Reproductive ecology of dominant dinoflagellate, Ceratium furca, in the coastal area of Sagami Bay

Reproductive ecology of dinoflagellate, Ceratium furca, was studied in the coastal area of Sagami Bay. Field samplings and laboratory experiments were conducted to investigate seasonal changes of the field population and effects of temperature, salinity and irradiance on the growth rate of C. furca. Abundance of the species increased significantly from April to September and was decreased in November. In particular, the population increased during the spring when the water column was weakly stratified and relatively low nutrient conditions were observed in the surface layer. High growth rates of C. furca were observed at the conditions of 20-28℃, 17-34 PSU and 216-800μEm^s^ with the highest growth rate (μ=0.72d^) being observed at 24℃, 30 PSU and 600μEm^s^. In addition, the growth rates increased gradually with increasing irradiance from 58 to 216μEm^s^ in the all salinity conditions, and afterwards the rates reached plateaus between 216 and 796μEm^s^. The field survey and laboratory experiments indicated that the species is distributed throughout the year and adapted to a wide-range of environmental fluctuations such as water temperature, salinity, irradiance and nutrients. These specific characteristics make C. furca one of the dominant dinoflagellates in the coastal area

Reproductive strategy of Acartia steueri in Sagami Bay, Japan

Reproduction, hatching success and population dynamics of the dominant copepod Acartia steueri were studied in Sagami Bay, Japan from February 2002 to December 2003. A. steueri occurred through the year in the water column, and it produced physiologically different eggs, subitaneous and diapausing. Subitaneous eggs were produced through the experimental period, whereas diapausing ones were restricted from February to August in both years. Population egg production rate (EPR) increased with the abundance of adult males and females from February and reached maximum in June. However, planktonic population of A. steueri did not increase during summer to winter because diapausing eggs occupied a great part of their reproduction (～98%). Recruitment rates in October to December 2002 and September 2003 were higher than population EPR, implying that diapausing eggs of A. steueri had a key role to support the recruitment into water column when the reproductive ability of the population diminished rather than to contribute to an increase of the planktonic population rapidly in their favorable seasons

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

カイアシ類1 個体からのDNA 抽出方法の改良とホルマリン固定期間がミトコンドリア遺伝子のPCR増幅に与える影響

　Considerable skill is required to identify copepods at the species level based on their morphological characteristics. However, DNA analysis does not require advanced microscopy techniques and provides objective data on the phylogenetic relationships between samples. Therefore, DNA analysis is useful as an alternative method for taxonomic studies of copepods. The lysis buffer method by Lee & Frost (2002) is a simple protocol for extracting DNA from single copepod samples. In this method, a fixative, such as formalin, is first replaced with ethanol and a buffer solution. Then, the copepod sample is lysed in the lysis buffer containing a proteolytic enzyme. Thus far, we have conducted DNA extraction of single copepod samples using this method and performed gene amplification by PCR. However, due to the low success rate of PCR amplification, genetic data could not be obtained for approximately 50% of the formalin-fixed samples. In this study, we improved the lysis buffer method with the aim of enhancing the success rate of DNA extraction and PCR amplification from single copepod samples. In addition, the effect of formalin fixation time on PCR amplification was also examined.Zooplankton samples were collected from Manazuru Port, Sagami Bay on September 14, 2017, using a plankton net with a mesh size of 180 μm and fixed with 5% neutralized formalin-seawater. Adult females of the calanoid copepod Acartia japonica were selected from these samples and stored individually in ethanol. DNA was extracted from these copepods via a modified ethanol removal method, with adjustments made to the dilution of the lysis buffer, and incubation time. The mitochondrial cytochrome b gene was amplified from these DNA samples by PCR. When the concentration of the PCR product was 20 ng μL-1 or more, PCR amplification was considered to be successful. Based on the conditions optimized by the above studies, the effect of the formalin fixation time on the PCR amplification of copepods was also investigated. A higher success rate was obtained when natural drying or vacuum drying was performed to remove ethanol during DNA extraction rather than removal by pipetting. Since there was no significant difference between the results of natural drying and vacuum drying, natural drying, which is easier to perform, was selected as the optimum method. We also confirmed that a high success rate was maintained without diluting the lysis buffer after the inactivation of proteolytic enzyme. Regarding the incubation time for lysis, changing from the conventional 60 minutes to 30 minutes did not result in a significant decrease in the success rate of PCR amplification. Thus, the success rate of PCR increased to approximately 90%. Additionally, compared with the conventional lysis buffer method, the number of steps was reduced by half, and the required time was shortened from 1.5 hours to approximately 50 minutes. Furthermore, we confirmed that this improved lysis buffer method can be applied to single cells of small protozoa such as flagellates and ciliates. The effect of formalin fixation time on PCR amplification of the mitochondrial cytochrome b gene after DNA extraction via this improved lysis buffer method was investigated. As expected, the success rate of PCR amplification decreased with the formalin fixation time. However, when the fixation period was within 1 month, PCR products with a concentration of more than 20 ng μL-1 were obtained in 95% of the individual copepod samples. Furthermore, even after 3 months, similar concentrations of PCR product were obtained in 80% of individuals.Genetic analysis of small zooplankton is increasingly important not only in taxonomy but also for biodiversity and phylogeographic studies. The data presented in this study will be very important and useful in such studies

