The Experts below are selected from a list of 49284 Experts worldwide ranked by ideXlab platform
Seiji Ohsumi - One of the best experts on this subject based on the ideXlab platform.
-
functional reduction of the southern minke whale balaenoptera acutorostrata testis during the feeding season
Marine Mammal Science, 2000Co-Authors: Toshihiro Mogoe, Hajime Ishikawa, Yutaka Fukui, Takatoshi Suzuki, Masatsugu Asada, Seiji OhsumiAbstract:Seasonal variation in reproductive activity in the male southern minke whales was investigated. The animals were killed and collected during the feeding season (December-March) in the Antarctic Ocean in the eastern part of Area III (35°E-70°E, south of 60°S) and Area IV (70°E-130°E, south of 60°S). Blood samples, testes, epididymides, and vasa deferentia were collected from 62 males, which had testes weighing over 400 g each. Changes in testicular morphology and plasma testosterone, estradiol-17β and LH concentrations measured by enzyme immunoassay were investigated. Reduction of testicular function associated with different capture periods was found in the summer season. From December to March, body length and body weight remained steady, but decreases in testicular weight, epididymal weight, and testicular volume were found in February. During the same period, plasma testosterone concentration also declined. A significant decrease in the number of germ cells continued during the period of feeding season. An increase in area of seminiferous tubule tended to proceed in a number of germ cells. These changes reflected the percentage of spermatozoa in the vasa deferentia; in particular, motile spermatozoa were observed in December. Based on morphological observation, spermatogenesis had also declined. These results indicate regulation of testicular function by testosterone, as in terrestrial mammals. A gradual decrease of testicular function occurred during December-January.
-
in vitro fertilization of in vitro matured minke whale balaenoptera acutorostrata follicular oocytes
Marine Mammal Science, 1997Co-Authors: Yutaka Fukui, Hajime Ishikawa, Toshihiro Mogoe, Seiji OhsumiAbstract:In vitro fertilization of follicular oocytes harvested from ovaries and matured in vitro was attempted for 55 minke whales (Balaenoptera acutorostrata) captured for Japanese research purposes in the Antarctic Ocean during the period from November 1995 to March 1996. In Experiment 1, effects of culture duration (96 h or 120 h) on maturation of follicular oocytes and addition of caffeine (5 mM) and/or heparin (100 pg/ml) on sperm penetration and pro-nuclear formation were investigated. Spermatozoa recovered from the vasa deferentia of four mature males were diluted (5-fold) and frozen at - 80°C. The post-thawed and pooled spermatozoa were used for in vitro insemination. A higher (P < 0.05) proportion of the oocytes cultured for 120 h (34.2% of 260) progressed beyond the second metaphase stage than of the oocytes cultured for 96 h (26.0% of 262). For the matured oocytes, higher rates of penetration (P < 0.05) and pronuclear formation (P < 0.01) were obtained in the oocytes cultured for 120 h (55.1% and 40.4%) than in those cultured for 96 h (32.4 % and 20.6%). Addition of caffeine and heparin did not show a significant effect. In Experiment 2, follicular oocytes matured for 120 h and then inseminated were cultured to examine the subsequent development in two culture systems (with and without co-cultured cumulus cells). Of 448 inseminated oocytes, cleaved embryos (2–16 cells) were observed with (5.8%) and without (4.9%) co-cultured systems. No cleavage was observed in 54 ova without insemination. These results indicate that in vitro fertilization of minke whale in vitro matured follicular oocytes with cryopreserved spermatozoa is possible, yielding cleaved embryos.
Marie Anne Vincendeau - One of the best experts on this subject based on the ideXlab platform.
-
recycling of organic matter in Antarctic sediments a transect through the polar front in the southern Ocean indian sector
Limnology and Oceanography, 1998Co-Authors: Christophe Rabouille, Jeanfrancois Gaillard, Paul Treguer, J C Relexans, Marie Anne VincendeauAbstract:Sediments from the Polar Front Zone were sampled in the Indian Sector of the Antarctic Ocean as part of the French JGOFS expedition Antares 1. The first porewater distributions of O2 and NO3= and organic carbon data in the solid phase in this part of the Ocean were used to model the recycling of organic matter in sediments. The data are described by a model containing two types of degradable organic matter with distinct reactivities. We estimate that the reactivity of the most labile organic carbon is very close to that of fresh organic matter with an average C : N ratio of 7. We estimate that particulate organic carbon fluxes deposited at the sediment-water interface range between 0.2 and 0.8 mol C m−l y−l, with two peaks near the Polar Front and the SubAntarctic Front. The flux 01 organic carbon deposited at the sediment-water interface is unusually high and represents ˜10–20% of estimated primary production. From these findings, we conclude that production in the pelagic zone of this region is strongly linked to deposition and recycling in the sediment.
