DOI： https://doi.org/10.3755/galaxea.G27O-5

Publishing type：Research paper (scientific journal)  

DOI： 10.1111/2041-210X.70046

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Publishing type：Research paper (scientific journal)   Publisher：Inter-Research Science Center  

Changes in the distribution range and timing of life events in fish in response to warming oceans have been reported in several marine ecosystems. However, few studies have demonstrated the impact of increasing temperature on the individual growth and thermal trajectories of fish. We examined the growth and temperature trajectories of juvenile Japanese jack mackerel Trachurus japonicus in the western waters off Kyushu, Japan, based on growth increments and high-resolution isotopic analyses of archived otoliths between the 1960s-1970s and 2000s-2010s. T. japonicus juveniles in the 2000s-2010s hatched from February to April, whereas juvenile hatching in the 1960s-1970s ranged from March to May, corresponding to earlier spawning in recent decades. The otolith radius from the nucleus to specific dates represents the somatic growth trajectory of the fish: this distance was larger from April to August in the 2000s-2010s than that in the 1960s-1970s, indicating that earlier hatching in the 2000s-2010s resulted in a larger body size throughout life than in the 1960s-1970s. The trajectories of the oxygen stable isotope ratios in otoliths showed that the temperatures experienced by the fish from spring to summer were comparable between the study periods. Our results suggest that warming during late winter in recent decades has resulted in earlier spawning and occurrence of T. japonicus juveniles, resulting in the fish experiencing comparable thermal conditions between the 2 study periods. The phenological shift in spawning seemed to be recorded in individual growth and the temperature trajectories in the otoliths of T. japonicus.

DOI： 10.3354/meps14557

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Publishing type：Research paper (scientific journal)  

DOI： 10.3389/fmars.2024.1392102

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Authorship：Lead author,　Corresponding author   Language：Japanese   Publisher：南国 : 日本サンゴ礁学会  

DOI： https://doi.org/10.3755/jcrs.26.19

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Publisher：Frontiers Media SA  

<jats:sec><jats:title>Introduction</jats:title><jats:p>Small pelagic fishes constitute large proportions of fisheries and are important components linking lower and higher trophic levels in marine ecosystems. Many small pelagic fishes in the Northwest Pacific spawn upstream in the Kuroshio and spend their juvenile stage in the Kuroshio Front area, indicating that the Kuroshio Current system impacts their stock fluctuations. However, the distribution of these fish relative to the Kuroshio has not been determined due to dynamic spatio-temporal fluctuations of the system. Here, the recent development of environmental DNA (eDNA) monitoring enabled us to investigate the distribution patterns of four economically important small pelagic fishes (Japanese sardine <jats:italic>Sardinops melanostictus</jats:italic>, Japanese anchovy <jats:italic>Engraulis japonicus</jats:italic>, chub mackerel Scomber japonicus, and blue mackerel <jats:italic>Scomber australasicus</jats:italic>) in the Kuroshio Current system. </jats:p></jats:sec><jats:sec><jats:title>Methods</jats:title><jats:p>The influence of environmental factors, such as sea water temperature, salinity, oxygen concentration, chlorophyll-a concentration, and prey fish on the occurrence and quantity of target fish eDNA was analyzed using generalized additive models. In addition, the detection (presence) of target fish eDNA were compared between the offshore and inshore side areas of the Kuroshio axis.</jats:p></jats:sec><jats:sec><jats:title>Results</jats:title><jats:p>Sea water temperature showed important effect, especially on the distribution of Japanese sardine and Japanese anchovy, whereas the distribution pattern of chub mackerel and blue mackerel was greatly influenced by the eDNA quantity of Japanese sardine and Japanese anchovy (especially potential prey fish: Japanese anchovy). In addition, we found that the four target fish species could be observed in areas on the inshore side or around the Kuroshio axis, while they were hardly found on the offshore side.</jats:p></jats:sec><jats:sec><jats:title>Conclusion</jats:title><jats:p>Based on eDNA data, we succeeded in revealing detailed spatial distribution patterns of small pelagic fishes in the Kuroshio Current system and hypothesized predator–prey relationships influence their distribution in small pelagic fish communities.</jats:p></jats:sec>

DOI： 10.3389/fmars.2023.1121088

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Publisher：Elsevier BV  

DOI： 10.1016/j.scitotenv.2023.162293

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Publisher：Frontiers Media SA  