25年ぶりに相模湾で発生した円石藻Gephyrocapsa oceanicaによるブルーム

Coccolithophore is one type of phytoplankton that forms calcium carbonate plates called coccoliths, and is relatively diverse with about 200 species in the worldʼs oceans. Coccoliths accumulate in massive calcareous deposits on the sea floor that serve as a sedimentary buffer of ocean chemistry and are also a major long-term carbon storage that has a significant impact on the global carbon cycle and climate. Coccolithophores are also a major producer of dimethyl sulfide (DMS) that is the dominant precursor for cloud condensation nuclei in the marine atmosphere; DMS emissions decrease solar radiation due to increasing cloud cover. Coccolithophores play an important role in biogeochemical cycles in the ocean by influencing the oceanic uptake of atmospheric carbon dioxide, and producing calcium carbonate sediments and DMS. Coccolithophores often bloom on massive scales. Around the Japan archipelago, coccolithophore blooms have also been reported; a Gephyrocapsa oceanica bloom in Tokyo Bay and Sagami Bay (1995) and Hakata Bay (2004, 2007, 2008), and a Emiliania huxleyi bloom in Suruga Bay (2007). In mid-May 2020, a massive bloom of coccolithophores were observed in Sagami Bay, Japan, possibly for the first time in 25 years. The bloom was initially observed by the JAXA, GCOM-C ocean color remote sensing satellite “Shikisai” capturing a vast emerald green reflectance image in the bay. Researchers who received the report immediately conducted in situ observations, and found that coccolithophores caused the massive bloom. Coccolithophore is a common yet elusive group in the waters around Japan, and there has only been one report of a bloom observation in Sagami Bay. This study shows the characteristics of the coccolithophore bloom observed in Sagami Bay in 2020 and also reports on the marine environment during the bloom. Water temperature, salinity, nutrients, chlorophyll a, and cell density were collected from field samples. Satellite ocean color data was provided by “Shikisai”. Satellite images on May 13 and 17 in 2020 show that the bloom spread counterclockwise due to counterclockwise coastal currents in Sagami Bay. The species, Gephyrocapsa oceanica, was confirmed using light microscopy and a scanning electron microscope, and was the same species that occurred in 1995. Chlorophyll a concentration and cell density at the surface were 1.2 μg L-1 and 9.0×103 cells mL-1, respectively. NO2- and NO3-concentrations at the surface during the bloom were 0.10 μmol L-1 and 1.83 μmol L-1, respectively, which were relatively higher than previous years. The results suggest that one of the causes of coccolithophore bloom is the relatively high concentration of inorganic nitrogen. Previous studies of prokaryotic and eukaryotic community structure in the coastal areas of Sagami Bay using genetic analysis have reported occurrence of haptophytes and the occurrence of coccolithophores throughout the year. These results suggest that coccolithophores are frequently present in Sagami Bay and form massive blooms in a short time period if environmental conditions are favorable. Further investigation including culture experiments are needed to resolve the details and specific causes

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

タナベワン ニ オケル ヤカン フジョウセイ カイアシルイ ノ セイタイ

京都大学0048新制・課程博士博士(理学)甲第9369号理博第2504号新制||理||1298(附属図書館)UT51-2002-G127京都大学大学院理学研究科生物科学専攻(動物学系)(主査)教授 白山 義久, 教授 堀 道雄, 教授 今福 道夫学位規則第4条第1項該当Doctor of ScienceKyoto UniversityDA