Rapid profiling of tropical marine cyanobacterial communities

Cyanobacteria are important organisms in the marine ecosystem as they play vital roles in nutrient cycling and oxygen production. In this study, tropical marine cyanobacterial communities from various sites in Southeast Asia and their associated ecological parameters were examined. 16S rRNA sequences of 1502 bp were obtained for barcode amplicon sequencing using the Nanopore MinION™ sequencing platform. Planktonic and benthic cyanobacteria were observed with total of 40 genera and 46 species of cyanobacteria identified from sites in Sabah and Singapore. Species richness analyses showed that the cyanobacterial community from the West Johor Strait was approximately two times greater than that of the East Johor Strait and the Singapore Strait. This is due to the variability in ecological parameters measured between sites such as rainfall, salinity and temperature. This is the first study that has employed this technology for phytoplankton samples with species resolution, providing insight to the diversity of cyanobacteria present in tropical marine ecosystems. Furthermore, the portability of this sequencer enables the real-time monitoring of coastal environments for the specific detection and identification of harmful algal bloom species

Characterization of the phytoplankton size composition and light absorption coefficient in the temperate coastal waters of Sagami Bay

Phytoplankton constitute the base of the aquatic food web and are the primary driver of biogeochemical processes such as the e port of carbon to the deep ocean. Knowledge of the distributions, compositions, and biomass of the phytoplankton community are essential to under stand biogeochemical cycles. Phytoplankton can be enumerated by microscopy, but this requires e tensive time for sample preparation and counting, especially if statistically valid counts of the less abundant phytoplankton classes are required. Further, smaller picoplankton can be difficult to identify since they lack ta onomically e ternal morphological features. Thus, the accessory pigment-based model has been used to estimate phytoplankton communities based on their size classes: micro- (M; > 20 µm), nano- (N; 2-20 µm) and pico-phytoplankton (P; < 2 µm). Light absorption by phytoplankton has a direct influence on the optical properties of seawater, and there is a growing effort to develop approaches to identify the spatial and temporal variability of the phytoplankton community from satellites. However, estimating the phytoplankton com munity in optically comple coastal waters from satellites is still a challenging problem because phytoplankton are only one of multiple optically significant constituents of seawater. Also, there are limitations of wavelength that satellites can measure, and overlapping signature pigment of each phytoplankton community. In order to improve the estimation of phytoplankton communi ties, it is necessary to understand the light absorption coefficient of phytoplankton, aph (,,) asso ciated with the varying community structure. The objective of this study was to characterize the variability of phytoplankton size classes and their light absorption coefficients in the temperate coastal waters of Sagami Bay. The specific objectives were (1) to classify phytoplankton com munities based on cell size, (2) to investigate co-variability of aph (,,) spectra according to the classification. The present study conducted in situ observations from April 2016 to September 2022 at Station M (St. M: 35° 09’ 45” N, 139° 10’00” E) in the temporal coastal waters of Sagami Bay, Japan. Water samples for pigments and light absorption properties of phytoplankton were collected from surface water with a bucket, and measured by high-performance liquid chroma tography and spectrophotometry, respectively. Phytoplankton size class composition was esti mated based on pigment concentrations. The results showed that the three groups (Group M, N, P) generated according to the phytoplankton size composition were significantly different (R = 0.646, p < 0.001). Also, the most dominant group throughout the study period was microplank ton (n = 110). The aph (,,) spectra showed peaks around 438 nm and 465 nm in the blue band and 674 nm in the red band. Using three wavelengths peaks, although the aph (,,) of group M was sig nificantly higher than that of group N, Group P was not significantly different from other groups. This study suggests that the aph (,,) spectrum in the temperate coastal waters of Sagami Bay is significantly co-varying with the variability of phytoplankton size composition. The results sug gest that analyzing the difference in aph (,,) spectra ratios and performing derivative analysis, coupled with analysis of phytoplankton size distribution and pigment composition should im prove our ability to characterize phytoplankton spatio-temporal distribution from space.departmental bulletin pape