<jats:p>Reconstruction of water temperatures experienced by marine fishes using otolith oxygen stable isotopes (<jats:italic>δ</jats:italic><jats:sup>18</jats:sup>O) as natural thermometers has been proven to be a useful approach for estimating migration routes or movement patterns. This method is based on the mechanism that the equilibrium fractionation of <jats:italic>δ</jats:italic><jats:sup>18</jats:sup>O<jats:italic><jats:sub>otolith</jats:sub></jats:italic> against ambient water exhibits a species-specific thermal sensitivity during the process of otolith aragonitic CaCO<jats:sub>3</jats:sub> precipitation. In this study, a laboratory-controlled rearing experiment was conducted to determine the temperature dependency of <jats:italic>δ</jats:italic><jats:sup>18</jats:sup>O fractionation on the anadromous fish species, chum salmon (<jats:italic>Oncorhynchus keta</jats:italic>), of which the detailed migration routes have not been elucidated yet. To test that temperature was the only factor affecting <jats:italic>δ</jats:italic><jats:sup>18</jats:sup>O<jats:italic><jats:sub>otolith</jats:sub></jats:italic> fractionation, this study ensured a relatively stable rearing condition, evaluated the isotope composition of the rearing water, and analyzed carbon isotope (<jats:italic>δ</jats:italic><jats:sup>13</jats:sup>C<jats:italic><jats:sub>otolith</jats:sub></jats:italic>) to examine the potential effect of kinetic and metabolic isotopic fractionations. The <jats:italic>δ</jats:italic><jats:sup>18</jats:sup>O<jats:italic><jats:sub>otolith</jats:sub></jats:italic> fractionation equation on chum salmon was thereby determined within a temperature range of 9–20°C and was indistinguishable from the equation of synthetic aragonite; The <jats:italic>δ</jats:italic><jats:sup>13</jats:sup>C<jats:italic><jats:sub>otolith</jats:sub></jats:italic> was affected by both physiological processes and <jats:italic>δ</jats:italic><jats:sup>13</jats:sup>C<jats:italic><jats:sub>DIC</jats:sub></jats:italic>; In lower temperatures settings, both oxygen and carbon isotopes depleted simultaneously. This study suggests that the chum salmon species-specific oxygen isotope fractionation equation could be used on reconstruction of temperature history and also throw insights into understanding the incorporation of oxygen and carbon sources during calcification process for otoliths.</jats:p>

DOI： 10.3389/fmars.2022.1072068

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Publisher：Frontiers Media SA  

<jats:p>Algal symbionts of corals can influence host stress resistance; for example, in the Pacific Ocean, whereas <jats:italic>Cladocopium</jats:italic> (C-type) is generally dominant in corals, <jats:italic>Durusdinium</jats:italic> (D-type) is found in more heat-resistant corals. Thus, the presence of D-type symbiont likely increases coral heat tolerance, and this symbiotic relationship potentially provides a hint to increase the stress tolerance of coral–algal symbioses. In this study, transcriptome profiles of <jats:italic>Cladocopium-</jats:italic> and <jats:italic>Durusdinium</jats:italic>-harboring <jats:italic>Acropora solitaryensis</jats:italic> (C-coral and D-coral, respectively) and algal photosystem functioning (<jats:italic>F</jats:italic><jats:sub><jats:italic>v</jats:italic></jats:sub><jats:italic>/F</jats:italic><jats:sub><jats:italic>m</jats:italic></jats:sub>) under bleaching conditions (high temperature and light stress) were compared. Stress treatment caused algal photoinhibition that the <jats:italic>F</jats:italic><jats:sub><jats:italic>v</jats:italic></jats:sub>/<jats:italic>F</jats:italic><jats:sub><jats:italic>m</jats:italic></jats:sub> value of Symbiodiniaceae was immediately reduced. The transcriptome analysis of corals revealed that genes involved in the following processes were detected: endoplasmic reticulum (ER) stress, mitophagy, apoptosis, endocytosis, metabolic processes (acetyl-CoA, chitin metabolic processes, etc.), and the PI3K-AKT pathway were upregulated, while DNA replication and the calcium signaling pathway were downregulated in both C- and D-corals. These results suggest that unrepaired DNA and protein damages were accumulated in corals under high temperature and light stress. Additionally, some differentially expressed genes (DEGs) were specific to C- or D-corals, which includes genes involved in transient receptor potential (TRP) channels and vitamin B metabolic processes. Algal transcriptome analysis showed the increased expression of gene encoding photosystem and molecular chaperone especially in D-type symbiont. The transcriptome data imply a possible difference in the stress reactions on C-type and D-type symbionts. The results reveal the basic process of coral heat/light stress response and symbiont-type-specific coral transcriptional responses, which provides a perspective on the mechanisms that cause differences in coral stress tolerance.</jats:p>

DOI： 10.3389/fphys.2022.806171

PubMed

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Language：English   Publisher：GEOCHEMICAL SOCIETY OF JAPAN  

<p>To understand seawater properties, such as water mass structure and mixing, geochemical analyses are useful. However, geochemical datasets for seawater that fully cover coastal areas of Hokkaido, North Japan are lacking. Here we report comprehensive geochemical analyses of seawater (salinity, δ¹⁸O, δD, and Δ¹⁴C) collected in August–September 2021 from coastal areas of Hokkaido as well as the west coast of Tohoku (Northeast Japan). These datasets are expected to improve our understanding of seawater properties around Hokkaido, thereby contributing to oceanography, climatology, biogeochemical cycles, and fishery science.</p>

DOI： 10.2343/geochemj.gj22021

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Publisher：Frontiers Media SA  

<jats:p>Numerous genes involved in calcification, algal endosymbiosis, and the stress response have been identified in corals by large-scale gene expression analysis, but functional analysis of those genes is lacking. There are few experimental examples of gene expression manipulation in corals, such as gene knockdown by RNA interference (RNAi). The purpose of this study is to establish an RNAi method for coral juveniles. As a first trial, the genes encoding green fluorescent protein (GFP, an endogenous fluorophore expressed by corals) and thioredoxin (TRX, a stress response gene) were selected for knockdown. Synthesized double-stranded RNAs (dsRNAs) corresponding to GFP and TRX were transformed into planula larvae by lipofection method to attempt RNAi. Real-time PCR analysis to verify knockdown showed that GFP and TRX expression levels tended to decrease with each dsRNA treatment (not significant). In addition, stress exposure experiments following RNAi treatment revealed that planulae with TRX knockdown exhibited increased mortality at elevated temperatures. In GFP-knockdown corals, decreased GFP fluorescence was observed. However, the effect of GFP-knockdown was confirmed only in the coral at the initial stages of larval metamorphosis into polyps, but not in planulae and 1 month-old budding polyps. This study showed that lipofection RNAi can be applied to coral planulae and polyps after settlement, and that this method provides a useful tool to modify expression of genes involved in stress tolerance and fluorescence emission of the corals.</jats:p>

