Characterization of diversity and community structure of small planktonic copepods in the Kuroshio region off Japan using a metabarcoding approach

Small copepods are important prey for fish larvae in the Kuroshio region off southern Japan. However, revealing entire community structures of small copepods is difficult using conventional methods. We applied a metabarcoding method to size-fractionated community samples of epipelagic copepods (small: 0.1-0.5 mm, medium: 0.5-1.0 mm, and large: 1.0-2.0 mm). Samples were collected from 2013 to 2016 from the shoreward (Kuroshio Slope, KS) and oceanic (Kuroshio Gyre, KG) sides of the Kuroshio Current at 138° E; the results were compared with those in the center of the subtropical gyre (SG). The KS and KG sites showed both spatial differences and seasonal changes, with distinct differences between winter-spring and summer-autumn in each size-fractionated community. Water temperature markedly influenced copepod diversity and community structure, especially in the small size fraction. Warm-water species in the SG intruded into the Kuroshio regions during high-temperature periods, leading to high diversity in summer-autumn. Inter-annual environmental variations influenced by temperature and productivity were evident in KS, leading to clear changes in the sequence proportions of dominant small copepods including Paracalanus sp. and immature stages of the large copepod Calanus sinicus. Immature stages of medium/large copepods formed a substantial proportion of small-copepod communities in the Kuroshio regions (KS: 28.8%; KG: 24.7%; SG: 11.9%; based on average proportions of sequence reads). Because of their ecological importance and sensitivity to environmental changes, monitoring communities of small copepods with high taxonomic resolution may provide further insights into marine ecosystems, including fish recruitment, in the Kuroshio region.

Download Full-text

Biomarkers in the rock outcrop of the Kazusa Group reveal palaeoenvironments of the Kuroshio region

Communications Earth & Environment ◽

10.1038/s43247-021-00154-2 ◽

2021 ◽

Vol 2 (1) ◽

Author(s):

Hiroto Kajita ◽

Ayumi Maeda ◽

Masayuki Utsunomiya ◽

Toshihiro Yoshimura ◽

Naohiko Ohkouchi ◽

...

Keyword(s):

Sediment Cores ◽

Kuroshio Current ◽

Sea Surface ◽

Average Chain Length ◽

Rock Outcrop ◽

Diagenetic Alteration ◽

Organic Biomarkers ◽

The Kuroshio ◽

Kuroshio Region ◽

Long Chain

AbstractLong-chain alkenones and n-alkanes preserved in marine and lake sediment cores are widely used to reconstruct palaeoenvironments. However, applying this technique to exposed sedimentary rock sequences is relatively challenging due to the potential for the diagenetic alteration of organic biomarkers. Here, we extract long-chain alkenones and n-alkanes from an exposed outcrop of the Kazusa Group in central Japan, one of the most continuous sedimentary successions in the world, covering almost the entire Pleistocene. We find that the alkenone unsaturation ratio and average chain length of n-alkanes appears to reflect the glacial-interglacial changes in sea surface temperature and terrestrial climate, respectively. Alkenone-based sea surface temperatures between 1.1 and 1.0 million years ago concur with foraminiferal Mg/Ca-based temperature estimates and may reflect an intrusion of the Kuroshio Current. We suggest that the preservation of these biomarkers in the Kazusa Group demonstrates its potential to provide a detailed palaeoenvironmental record.

Download Full-text

Summer Phytoplankton community Structure in the Kuroshio Current-related Upwelling Northeast of Taiwan

Terrestrial Atmospheric and Oceanic Sciences ◽

10.3319/tao.1992.3.3.305(keep) ◽

1992 ◽

Vol 3 (3) ◽

pp. 305 ◽

Cited By ~ 19

Author(s):

Yuh-Ling Chen Lee

Keyword(s):

Community Structure ◽

Phytoplankton Community ◽

Kuroshio Current ◽

Phytoplankton Community Structure ◽

The Kuroshio

Download Full-text

Biomarkers in the rock outcrop of the Kazusa Group reveal paleoenvironments of the Kuroshio region

10.21203/rs.3.rs-72985/v1 ◽

2020 ◽

Author(s):

HIROTO KAJITA ◽

Ayumi Maeda ◽

Masayuki Utsunomiya ◽

Toshihiro Yoshimura ◽

Naohiko Ohkouchi ◽

...