Practical Science and Environmental Education Workshop in Manaus, Brazil

It is an unequivocal fact that Amazonian tropical forest is the largest remaining primary forest in the world. The ecosystem in the region is e tremely comple with high biodiversity (Peres et al. 2010). Conservation and protection of the dynamic forest and river regions is e tremely important not only for the natural environments, but also for the economy and social dependence of benefits from such abundant natural environments. Important natural parameters that affect status of the natural environments include light (natural sunlight), soil, and water, which abundantly e ist in the Amazon region. Solar energy is the primary energy source for the majority of living organisms in both terrestrial and aquatic ecosystems, and drives the diurnal and seasonal cycles of biogeochemical processes (Monteith & Unsworth 2013). In particular, in situ light data remains one of the most underappreciated data measurements although having a significant impact on the physical, chemical and biological processes in the ecosystem (Johnsen 2012). Soil provides the fundamental basis for all terrestrial living organisms including the Amazonian forests as well as life-sustaining infrastructure for human society. Water is the most essential single entity to constitute all organisms from a single cell to the earth. Understanding of importance and roles of each factor and interaction of such comple dynamics in the natural environments can serve as fundamental platform for natural scientists, particularly for young scientists such as university students. The objective of this workshop was to provide hand- on scientific and environmental education for university students in Manaus, Amazonas, Brazil through practical field measurements using the three most important parameters in the natural ecosystem composed of natural sunlight, soil, and water. The workshop was divided into a series of lectures, in situ field sampling, and data processing, analysis and interpretation with the ultimate goal of empowering the undergraduate students with research-centered environmental education and e perience of developing international collaboration.departmental bulletin pape

Size-dependent absorption property of phytoplantkon in the Southern Ocean

第2回極域科学シンポジウム　共通セッション「海氷圏の生物地球化学」 11月16日（水） 統計数理研究所 3階セミナー

Search for gravitational-lensing signatures in the full third observing run of the LIGO-Virgo network

Gravitational lensing by massive objects along the line of sight to the source causes distortions of gravitational wave-signals; such distortions may reveal information about fundamental physics, cosmology and astrophysics. In this work, we have extended the search for lensing signatures to all binary black hole events from the third observing run of the LIGO--Virgo network. We search for repeated signals from strong lensing by 1) performing targeted searches for subthreshold signals, 2) calculating the degree of overlap amongst the intrinsic parameters and sky location of pairs of signals, 3) comparing the similarities of the spectrograms amongst pairs of signals, and 4) performing dual-signal Bayesian analysis that takes into account selection effects and astrophysical knowledge. We also search for distortions to the gravitational waveform caused by 1) frequency-independent phase shifts in strongly lensed images, and 2) frequency-dependent modulation of the amplitude and phase due to point masses. None of these searches yields significant evidence for lensing. Finally, we use the non-detection of gravitational-wave lensing to constrain the lensing rate based on the latest merger-rate estimates and the fraction of dark matter composed of compact objects

Search for eccentric black hole coalescences during the third observing run of LIGO and Virgo

Despite the growing number of confident binary black hole coalescences observed through gravitational waves so far, the astrophysical origin of these binaries remains uncertain. Orbital eccentricity is one of the clearest tracers of binary formation channels. Identifying binary eccentricity, however, remains challenging due to the limited availability of gravitational waveforms that include effects of eccentricity. Here, we present observational results for a waveform-independent search sensitive to eccentric black hole coalescences, covering the third observing run (O3) of the LIGO and Virgo detectors. We identified no new high-significance candidates beyond those that were already identified with searches focusing on quasi-circular binaries. We determine the sensitivity of our search to high-mass (total mass M&gt;70 M⊙) binaries covering eccentricities up to 0.3 at 15 Hz orbital frequency, and use this to compare model predictions to search results. Assuming all detections are indeed quasi-circular, for our fiducial population model, we place an upper limit for the merger rate density of high-mass binaries with eccentricities 0&lt;e≤0.3 at 0.33 Gpc−3 yr−1 at 90\% confidence level

Ultralight vector dark matter search using data from the KAGRA O3GK run

Among the various candidates for dark matter (DM), ultralight vector DM can be probed by laser interferometric gravitational wave detectors through the measurement of oscillating length changes in the arm cavities. In this context, KAGRA has a unique feature due to differing compositions of its mirrors, enhancing the signal of vector DM in the length change in the auxiliary channels. Here we present the result of a search for U(1)B−L gauge boson DM using the KAGRA data from auxiliary length channels during the first joint observation run together with GEO600. By applying our search pipeline, which takes into account the stochastic nature of ultralight DM, upper bounds on the coupling strength between the U(1)B−L gauge boson and ordinary matter are obtained for a range of DM masses. While our constraints are less stringent than those derived from previous experiments, this study demonstrates the applicability of our method to the lower-mass vector DM search, which is made difficult in this measurement by the short observation time compared to the auto-correlation time scale of DM

Marine microplastics in the ASEAN region: A review of the current state of knowledge

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