DOI： 10.3389/fmars.2021.688876

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Publisher：Elsevier BV  

The Yesso scallop, Patinopecten yessoensis (Jay), is one of the most important bivalve species in the Japanese and Chinese mariculture industry. In recent years, however, high incidences of scallop shell deformity and mortality have occurred with increasing frequency, but timing of onset and underlying causes are often unclear. Here, we proposed a promising δ

DOI： 10.1016/j.marenvres.2020.105149

PubMed

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Publisher：Wiley  

<jats:title>Summary</jats:title><jats:p>Although sulfate ions are the main form of sulfur in the ocean, there is limited knowledge on their use by living organisms. Stable isotope labelling and NanoSIMS analysis were used in this study to clarify how sulfate, in seawater, is assimilated by corals and zooxanthellae at the cellular level. Aposymbiotic and symbiotic coral juveniles from the genus <jats:italic>Acropora</jats:italic> were incubated for 2 days in filtered seawater with <jats:sup>34</jats:sup>S‐labelled sulfate. Further, the labelled corals were incubated for additional 2 days in natural seawater. Mapping of sulfur isotopes (<jats:sup>34</jats:sup>S/<jats:sup>32</jats:sup>S) showed that the ‘hotspots’ were enriched in <jats:sup>34</jats:sup>S on a sub‐micro level and were heterogeneously distributed in the coral soft tissues. Specifically, <jats:sup>34</jats:sup>S hotspots were found in both the symbiotic zooxanthellae and coral host tissues. In aposymbiotic corals, <jats:sup>34</jats:sup>S was detected in the tissues, indicating that the host corals directly assimilated the sulfate ions without any aid from the zooxanthellae. Even after 2 days in normal seawater, the <jats:sup>34</jats:sup>S label was clearly seen in both symbiotic and aposymbiotic corals, indicating that the assimilated sulfur was retained for at least 2 days.</jats:p>

DOI： 10.1111/1758-2229.12908

PubMed

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Publisher：Elsevier BV  

Abstract Ocean acidification can negatively impact marine bivalves, especially their shell mineralization processes. Consequently, whether marine bivalves can rapidly acclimate and eventually adapt in an acidifying ocean is now increasingly receiving considerable attention. Projecting the fate of this vulnerable taxonomic group is also pivotal for the science of sclerochronology – the study which seeks to deduce records of past environmental changes and organismal life-history traits from various geochemical properties of periodically layered hard tissues (bivalve shells, corals, fish otoliths, etc.). In this review, we provide a concise overview of the long-term and transgenerational responses of marine bivalves to elevated pCO2 manifested at different levels of biological organization, with a specific focus on responses of geochemical properties (stable carbon and oxygen isotopes, minor and trace elements and microstructures) of their shells. Without exception, positive transgenerational responses to an elevated pCO2 scenario projected for the year 2100 have been found in all five bivalve species hitherto studied, under the umbrella of two non-genetic mechanisms (increased maternal provisioning and epigenetic inheritance), suggesting that marine bivalves have remarkable transgenerational phenotypic plasticity which allows them to respond plastically and acclimate rapidly in an acidifying ocean. Rapid transgenerational acclimation, especially in terms of physiological processes, however, hinders a reliable interpretation of proxy records. Transgenerationally acclimated bivalves can actively modify the calcification physiology in response to elevated pCO2, which in turn affects the processes of almost all geochemical proxies preserved in their shells. In particular, stable carbon isotopes, metabolically regulated elements (Na, K, Cu, Zn, Fe, etc.), and shell microstructures can be highly biased. In this context, we propose a number of challenges and opportunities the field of sclerochronology may face.

DOI： 10.1016/j.ecss.2020.106620

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Publisher：Elsevier BV  

Abstract To determine the temperature history of early life stages of chub mackerel (Scomber japonicus), otolith stable oxygen isotope ratios (δ18Ootolith) of larval and juvenile fish collected in the Kuroshio–Oyashio transition area during 2004–2015 were analyzed, and experienced temperatures were estimated accordingly. The δ18Ootolith values decreased with otolith growth during the larval stage, whereas those for juveniles were positively correlated with otolith radius and increased with increasing otolith size. Combinations of δ18Ootolith values, average otolith daily increment width, and daily age were representative of the differences between better and poorer recruitment years, the former being characterized by earlier spawning and faster growth (resulting from cooler experienced temperatures), and the latter by slower growth. Analyzed fish were sorted into larval and early juvenile growth stages by cluster analysis; the high-growth cluster exhibited higher δ18Ootolith values than the low-growth cluster. The conversion of δ18Ootolith values to water temperature indicated that the higher growth cluster experienced a water temperature ca. 2.0 °C cooler during the later juvenile stage. Therefore, our results suggest the presence of a growth positive spiral, wherein individuals with high initial growth proactively enter cooler water temperature areas, accessing a highly nutritious diet resulting in further rapid growth.