Keyword(s):

Sediment Cores ◽

Kuroshio Current ◽

Sea Surface ◽

Average Chain Length ◽

Rock Outcrop ◽

Central Japan ◽

Sedimentary Succession ◽

Atmospheric Changes ◽

The Kuroshio ◽

Kuroshio Region

Abstract The classical biomarkers of long-chain alkenones and n-alkanes preserved in marine and lake sediment cores are widely used to reconstruct paleoenvironments. Here, we detected these biomarkers are preserved in the rock outcrop of the Kazusa Group exposed in central Japan, the most continuous sedimentary succession in the world, covering almost the entire Pleistocene. The alkenone unsaturation ratio and average chain length of n-alkanes appeared to reflect the glacial-interglacial changes in the sea surface temperature (SST) and terrestrial climate, respectively. Alkenone-based SSTs during 1.1–1.0 Ma were significantly higher than present-day SSTs in the same area, as supported by foraminiferal Mg/Ca-based temperatures, possibly reflecting the direct intrusion of the warm Kuroshio Current. Applying these biomarkers, which might be circumstantially preserved owing to their immunity to high temperature and consolidation stress during burial and uplift, we expect that the Kazusa Group should reveal detailed oceanic and atmospheric changes of the Kuroshio region.

Download Full-text

The turnstile mechanism across the Kuroshio current: analysis of dynamics in altimeter velocity fields

Nonlinear Processes in Geophysics ◽

10.5194/npg-17-103-2010 ◽

2010 ◽

Vol 17 (2) ◽

pp. 103-111 ◽

Cited By ~ 27

Author(s):

C. Mendoza ◽

A. M. Mancho ◽

M.-H. Rio

Keyword(s):

Kuroshio Current ◽

Transport Processes ◽

Data Sets ◽

Current Analysis ◽

Stable And Unstable Manifolds ◽

Unstable Manifolds ◽

Hyperbolic Trajectories ◽

Analysis Of Dynamics ◽

The Kuroshio ◽

Kuroshio Region

Abstract. In this article we explore the utility of dynamical systems tools for visualizing transport in oceanic flows described by data sets measured from satellites. In particular we have found the geometrical skeleton of some transport processes in the Kuroshio region. To this end we have computed the special hyperbolic trajectories, and identified them as distinguished hyperbolic trajectories, that act as organizing centres of the flow. We have computed their stable and unstable manifolds, and they reveal that the turnstile mechanism is at work during several spring months in the year 2003 across the Kuroshio current. We have found that near the hyperbolic trajectories takes place a filamentous transport front-cross the current that mixes waters from both sides.

Download Full-text

Analysis of nifH DNA and RNA reveals a disproportionate contribution to nitrogenase activities by rare plankton-associated diazotrophs

10.21203/rs.2.9602/v2 ◽

2019 ◽

Author(s):

Qingsong Yang ◽

Junde Dong ◽

Manzoor Ahmad ◽

Juan Ling ◽

Weiguo Zhou ◽

...

Keyword(s):

Community Structure ◽

Environmental Changes ◽

Northern South China Sea ◽

Nifh Gene ◽

Size Fraction ◽

Alpha Diversity ◽

Equal Proportion ◽

Dna And Rna ◽

Abundant Otus ◽

Nitrogenase Activities

Abstract Abstract Background: Holobionts comprising nitrogen-fixing diazotrophs and phytoplankton or zooplankton are ubiquitous in the pelagic sea. However, neither the community structure of plankton-associated diazotrophs (PADs) nor their nitrogenase transcriptional activity are well-understood. In this study, we used nifH gene Illumina sequencing and quantitative PCR to characterize the community composition and nifH expression profile of PADs with > 100 µm size fraction in the euphotic zone of the northern South China Sea. Results: The results of DNA- and RNA-derived nifH gene revealed a higher alpha-diversity in the active than in the total community. Moreover, the compositional resemblance among different sites was less for active than for total communities of PADs. We characterized the 20 most abundant OTUs by ranking the sum of sequence reads across 9 sampling stations for individual OTUs in both nifH DNA and RNA libraries, and then assessed their phylogenetic relatedness. Eight of the 20 abundant OTUs were phylogenetically affiliated with Trichodesmium and occurred in approximately equal proportion in both the DNA and RNA libraries. The analysis of nifH gene expression level showed uneven attribute of the abundance and nitrogenase activities by the remaining 12 OTUs. Taxa belonging to cluster III and Betaproteobacteria were present at moderate abundance but exhibited negligible nitrogenase transcription activity. Whereas, the abundances of Richelia, Deltaproteobacteria and Gammaproteobacteria were low but the contribution of these groups to nitrogenase transcription was disproportionately high. Conclusions: The substantial variation in community structure among active dizatrophic fractions compared to the total communities suggests that the former are better indicators of biological response to environmental changes. Altogether, our study highlights the importance of rare PADs groups in nitrogen fixation in plankton holobionts, evidenced by their high level of nitrogenase transcription.