-
biogenic silica recycling in surficial sediments across the polar front of the southern Ocean indian sector
Deep-sea Research Part Ii-topical Studies in Oceanography, 1997Co-Authors: Christophe Rabouille, Jeanfrancois Gaillard, Paul Treguer, Marie Anne VincendeauAbstract:Abstract The processes controlling preservation and recycling of particulate biogenic silica in superficial sediments must be understood before one uses biogenic silica as a proxy in paleoOceanographic studies, and in order to compute Oceanic mass balances for silica. In this respect, the Antarctic Ocean is certainly a key region due to its high productivity and export of biogenic silica. In order to quantify sedimentary fluxes and identify crucial processes that allow the preservation of biogenic silica, pore water and solid phase silica profiles were performed on sediment cores from the Southern Ocean (Indian Sector) during the ANTARES 1 cruise. In combination with solubility data reported by Van Cappellen and Qiu (1997a), a process model representing the early diagenesis of silica was developed. In this model, a dependence with depth of the kinetic constant was introduced to allow the preservation of biogenic silica in sediment porewater undersaturated with respect to that phase. Using this steady-state model, it is proposed that a proportionality of the reactivity of the biogenic silica with its settling flux is necessary to explain the observed profiles. It is then shown using this model that the preservation of biogenic silica is not a linear function of the deposited flux. Using a modified version of this model containing an explicit term of reprecipitation, we hypothesize that reprecipitation alone cannot counterbalance dissolution and that its effect is certainly related to a decrease in either surface solubility or kinetics of dissolution.
Christophe Rabouille - One of the best experts on this subject based on the ideXlab platform.
-
recycling of organic matter in Antarctic sediments a transect through the polar front in the southern Ocean indian sector
Limnology and Oceanography, 1998Co-Authors: Christophe Rabouille, Jeanfrancois Gaillard, Paul Treguer, J C Relexans, Marie Anne VincendeauAbstract:Sediments from the Polar Front Zone were sampled in the Indian Sector of the Antarctic Ocean as part of the French JGOFS expedition Antares 1. The first porewater distributions of O2 and NO3= and organic carbon data in the solid phase in this part of the Ocean were used to model the recycling of organic matter in sediments. The data are described by a model containing two types of degradable organic matter with distinct reactivities. We estimate that the reactivity of the most labile organic carbon is very close to that of fresh organic matter with an average C : N ratio of 7. We estimate that particulate organic carbon fluxes deposited at the sediment-water interface range between 0.2 and 0.8 mol C m−l y−l, with two peaks near the Polar Front and the SubAntarctic Front. The flux 01 organic carbon deposited at the sediment-water interface is unusually high and represents ˜10–20% of estimated primary production. From these findings, we conclude that production in the pelagic zone of this region is strongly linked to deposition and recycling in the sediment.
-
biogenic silica recycling in surficial sediments across the polar front of the southern Ocean indian sector
Deep-sea Research Part Ii-topical Studies in Oceanography, 1997Co-Authors: Christophe Rabouille, Jeanfrancois Gaillard, Paul Treguer, Marie Anne VincendeauAbstract:Abstract The processes controlling preservation and recycling of particulate biogenic silica in superficial sediments must be understood before one uses biogenic silica as a proxy in paleoOceanographic studies, and in order to compute Oceanic mass balances for silica. In this respect, the Antarctic Ocean is certainly a key region due to its high productivity and export of biogenic silica. In order to quantify sedimentary fluxes and identify crucial processes that allow the preservation of biogenic silica, pore water and solid phase silica profiles were performed on sediment cores from the Southern Ocean (Indian Sector) during the ANTARES 1 cruise. In combination with solubility data reported by Van Cappellen and Qiu (1997a), a process model representing the early diagenesis of silica was developed. In this model, a dependence with depth of the kinetic constant was introduced to allow the preservation of biogenic silica in sediment porewater undersaturated with respect to that phase. Using this steady-state model, it is proposed that a proportionality of the reactivity of the biogenic silica with its settling flux is necessary to explain the observed profiles. It is then shown using this model that the preservation of biogenic silica is not a linear function of the deposited flux. Using a modified version of this model containing an explicit term of reprecipitation, we hypothesize that reprecipitation alone cannot counterbalance dissolution and that its effect is certainly related to a decrease in either surface solubility or kinetics of dissolution.
Yutaka Fukui - One of the best experts on this subject based on the ideXlab platform.