DOI： 10.1016/j.dsr2.2019.104660

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Publisher：Elsevier BV  

Abstract Stable carbon isotope ratios (δ13C) of mussel soft tissues have been widely used to characterize baseline δ13C isoscapes and identify carbon sources at the base of coastal food webs. Extending soft tissue δ13C records back in time, however, is extremely challenging due to very limited sample availability. Here, we test if the stable carbon isotopic composition of periostracum (the outermost organic layer of the shell) in the Mediterranean mussel (Mytilus galloprovincialis) can be used as an environmental archive, similar to soft tissue records. In general, spatial and seasonal variations of periostracum δ13C values are comparable to those of soft tissues, but apparently the latter are more time-averaged and smoothed. Irrespective of such offset, there is a significant linear correlation between mussel periostracum and soft tissue δ13C values (R2 = 0.608, p

DOI： 10.1016/j.gca.2019.06.038

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Language：English  

DOI： 10.7717/peerj.7241

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Publisher：Elsevier BV  

Sea surface salinity (SSS) is a key parameter to understand and predict many physical, chemical and biological processes in dynamic coastal environments. Yet, in many regions, instrumental measurements are spatially sparse and insufficiently long, hindering our ability to document changes, causes, and consequences of SSS across different time scales. Therefore, there is an need to develop a robust proxy to extend SSS records back in time. Here, we test whether SSS can be reconstructed reliably and quantitatively from shell oxygen isotopic ratios (δ

DOI： 10.1016/j.scitotenv.2019.03.405

PubMed

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Publisher：Wiley  

<jats:title>Abstract</jats:title><jats:p>
<jats:list>

<jats:list-item><jats:p>Tracking the movement of migratory fish is of great importance for efficient conservation, although this has been technically difficult to achieve in small fish to which artificial tags cannot be attached.</jats:p></jats:list-item>

<jats:list-item><jats:p>We show that migration history can be reproduced by combining high‐resolution otolith stable oxygen isotope ratio (δ<jats:sup>18</jats:sup>O) analysis and numerical simulation.</jats:p></jats:list-item>

<jats:list-item><jats:p>High‐precision micromilling and microvolume carbonate analysing systems had the remarkable capability of extracting the otolith δ<jats:sup>18</jats:sup>O profiles with 10–30 days resolution. Furthermore, reasonable movements were reproduced by searching the routes consistent with the otolith δ<jats:sup>18</jats:sup>O profile, using an individual‐based model with random swimming behaviour.</jats:p></jats:list-item>

<jats:list-item><jats:p>This method will be a valuable alternative to tagging and electronic loggers for revealing migration routes in early life stages, thereby providing crucial information to understand population structures and the environmental cause of recruitment variabilities, and to validate and improve fish movement models.</jats:p></jats:list-item>
</jats:list>
</jats:p>

DOI： 10.1111/2041-210x.13098

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Language：English   Publisher：[Tokyo] : [Springer Nature Japan]  

To investigate the population dynamics of naturally recruited wild Japanese eels, fisheries data of wild individuals in Okayama Prefecture were investigated as a case study. Wild and stocked eels were discriminated using a recently developed method based on otolith stable isotopes. Of the 161 eels captured in freshwater areas where eels had been stocked, 98.1% were discriminated as stocked. In contrast, 82.8% of 128 eels captured in coastal areas where eels are not stocked were discriminated as wild. There was a significant decrease in longline and set-net catch per unit effort between 2003 and 2016 in the coastal areas where most eels were discriminated as wild, indicating ongoing depletion of wild Japanese eels in these waters.

DOI： 10.1007/s12562-018-1225-2

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Publisher：Springer Singapore  

DOI： 10.1007/978-981-10-6473-9_3

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Language：English   Publisher：International Coastal Research Center, Atmosphere and Ocean Research Institute, the University of Tokyo  

DOI： 10.15083/00076337

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Language：Japanese   Publisher：The Oceanographic Society of Japan  

<p>Various studies have been conducted to elucidate the climate variability impacts on living marine resources. Larval and juvenile stages are critical periods for the recruitment of living marine resources. However, limitations of observation methods for directly investigating the environments that larvae and juveniles experienced have been obstacles to our understanding. We reviewed the previous studies on climate variability impacts on living marine resources and discussed how reconstruction of environmental histories of larvae and juveniles is important for our understanding of climate variability impacts on living marine resources. We proposed a new, integrated method to reconstruct environmental histories of larvae and juveniles using otolith oxygen stable isotope analyses and fish growth–migration models. Together with the growth estimated from otolith daily increments, it is possible to elucidate climate impacts on larval and juvenile growth through environmental histories of larvae and juveniles using their realistic migration routes.</p>

DOI： 10.5928/kaiyou.27.1_59

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Language：English  

DOI： 10.1130/g39516.1

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Publisher：Elsevier BV  

Abstract We evaluated the use of the stable oxygen isotope (δ 18 O) in the otolith as a proxy for the temperature history of Japanese sardine Sardinops melanostictus individuals. Japanese sardine juveniles were reared in three different water temperatures over the course of a month. Otolith δ 18 O ( δ otolith ) was analyzed by extracting the portions formed during the rearing period using a micromill. δ 18 O of the rearing water ( δ water ) was also analyzed. A linear relationship between otolith δ 18 O and ambient water temperature was identified as follows: δ otolith  −  δ water  = −0.18 *  T  + 2.69 (r 2  = 0.91, p  Sardinops spp., with resulting application to wild Japanese sardine captured in the Pacific Ocean showing that it estimates a more realistic in situ temperature. Our findings suggest that the Japanese sardine-specific isotopic fractionation equation should be used when interpreting otolith δ 18 O of the Japanese sardine, and the methods presented here could also be useful to understand the temperature history of other fish species.

