguit, Serge AndréfouëtAbstract:Previously confused with the small giant clam Tridacna maxima, the recently resurrected Noah’s giant clam, Tridacna noae, has been reported from the Taiwanese and the Ryukyu archipelagoes. Our recent underwater observations now extend its distribution to Dongsha (northern South China Sea), Bunaken (Sulawesi Sea), Madang and Kavieng (Bismarck Sea), the Alor archipelago (Sawu Sea), Kosrae (Caroline Islands), New Caledonia, the Loyalty Islands and Vanuatu (Coral Sea), Viti-Levu (Fiji), Wallis Island, and Kiritimati (Northern Line Islands). Published mitochondrial DNA sequences retrieved from open-access databases also indicate its presence in eastern Negros (Philippines), in the Molucca Sea, at Ningaloo Reef (Western Australia), and in the Solomon Islands. Noah’s giant clam is thus a widely distributed Indo-West Pacific species. Wherever research has been done on small giant clams throughout T. noae’s range, the inadvertent confusion of T. noae with T. maxima might have led to overestimating actual T. maxima densities and to errors in estimating demographic parameters.
Cheng-cheng Liu - One of the best experts on this subject based on the ideXlab platform.
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the first detection of the madden julian oscillation signal in daily to hourly resolution proxy records derived from a natural archive of giant clam shell Tridacna spp
Earth and Planetary Science Letters, 2021Co-Authors: Hong Yan, Haobai Fei, Cheng-cheng Liu, Nanyu Zhao, Pengchao Zhou, Fei Liu, Yuanjian Yang, Wei Yang, John DodsonAbstract:Abstract The Madden-Julian Oscillation (MJO) is the most prominent mode of intraseasonal variability in the tropics which is responsible for much of the observed intraseasonal climate variance not only there but also in higher latitudes. The short time-span of modern instrumental data limits our understanding of the MJO and obtaining MJO information from natural archives could extend this greatly. Here a Giant Clam shell (Tridacna spp.) with a life span about two years (from January 29, 2012 to December 9, 2013) was collected from the northern South China Sea, in the western Pacific. Several daily to hourly resolution biological and geochemical proxy records, including the daily growth rate, hourly Fe/Ca, Sr/Ca and fluorescence intensity, were developed to compare these with local weather/climate records. Spectral analyses suggested that these ultra-high resolution proxy records can clearly record MJO variability in the tropics. The substantial connection between the proxy records and MJO possibly linking through the local effective solar radiation, SST, precipitation and wind speeds. This is the first record of the MJO signal in a natural paleoclimate archive. Our findings provide new insights to study the MJO beyond the instrumental records, and since fossil Tridacna shells from different geological times can be used to investigate the MJO under various climate conditions.
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Dynamic of Tridacna spp. population variability in northern SCS over past 4500 years derived from AMS 14C dating
The Science of the total environment, 2020Co-Authors: Cheng-cheng Liu, Hong Yan, Haobai Fei, Ge Shi, Peng Cheng, Hanfeng Wen, Shugang Kang, Willie Soon, John DodsonAbstract:Abstract The marine bivalve, Tridacna spp. is an iconic invertebrate of the Indo-Pacific coral reef communities from Eocene to present. However, field observations found that the population of Tridacna spp. has declined in recent decades and some species are now endangered in the northern South China Sea (SCS) of western Pacific, which are speculated to be connected with the human overfishing and/or climate changes. Thus distinguishing the impacts of human activities and climate changes on Tridacna spp. populations is essential for understanding the dynamic of Tridacna spp. population variability. Such effort will be important in launching conservation policies and restoring population. Here, extensive sampling was applied on sub-fossil Tridacna spp. shells at the North Reef of the northern SCS, and the long-lived (with a lifespan more than 30 years) Tridacna spp. population index (LTPI) over the past 4500 years was obtained based on the AMS14C dating method. The results show that LTPI has experienced several short-term collapses (shorter than 200 years) over the past 4500 years, which may be associated with excessive cold winter temperatures. Remarkably, LTPI usually recovered rapidly after the rewarming of temperatures, indicating a robust self-recruitment mechanisms in response to natural climate changes. However, the last catastrophic collapse of LTPI that occurred at around ~1820 CE – ~1900 CE didn't rebound despite the significant rise in temperature over the recent 100 years. The decoupling between LTPI and climate changes in recent hundred years was probably induced by the increased commercial fishing in the SCS, which has overwhelmed and exacerbated the self-recruitment mechanisms between Tridacna spp. population and climate changes.