-
functional reduction of the southern minke whale balaenoptera acutorostrata testis during the feeding season
Marine Mammal Science, 2000Co-Authors: Toshihiro Mogoe, Hajime Ishikawa, Yutaka Fukui, Takatoshi Suzuki, Masatsugu Asada, Seiji OhsumiAbstract:Seasonal variation in reproductive activity in the male southern minke whales was investigated. The animals were killed and collected during the feeding season (December-March) in the Antarctic Ocean in the eastern part of Area III (35°E-70°E, south of 60°S) and Area IV (70°E-130°E, south of 60°S). Blood samples, testes, epididymides, and vasa deferentia were collected from 62 males, which had testes weighing over 400 g each. Changes in testicular morphology and plasma testosterone, estradiol-17β and LH concentrations measured by enzyme immunoassay were investigated. Reduction of testicular function associated with different capture periods was found in the summer season. From December to March, body length and body weight remained steady, but decreases in testicular weight, epididymal weight, and testicular volume were found in February. During the same period, plasma testosterone concentration also declined. A significant decrease in the number of germ cells continued during the period of feeding season. An increase in area of seminiferous tubule tended to proceed in a number of germ cells. These changes reflected the percentage of spermatozoa in the vasa deferentia; in particular, motile spermatozoa were observed in December. Based on morphological observation, spermatogenesis had also declined. These results indicate regulation of testicular function by testosterone, as in terrestrial mammals. A gradual decrease of testicular function occurred during December-January.
-
in vitro fertilization of in vitro matured minke whale balaenoptera acutorostrata follicular oocytes
Marine Mammal Science, 1997Co-Authors: Yutaka Fukui, Hajime Ishikawa, Toshihiro Mogoe, Seiji OhsumiAbstract:In vitro fertilization of follicular oocytes harvested from ovaries and matured in vitro was attempted for 55 minke whales (Balaenoptera acutorostrata) captured for Japanese research purposes in the Antarctic Ocean during the period from November 1995 to March 1996. In Experiment 1, effects of culture duration (96 h or 120 h) on maturation of follicular oocytes and addition of caffeine (5 mM) and/or heparin (100 pg/ml) on sperm penetration and pro-nuclear formation were investigated. Spermatozoa recovered from the vasa deferentia of four mature males were diluted (5-fold) and frozen at - 80°C. The post-thawed and pooled spermatozoa were used for in vitro insemination. A higher (P < 0.05) proportion of the oocytes cultured for 120 h (34.2% of 260) progressed beyond the second metaphase stage than of the oocytes cultured for 96 h (26.0% of 262). For the matured oocytes, higher rates of penetration (P < 0.05) and pronuclear formation (P < 0.01) were obtained in the oocytes cultured for 120 h (55.1% and 40.4%) than in those cultured for 96 h (32.4 % and 20.6%). Addition of caffeine and heparin did not show a significant effect. In Experiment 2, follicular oocytes matured for 120 h and then inseminated were cultured to examine the subsequent development in two culture systems (with and without co-cultured cumulus cells). Of 448 inseminated oocytes, cleaved embryos (2–16 cells) were observed with (5.8%) and without (4.9%) co-cultured systems. No cleavage was observed in 54 ova without insemination. These results indicate that in vitro fertilization of minke whale in vitro matured follicular oocytes with cryopreserved spermatozoa is possible, yielding cleaved embryos.
Kim Suam - One of the best experts on this subject based on the ideXlab platform.
-
biomass and distribution of Antarctic krill euphausia superba in the northern part of the south shetland islands Antarctic Ocean
Korean Journal of Fisheries and Aquatic Sciences, 1999Co-Authors: Kang Donhyug, Hwang Doojin, Kim SuamAbstract:To estimate biomass and distribution of the Antarctic krill (Euphausia superba), hydroacoustic survey was conducted on board of R/V Yuzhmorgeologiya, which was chartered by Korea Antarctic Research Program (KARP) group from 18 to 21 December 1998, in the northern part of the South Shetland Islands, Antarctic Ocean, The scientific echo sounder (towing body type) used was EK- 500 (SIMRAD, Norway) with echo integrator (BI-500) at 38 kHz frequency and recorded mean backscattering cross-section coefficient (SA) per 1 of sea surface. Also, Bongo net sampling was carried out to determine the size of krill and CTD (Conductivity, Temperature and Depth) casting to understand physical structure. Water column was divided into 5 layers (2265 m, 65115 m, l1565 m, 165215 m and 215315 m) to know vertical distribution of krill biomass. The standard length of krill collected was between 30 mm and 51 mm, and adult krill had single mode (41 mm). Maximum horizontal length of krill patch was about 35 nautical mile and vertical thickness was about 275 m. High density of krill was appeared in frontal area between Circumpolar Deep Water (>) and very low temperature water mass () that originate from Weddell Sea. According to the results calculated using target strength equation, krill density was totally higher in continental slope and open water areas than in coastal area. In the study area, krill seems to distribute in depth; density was low at first layer () and higher at fourth layer (). The estimated krill biomass at total survey area and water column was about 2.77 million metric ion () and coefficient of valiance ( CV, ) was 19.92. The proportions and biomass of krill biomass at each layer were as follows; layer 1 (, 0.31 million metric ton, CV=16.24), layer 2 (, 0.37 million metric ton, CV=34.91), layer 3 (, 0.66 million metric ton, CV=41.5), layer 4 (, 0.74 million metric ton, CV=27.84) and layer 5 (, 0.69 million metric ton, CV= 26.83).