DOI： 10.1016/j.fishres.2017.05.004

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Publisher：The Company of Biologists  

<jats:title>ABSTRACT</jats:title><jats:p>Sulfur-containing compounds are important components of all organisms, but few studies have explored sulfate utilization in corals. Our previous study found that the expression of a sulfur transporter (SLC26A11) was upregulated in the presence of Symbiodinium cells in juveniles of the reef-building coral Acropora tenuis. In this study, we performed autoradiography using 35S-labeled sulfate ions (35SO4 2−) to examine the localization and amount of incorporated radioactive sulfate in the coral tissues and symbiotic algae. Incorporated 35SO4 2− was detected in symbiotic algal cells, nematocysts, ectodermal cells and calicoblast cells. The combined results of 35S autoradiography and Alcian Blue staining showed that incorporated 35S accumulated as sulfated glycosaminoglycans (GAGs) in the ectodermal cell layer. We also compared the relative incorporation of 35SO4 2− into coral tissues and endosymbiotic algae, and their chemical fractions in dark versus light (photosynthetic) conditions. The amount of sulfur compounds, such as GAGs and lipids, generated from 35SO4 2− was higher under photosynthetic conditions. Together with the upregulation of sulfate transporters by symbiosis, our results suggest that photosynthesis of algal endosymbionts contributes to the synthesis and utilization of sulfur compounds in corals.</jats:p>

DOI： 10.1242/bio.020164

PubMed

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Publisher：Springer Science and Business Media LLC  

<jats:title>Abstract</jats:title><jats:p>The distribution of corals in Japan covers a wide range of latitudes, encompassing tropical to temperate zones. However, coral communities in temperate zones contain only a small subset of species. Among the parameters that determine the distribution of corals, temperature plays an important role. We tested the resilience to cold stress of three coral species belonging to the genus <jats:italic>Acropora</jats:italic> in incubation experiments. <jats:italic>Acropora pruinosa</jats:italic>, which is the northernmost of the three species, bleached at 13 °C, but recovered once temperatures were increased. The two other species, <jats:italic>A</jats:italic>. <jats:italic>hyacinthus</jats:italic> and <jats:italic>A</jats:italic>. <jats:italic>solitaryensis</jats:italic>, which has a more southerly range than <jats:italic>A</jats:italic>. <jats:italic>pruinosa</jats:italic>, died rapidly after bleaching at 13 °C. The physiological effects of cold bleaching on the corals included decreased rates of photosynthesis, respiration and calcification, similar to the physiological effects observed with bleaching due to high temperature stress. Contrasting hot bleaching, no increases in antioxidant enzyme activities were observed, suggesting that reactive oxygen species play a less important role in bleaching under cold stress. These results confirmed the importance of resilience to cold stress in determining the distribution and northern limits of coral species, as cold events causing coral bleaching and high mortality occur regularly in temperate zones.</jats:p>

DOI： 10.1038/srep18467

PubMed

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Publisher：Elsevier BV  

Abstract The frequency and severity of coral bleaching events have increased in recent decades. Regionally, human-attributed nutrient pollution, particularly nitrate, has increased in coastal areas due to inflow from rivers and groundwater. The combined effects of increased nitrate concentrations with high temperature or high light on bleaching events and reactive oxygen species levels (ROS) were tested. Coral fragments of Montipora digitata were incubated for 3 and 6 days at different light intensities (200 and 600 μmol m −2  s −1 ), temperatures (27 and 32 °C), and nitrate concentrations (

DOI： 10.1016/j.rsma.2015.08.012

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Publisher：Public Library of Science (PLoS)  

Reef-building corals switch endosymbiotic algae of the genus Symbiodinium during their early growth stages and during bleaching events. Clade C Symbiodinium algae are dominant in corals, although other clades - including A and D - have also been commonly detected in juvenile Acroporid corals. Previous studies have been reported that only molecular data of Symbiodinium clade were identified within field corals. In this study, we inoculated aposymbiotic juvenile polyps with cultures of clades C1 and D Symbiodinium algae, and investigated the different effect of these two clades of Symbiodinium on juvenile polyps. Our results showed that clade C1 algae did not grow, while clade D algae grew rapidly during the first 2 months after inoculation. Polyps associated with clade C1 algae exhibited bright green fluorescence across the body and tentacles after inoculation. The growth rate of polyp skeletons was lower in polyps associated with clade C1 algae than those associated with clade D algae. On the other hand, antioxidant activity (catalase) of corals was not significantly different between corals with clade C1 and clade D algae. Our results suggested that clade D Symbiodinium algae easily form symbiotic relationships with corals and that these algae could contribute to coral growth in early symbiosis stages.

DOI： 10.1371/journal.pone.0098999

PubMed

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Publisher：Public Library of Science (PLoS)  

Modern scleractinian coral skeletons are commonly composed of aragonite, the orthorhombic form of CaCO3. Under certain conditions, modern corals produce calcite as a secondary precipitate to fill pore space. However, coral construction of primary skeletons from calcite has yet to be demonstrated. We report a calcitic primary skeleton produced by the modern scleractinian coral Acropora tenuis. When uncalcified juveniles were incubated from the larval stage in seawater with low mMg/Ca levels, the juveniles constructed calcitic crystals in parts of the primary skeleton such as the septa; the deposits were observable under Raman microscopy. Using scanning electron microscopy, we observed different crystal morphologies of aragonite and calcite in a single juvenile skeleton. Quantitative analysis using X-ray diffraction showed that the majority of the skeleton was composed of aragonite even though we had exposed the juveniles to manipulated seawater before their initial crystal nucleation and growth processes. Our results indicate that the modern scleractinian coral Acropora mainly produces aragonite skeletons in both aragonite and calcite seas, but also has the ability to use calcite for part of its skeletal growth when incubated in calcite seas.