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A high-resolution δ18O record of modern Tridacna gigas bivalve and its paleoenvironmental implications
Palaeogeography Palaeoclimatology Palaeoecology, 2020Co-Authors: Hong Yan, Haobai Fei, Cheng-cheng Liu, Ge Shi, Enqing Huang, Yue Wang, Ergang Lian, Haowen DangAbstract:Abstract The lack of monthly-resolved paleoenvironmental records beyond the instrumental era hinders our full understanding of global climate dynamics. Tridacna gigas shells have a large potential to quantitatively document the variability of the ocean surface environment on time scales from daily to interannual in the past, while the applicability of the geochemical proxies of Tridacna gigas needs to be quantitively investigated. Here we establish a chronology for a Tridacna gigas shell from the southern South China Sea (SCS) by identifying daily growth laminae using a laser scanning confocal microscope (LSCM). Our high-resolution Tridacna gigas shell δ18Oshell record throughout 1989–2013 shows a high correlation with changes in local precipitation and the index of El Nino-Southern Oscillations (ENSO) on the interannual time scale. Together with observed sea surface temperature (SST), we calculated seawater δ18O (δ18Osw) and derived sea surface salinity (SSS) change in the southern SCS based on the Tridacna gigas shell δ18O record. Our salinity-budget calculation results suggest that the SSS variability in the southern SCS is predominantly affected by the vertical mixing and sea surface freshwater flux. Our study reveals that the Tridacna gigas shell is an ideal archive for high-resolution and quantitative paleoenvironmental reconstructions in tropical ocean regions, thus providing a new window to explore paleoenvironmental changes on annual and interannual time scales.
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temperature seasonality and enso variability in the northern south china sea during the medieval climate anomaly interval derived from the sr ca ratios of Tridacna shell
Journal of Asian Earth Sciences, 2019Co-Authors: Cheng-cheng Liu, Hong Yan, Haobai Fei, Ge Shi, Willie Soon, John Dodson, Wenchao ZhangAbstract:Abstract The nature of how the El Nino–Southern Oscillation (ENSO) and its seasonality respond to warmer climate is critical knowledge to predict future climates under the expected anthropogenic warming scenario. In this study, a sub-fossil Tridacna gigas specimen was collected from the northern SCS and AMS14C dating suggested that the animal lived around AD 1099, during the Medieval Climate Anomaly (MCA) interval, the most recent natural warm period of the late Holocene. Monthly Sr/Ca ratios were determined by the ICP-OES measurements and a 30-year long SST record was calculated based on a Sr/Ca-SST calibration equation. The results showed that the SST seasonality for this 30-year window around AD 1099 was about 3.11 °C, which is smaller than the modern warm period (i.e., about 4.36 °C for AD 1994 ∼ 2005 interval). This new result is consistent with another published Tridacna gigas record that was dated around AD 990 from the northern SCS. The signals of ENSO activity were also extracted from the reconstructed SST record and statistical analyses yielded 9 El Nino events and 8 La Nina events within the 30-year record, indicating that the frequency of ENSO activity around AD 1099 was similar to the modern instrumental period.
Li-lian Liu - One of the best experts on this subject based on the ideXlab platform.
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Historical divergences associated with intermittent land bridges overshadow isolation by larval dispersal in co‐distributed species of Tridacna giant clams
Journal of Biogeography, 2018Co-Authors: Jude Keyse, Li-lian Liu, Thomas Huelsken, Eric A Treml, Timery S. Deboer, Paul H. Barber, Marc Kochzius, Agus Nuryanto, Jonathan P. A. Gardner, Shane PennyAbstract:Aim: The aim of this study was to test historical and contemporary influences on population structure in the giant clams, Tridacna maxima (Roding, 1798) and T. crocea (Lamarck, 1819). To refine the location of clade boundaries within a newly resurrected species, Tridacna noae (Roding, 1798). Location: Indo-Australian archipelago, including Indonesia, the Philippines, Australia, Papua New Guinea, the Solomon Islands, Republic of Kiribati, the Line Islands and Taiwan. Methods: We used isolation-migration (IMa) coalescent models and distance-based redundancy analyses (dbRDA) to test the relative influence of barriers and continuous distances on historical divergence, gene flow and population structure of T. maxima and T. crocea. Continuous metrics of distance included present-day and Last Glacial Maximum overwater distances along with probability of larval dispersal (LD) among sampling sites. We combined new mitochondrial cytochrome oxidase subunit I (mtDNA COI) sequences with existing data to compile the largest data set of these species yet analysed. Results: The Pleistocene land barriers of the Sunda Shelf and Torres Strait were associated with old (>0.5 Myr) divergence times. The western and eastern boundaries of the Halmahera Eddy were also locations of significant, but more recent, divergence. No gene flow was detected across any of the four barriers tested. Larval dispersal distances between sampling sites were significant predictors of T. crocea population structure, accounting for differentiation above and beyond the contribution of barriers. We further delineated the species range of T. noae and showed that its two known clades are sympatric in central Indonesia. Main conclusions: The strong signature of historical barriers on genetic differentiation argues against the assumption that Indo-Pacific Tridacna are open meta-populations. Despite similar life histories, T. maxima and T. crocea differ in their mtDNA population structure. The widespread species (T. maxima) exhibits population structure linked solely with historical factors, whereas T. crocea's population structure reflects both historical factors and LD distances.