Download Full-text

Calcareous nannofossil biostratigraphy of the Lower–Middle Pleistocene boundary of the GSSP, Chiba composite section in the Kokumoto Formation, Kazusa Group, central Japan, and implications for sea-surface environmental changes

Progress in Earth and Planetary Science ◽

10.1186/s40645-020-00355-x ◽

2020 ◽

Vol 7 (1) ◽

Cited By ~ 1

Author(s):

Koji Kameo ◽

Yoshimi Kubota ◽

Yuki Haneda ◽

Yusuke Suganuma ◽

Makoto Okada

Keyword(s):

Environmental Changes ◽

Kuroshio Current ◽

Sea Surface ◽

Middle Pleistocene ◽

Calcareous Nannofossil ◽

Central Japan ◽

Composite Section ◽

Calcareous Nannofossil Biostratigraphy ◽

The Kuroshio ◽

Millennial Scale

Abstract The Chiba composite section (CbCS), in the middle of the Boso Peninsula in central Japan, was ratified as the Global Boundary Stratotype Section and Point (GSSP) for the Lower–Middle Pleistocene boundary, accompanied by the Matuyama–Brunhes (M–B) paleomagnetic polarity boundary in January 2020. This study examined the calcareous nannofossil biostratigraphy of the CbCS to describe potential nannofossil events and discuss sea-surface environments around the M–B paleomagnetic polarity boundary. There are no clear biohorizons at the M–B paleomagnetic polarity boundary, although a temporary disappearance of Gephyrocapsa specimens (≥ 5 μm in diameter), an important calcareous nannofossil genus in the Pleistocene, occurs just above the Lower–Middle Pleistocene boundary. Although this is a characteristic event around the M–B paleomagnetic polarity boundary, it is unclear whether the event is globally traceable. Changes in the environmental proxy taxa of calcareous nannofossils in the CbCS revealed that sea-surface environments were driven by glacial-interglacial and millennial-scale climate forces. The time-transgressive change of the Tn value, a calcareous nannofossil temperature index, is mostly concordant with the planktonic foraminiferal oxygen isotope fluctuation. Abundant occurrences of a warm-water species, Umbilicosphaera spp., indicate that the Kuroshio Current was strong after ~ 783 ka. Even the strong influence of the Kuroshio Current, cooling events related to southward movements of the Kuroshio Front occurred every 10,000 years based on the presence of a cold-water taxon, Coccolithus pelagicus. Additionally, the inflow of coastal waters strengthened after ~ 778 ka because of abundant occurrences of Helicosphaera spp. Millennial-scale sea-surface changes were also inferred from detected floral fluctuations of less than 10,000 years. Graphical abstract

Download Full-text

DIVERSITY OF FISH LARVAE AROUND THE ESTUARY OF THE BANYUASIN RIVER, SOUTH SUMATERA PROVINCE

BIOVALENTIA Biological Research Journal ◽

10.24233/biov.6.2.2020.181 ◽

2020 ◽

Vol 6 (2) ◽

Author(s):

Moh. Rasyid Ridho ◽

Enggar Patriono ◽

Sarno Sarno ◽

Sahira Wirda

Keyword(s):

Initial Phase ◽

Sampling Method ◽

Environmental Changes ◽

Negative Impact ◽

Fish Larvae ◽

River Estuary ◽

Sampling Technique ◽

Critical Phase ◽

Morisita Index ◽

Index Value

The initial phase of the fish life cycle is a critical phase associated with high mortality due to sensitivity to predators, food availability, and also environmental changes that occur in nature. Disruption of the initial stages of fish life has a negative impact on fish populations. Until now there has been no information about fish larvae around the Banyuasin River Estuary. Therefore, research is needed on the diversity of fish larvae around the Banyuasin River Estuary, South Sumatra Province. This research were used purposive sampling method, sampling technique in the form of Cruise Track Design with continuous parallel survey trajectory. Based on the results of the study found as many as 10 families consisting of 1483 individuals of fish larvae in March and 1013 individuals of fish larvae in May consisting of Engraulidae 1,601 individuals of fish larvae, Mungiloidei as many as 109 individuals, Leiognathidae 50 individuals, Chanidae 453 individuals, Scatophagidae 20 individuals , Belonidae 39 individuals, Gobioididae 5 individuals, Chandidae 183 individuals, Syngnatihidae 6 individuals, and Gobiidae 30 individuals fish larvae. The index value of fish larvae diversity is classified as medium category (March 1.02 and May 1.12), Morisita index shows the distribution pattern of fish larvae classified as a group (March 0-14.17 and May 2.43-10.40 ), and the evenness index value is in the medium category (March 0.437 and May 0.521).

Download Full-text