DOI： 10.1371/journal.pone.0091021

PubMed

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Language：English  

The coral species, Montipora digitata and seagrass, Thalassia hemprichii, co-inhabit the southern portion of the reef moat in Bise, Okinawa, Japan. To elucidate the biogeochemical relationship between coral and seagrass in mixed communities of the coral reef ecosystem, the carbon metabolisms and the inorganic nitrogen flux rates were estimated in various reef habitats. We used benthic chambers to investigate sandy, seagrass, coral-seagrass mixed communities, coral, and acorn worm habitats. Relatively high concentrations of nitrate and nitrite ions (NO_x) were observed in all habitats due to coastal groundwater inflow. The uptake rate constant of NO_x was the highest in the coral-seagrass habitat and was significantly different from the rate constant in the seagrass habitat, indicating that seagrass benefits from co-inhabitation with coral. Dissolution of CaCO_3 was observed in the seagrass and coral-seagrass communities. This decline in basal coral carbonate substrate may contribute to increased fragmentation and dispersal of the coral habitat. On a biogeochemical scale, the coral-seagrass relationship benefits the seagrass in terms of NO_x availability and benefits the coral in terms of carbonate dissolution, increasing fragmentation, and furthering habitat development.

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Language：Japanese   Publisher：The Japanese Coral Reef Society  

Over the past several decades, coral reef ecosystems have experienced various stresses and extensive degradation due to increased anthropogenic activity. Reef-building corals respond to stress in various ways, including bleaching. Corals exhibit defense mechanisms against stress, although many of these functions have not yet been clarified. Understanding the defense mechanisms in corals could provide important information for finding solutions to stress-related responses such as coral bleaching. The entire coral genome has recently been sequenced and this is expected to lead to breakthroughs in research on coral defense mechanisms. In this review, we describe coral bleaching, oxidative stress, antioxidants, mycosporine-like amino acids, and fluorescent proteins as responses and defense mechanisms against environmental stressors such as high temperature, strong irradiance, and ultraviolet radiation, from the perspectives of molecular biology, physiology, and ecology.

DOI： 10.3755/jcrs.16.47

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Language：English   Publisher：日本サンゴ礁学会  

DOI： 10.3755/jcrs.16.1

CiNii Research

Language：Japanese   Publisher：The Society of Eco-Engineering  

The coexistence of seagrasses and corals at Bise, Okinawa, Japan, was investigated in terms of nutrient dynamics, dissolved organic carbon (DOC), and microbial abundance. Four incubation conditions (seawater, seagrass, coral, and seagrass with coral [sg+cr]) were examined using in situ incubation methods. ¹³C was used as a tracer to evaluate primary production in the water column and carbon fixation in seagrass and coral tissues. Primary production was higher in the water column in seagrass incubations, resulting in increased dissolved oxygen (DO) concentrations in the surrounding water. In this treatment, DO was also significantly positively correlated with DOC concentration. Seagrass produced higher amounts of DOC in sg+cr compared to coral incubations (1.2 ± 8.8 μM) by generating 21.6 ± 19.1 μM into the water column. DOC concentrations in the seawater were positively correlated with bacterial abundance. Bacteria are important in the recycling of carbon in the system of coexisting coral and seagrasses due to their use of DOC exuded from both seagrasses and coral, which, in turn, enhances the assimilation of carbon by corals. Therefore, the production of carbon in coral tissues increased when coral was incubated together with seagrass. Similarly, nutrient uptake was highest in the sg+cr incubations. In this environment, where seagrass and coral coexist, corals can utilize DOC exuded by seagrass to increase carbon assimilation via microbial activity, while seagrass can assimilate nutrients and microbially degraded DOC from coral metabolism in the environment.

DOI： 10.11450/seitaikogaku.26.81

CiNii Research

Publisher：Cellule MathDoc/Centre Mersenne  

The effects of elevated temperature and high pCO2 on the metabolism of Galaxea fascicularis were studied with oxygen and pH microsensors. Photosynthesis and respiration rates were evaluated from the oxygen fluxes from and to the coral polyps. High-temperature alone lowered both photosynthetic and respiration rates. High pCO2 alone did not significantly affect either photosynthesis or respiration rates. Under a combination of high-temperature and high-CO2, the photosynthetic rate increased to values close to those of the controls. The same pH in the diffusion boundary layer was observed under light in both (400 and 750 ppm) CO2 treatments, but decreased significantly in the dark as a result of increased CO2. The ATP contents decreased with increasing temperature. The effects of temperature on the metabolism of corals were stronger than the effects of increased CO2. The effects of acidification were minimal without combined temperature stress. However, acidification combined with higher temperature may affect coral metabolism due to the amplification of diel variations in the microenvironment surrounding the coral and the decrease in ATP contents.