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Thriving populations with low genetic diversity in giant clam species, Tridacna maxima and Tridacna noae, at Dongsha Atoll, South China Sea
Regional Studies in Marine Science, 2018Co-Authors: Mei Lin Neo, Li-lian Liu, Danwei Huang, Keryea SoongAbstract:Abstract Giant clams provide valuable functions to the coral reefs and traditional fisheries in the South China Sea (SCS), but many populations face escalating threats of overexploitation and habitat loss. To provide critical biodiversity data for development of protection and sustainable utilisation strategies, we examine the status of wild tridacnine population at Dongsha Atoll, the largest northernmost atoll of the SCS. This study also examines the genetic patterns of Tridacna maxima and Tridacna noae, based on partial mitochondrial COI gene sequences. We found four species at Dongsha Atoll with an overall density of 3.14 per 100 m2. Over-harvesting may have depleted populations of T. squamosa and Hippopus hippopus, and they may no longer be reproductively viable. Populations of T. maxima and T. noae appear to be thriving and replenished by recruits, but species showed low levels of mitochondrial genetic diversity that could reduce its adaptability and may become further impacted by exploitation and global warming. Haplotype networks for T. maxima and T. noae showed strong significant population structuring consistent with contemporary geographic boundaries: Dongsha Atoll, Taiwan and Philippines—likely established by the intrusion of the Kuroshio Current. Given the contrasting species status and genetic diversity, conservation strategies need to be tailored to increase success of these efforts.
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On the validity of Noah’s giant clam Tridacna noae (Röding, 1798) and its synonymy with Ningaloo giant clam Tridacna ningaloo Penny & Willan, 2014
Raffles Bulletin of Zoology, 2015Co-Authors: Philippe Borsa, Serge Andréfouët, Cécile Fauvelot, Tsun-thai Chai, Hirofumi Kubo, Li-lian LiuAbstract:A new giant clam species, Tridacna ningaloo Penny & Willan, 2014 has been described from Ningaloo Reef, Western Australia. Meanwhile, it has been suggested that Noah's giant clam, Tridacna noae (Röding, 1798), previously resurrected from synonymy with T. maxima (Röding, 1798), is an invalid name. We assessed the validity of resurrecting T. noae and designating a neotype for it against the rules of zoological nomenclature and found no flaw in these acts. We then compared the genetic and morphological characters used in the respective diagnoses of T. noae and the newly-described Tridacna ningaloo. No difference was apparent between T. ningaloo and T. noae except, possibly, in mantle ornamentation patterns. In particular, the holotype of T. ningaloo possesses a mitochondrial DNA haplotype identical to T. noae. Thus, the hypothesis that T. ningaloo is a species distinct from T. noae was not supported by clear morphological evidence and it was contradicted by the available genetic evidence. Tridacna ningaloo should be regarded as a junior synonym of T. noae.
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On the validity of Noah's giant clam Tridacna noae (Roding, 1798) and its synonymy with Ningaloo giant clam Tridacna ningaloo Penny & Willan, 2014
Raffles Bulletin of Zoology, 2015Co-Authors: Philippe Borsa, Serge Andréfouët, Cécile Fauvelot, Tsun-thai Chai, Hirofumi Kubo, Li-lian LiuAbstract:A new giant clam species, Tridacna ningaloo Penny & Willan, 2014 has been described from Ningaloo Reef, Western Australia. Meanwhile, it has been suggested that Noah's giant clam, Tridacna noae (Roding, 1798), previously resurrected from synonymy with T. maxima (Roding, 1798), is an invalid name. We assessed the validity of resurrecting T. noae and designating a neotype for it against the rules of zoological nomenclature and found no flaw in these acts. We then compared the genetic and morphological characters used in the respective diagnoses of T. noae and the newly-described Tridacna ningaloo. No difference was apparent between T. ningaloo and T. noae except, possibly, in mantle ornamentation patterns. In particular, the holotype of T. ningaloo possesses a mitochondrial DNA haplotype identical to T. noae. Thus, the hypothesis that T. ningaloo is a species distinct from T. noae was not supported by clear morphological evidence and it was contradicted by the available genetic evidence. Tridacna ningaloo should be regarded as a junior synonym of T. noae.