DOI： 10.1016/j.crvi.2013.07.003

PubMed

CiNii Research

Language：English  

DOI： 10.1080/14786419.2013.768992

PubMed

CiNii Research

Publisher：Elsevier BV  

Bleaching affects corals worldwide. We studied the effects of high seawater temperature and bacterial challenges on bleaching, metabolism, and antioxidant defenses of coral. The coral Montipora digitata and five bacterial strains (Vibrio coralliilyticus, Vibrio harveyi, Paracoccus carotinifaciens, Pseudoalteromonas sp., and Sulfitobacter sp.) were used in an inoculation experiment. The bacteria were isolated from the bleached corals and their surrounding seawater. At normal temperatures, the bacteria did not cause coral bleaching and did not affect metabolism or antioxidant enzyme activities. However, bacterial challenges in addition to high-temperature stress resulted in coral bleaching, with a 70% decrease in zooxanthellae density compared with the control, a 25% decrease in photosynthetic efficiency (Fv/Fm), a 66% decrease in photosynthesis, and a 101% reduction in calcification activity. Tissue necrosis was observed in the most compromised branches. Respiration and activity levels of antioxidant enzymes were not affected. Corals under thermal stress alone showed signs of bleaching, but the changes in zooxanthellae density and metabolic rates were less severe than those under synergistic thermal stress and bacterial challenge. Among the bacteria examined, Sulfitobacter sp. had a greater capacity to enhance and accelerate the bleaching process under thermal stress. The mechanisms by which bacteria affect corals are not yet understood. Direct actions include infection and production of toxic substances by bacteria; indirect effects due to changes in the bacterial community under the influence of added bacteria must also be considered. Our results suggest that bacterial challenges combined with thermal stress can synergistically lead to negative outcomes in corals.

DOI： 10.1016/j.jembe.2012.11.011

CiNii Research

Language：Japanese   Publisher：The Society of Eco-Engineering  

Increase in sea surface temperature and excessive input of nutrient in reef waters, due to anthropogenic activities have been among the various factors responsible for bleaching and mortality of corals around the world. So, this study investigated the effects of elevated nitrate (NO₃) concentration and temperature on the coral, <i>Pocillopora damicornis</i>. Coral fragments were incubated for two days at different temperatures (27°C and 32°C) and NO₃ concentrations (∼0.4 μM and 10 μM). Following 48 hours of stress under 32°C and 10 μM NO₃, the nubbins were moved to 27°C and ambient (∼0.4 μM) NO₃ levels for 48 hours of recovery period. Maximum quantum yield (<i>F_v /F_m</i>) and maximum excitation pressure (<i>Qm</i>) at photosystem II indicated that combined effect of high temperature and high NO₃ were more severe and only corals under these conditions exhibited an incomplete recovery. Furthermore, zooxanthellae density and pigment data showed that the response mechanism of these coral nubbins were different from high temperature or high NO₃ stress only. Aftre the recovery phase, zooxanthellae density was higher (∼1.5 fold) whereas chlorophyll <i>a</i> per cell was lower (∼1.5 fold) than the control (27°C and ∼0.4 μM NO₃) for combined stress of high nitrate and temperature. On the other hand, xanthophyll ratio for these nubbins was still significantly higher than the control, thus showing a possible mechanism of recovery by dissipating excess loght energy as heat. Hence, this study showed that under thermal stress, high nitrate amplifies damage to the <i>in hospite</i> zooxanthellae of the coral <i>Pocillopora damicornis</i> and recovery of the holobiont is more diffi cult after the stress.

DOI： 10.11450/seitaikogaku.25.75

CiNii Research

Publisher：Elsevier BV  

In order to investigate the incorporation of Sr, Mg, and U into coral skeletons and its temperature dependency, we performed a culture experiment in which specimens of the branching coral (Porites cylindrica) were grown for 1 month at three seawater temperatures (22, 26, and 30 C). The results of this study showed that the linear extension rate of P. cylindrica has little effect on the skeletal Sr/Ca, Mg/Ca, and U/Ca ratios. The following temperature equations were derived: Sr/Ca (mmol/ mol) = 10.214(±0.229) � 0.0642(±0.00897) � T (C) (r 2 = 0.59, p < 0.05); Mg/Ca (mmol/mol) = 1.973(±0.302) + 0.1002 (±0.0118) � T (C) (r 2 = 0.67, p < 0.05); and U/Ca (lmol/mol) = 1.488(±0.0484) � 0.0212(±0.00189) � T (C) (r 2 = 0.78, p < 0.05). We calculated the distribution coefficient (D) of Sr, Mg, and U relative to seawater temperature and compared the results with previous data from massive Porites corals. The seawater temperature proxies based on D calibrations of P. cylindrica established in this study are generally similar to those for massive Porites corals, despite a difference in the slope of DU calibration. The calibration sensitivity of DSr, DMg, and DU to seawater temperature change during the experiment was 0.64%/C, 1.93%/C, and 1.97%/C, respectively. These results suggest that the skeletal Sr/Ca ratio (and possibly the Mg/Ca and/or U/Ca ratio) of the branching coral P. cylindrica can be used as a potential paleothermometer. 2011 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.gca.2011.05.010

CiNii Research

Publisher：Wiley  

<jats:title>Abstract</jats:title><jats:p>Various stresses induce the formation of reactive oxygen species (ROS) in biological cells. In addition to stress‐induced ROS, we studied the photochemical formation of hydroxyl radicals (˙OH), the most potent ROS, in coral tissues using phosphate buffer‐extracted solutions and a simulated sunlight irradiation system. ˙OH formation was seen in extracts of both coral host and endosymbiont zooxanthellae. This study is the first to report quantitative measurements of ˙OH photoformation in coral tissue extracts. Our results indicated that whether or not coral bleaching occurred, coral tissues and symbiotic zooxanthellae have the potential to photochemically produce ˙OH under sunlight. However, no significant difference was found in the protein content‐normalized formation rates of ˙OH between corals incubated under different temperatures and irradiance conditions. ˙OH formation rates were reduced by 40% by reducing the UV radiation in the illumination. It was indicated that UV radiation strongly affected ˙OH formation in coral tissue and zooxanthellae, in addition to its formation through photoinhibition processes.</jats:p>

DOI： 10.1111/j.1751-1097.2010.00802.x

PubMed

CiNii Research

Publisher：Elsevier BV  

Coral metabolism reflects the physiological condition of a coral colony. We studied coral metabolism using a continuous-flow, complete mixing (CFCM) experimental system. Small-size Goniastrea aspera coral colonies were incubated in the CFCM system with and without hydrogen peroxide (H2O2) added to the supplied seawater (0 µM H2O2 for 12 days; 0, 0.3, 3.0, and 30 µM H2O2 for 3 days, for each treatment) Without addition of H2O2, coral metabolism, including photosynthesis (gross primary productivity) and calcification, was relatively stable and there were no significant metabolic changes, suggesting that, without H2O2 added to the CFCM system, the corals did not suffer significant stress from the experimental system over a 12-day incubation period. When H2O2 was added, large decreases in photosynthesis and calcification were observed. The non-parametric Mann–Whitney U-test showed that there were statistically significant differences in photosynthesis after addition of 3.0 µM and 30 µM H2O2, compared with the control. We also found statistically significant differences in net calcification after addition of 30 µM H2O2. Thus, the incubation experiments suggest that higher H2O2 concentrations in seawater clearly influence coral metabolism. However, the results also suggest that the current seawater H2O2 level in Okinawa is not likely to pose significant acute effects on the metabolic activities of corals.

DOI： 10.1016/j.jembe.2008.11.013

CiNii Research

Publisher：Springer Science and Business Media LLC  

We examined quantitative changes in the metabolism of the coral Galaxea fascicularis caused by increases in both hydrogen peroxide (H2O2) concentration and seawater temperature. Seawater temperatures were maintained at 27 or 31°C in a well-controlled incubation chamber, and three levels of H2O2 concentration (0, 0.3, 3.0 μM) were used in experimental treatments. Gross primary production, calcification rates and respiration rates were all affected by increased H2O2 concentrations and high seawater temperatures. Individual treatments of high H2O2 or elevated seawater temperature alone caused significant declines in coral photosynthesis and calcification rates within the 3-day incubation period. The synergistic effect of high H2O2 combined with high seawater temperature resulted in a 134% increase in respiration rates, which surpassed the effect of either H2O2 or high seawater temperature alone. Our results suggest that both high H2O2 concentrations and elevated temperatures in seawater can strongly affect coral metabolism; however, these effects cannot be estimated by simply summing the effects of individual stress parameters.

DOI： 10.1007/s00227-008-1110-0

CiNii Research

Publisher：Elsevier BV  

A small-scale chamber experimental system was designed to study the effects of temperature on colony-level coral metabolism. The system continuously supplies fresh seawater to the chamber, where it is mixed immediately and completely with the seawater already present. This continuous-flow complete-mixing system (CFCM system), in conjunction with theoretical equations, allows quantitative determination of chemical uptake and release rates by coral under controlled environmental conditions. We used the massive hermatypic coral Goniastrea aspera to examine variations in pH, total alkalinity, and total inorganic carbon for 16 days at 27 degrees C under controlled light intensities (300 and 0 micromol m(-2) s(-1)). We confirmed the stability of the CFCM system with respect to coral photosynthetic and calcification fluxes. In addition, we obtained daily photosynthetic and calcification rates at different temperatures (27 degrees C, 29 degrees C, 31 degrees C, and 33 degrees C). When seawater temperature was raised from 31 degrees C to 33 degrees C, the gross primary production rate (Pgross) decreased 29.5%, and the calcification rate (G) decreased 85.7% within 2 days. The CFCM system allows quantitative evaluation of coral colony chemical release and uptake rates, and metabolism.

DOI： 10.1016/j.jprot.2008.01.014

PubMed

CiNii Research

Publisher：Elsevier BV  

We investigated the chemical composition and photochemical formation of hydroxyl (OH) radicals in the water-soluble fractions (WSF) of aerosol particles collected in Okinawa, Japan. Bulk aerosol samples were collected for 2–7 days at a time by a high-volume air sampler over a 3-month period. Major ions present in the WSF solutions were SO42−, Na+, and Cl−. Sulfate ion concentrations were much higher when Yellow Sand events occurred. The mass-based Cl−/Na+ ratio found in the WSF solutions averaged 49.7%, much lower than the ratio in seawater, indicating that chlorine was lost from the aerosol particles. A negative correlation (R=−0.67) was found between the Cl−/Na+ ratio and the concentration of non-sea-salt–SO42−. We confirmed the photochemical formation of OH radicals in the study samples using illumination experiments at 313 nm. The apparent quantum yields of OH radical photoformation, based on the total absorbance at 313 nm, ranged from ND to 0.0017, with a mean±1 SD of 0.0010±0.0005. Hydroxyl radical photoformation rates from nitrate and nitrite photolyses, estimated based on nitrate and nitrite ion concentrations and our illumination conditions, averaged 32±24% and <10%, respectively, of the total formation rates. Hydroxyl radical photoformation rates were strongly correlated with total dissolved iron concentrations (R=0.88). A correlation also existed between OH radical photoformation rates and dissolved organic carbon concentrations (R=0.69).

DOI： 10.1016/j.atmosenv.2006.04.035

CiNii Research