Yukuya Yamaguchi

A phytoplankton absorption-based primary productivity model for remote sensing in the Southern Ocean

Recent global environmental changes such as an increase in sea surface temperature (SST) are likely to impact primary productivity of phytoplankton in the Southern Ocean. However, models to estimate net primary production using satellite data use SST and uncertain estimation of chlorophyll a (chl-a) concentration. A primary productivity model for satellite ocean color data from the Southern Ocean, which is based on the light absorption coefficient of phytoplankton to reduce uncertainties of sea surface chl-a estimations and bias in optimal values of chl-a normalized productivity derived from SST, has been developed. The new model was able to estimate net primary productivity in the water column (PPeu) without dependency on temperature when in the range of −2 to 25°C, and it explained 51% of the observed variability in PPeu with a root mean square error (RMSE) of 0.15. Application of the model revealed that the SST dependent model has overestimated PPeu in warmer waters around the Subtropical Front, and underestimated PPeu in colder waters poleward of the Sub-Antarctic Front. This absorption-based primary productivity model contributes to a study of the relationship among spatio-temporal variations in the physical environment, and biogeochemical cycles in the Southern Ocean.

Photo-inhibition of phytoplankton photosynthesis as a function of exposure time

AbstractThe photo-inhibition of phytoplankton photosynthesis at higher intensities was examined with a cultured marine diatom,Phaeodactylum tricornutum, and natural samples. The question was to determine whether photo-inhibition results from excretion of photosynthetic products from cell or from an actual decrease in photosynthetic rate. P. tricornutum cultured at 15 klux showed very little photo-inhibition up to 70 klux, and, in the sample cultured at 1 klux, most marked photo-inhibition was observed in 3 hours experiment. Extracellular release was less than 30% of particulate fixation, and did not show any extreme increase to supplement photosynthesis depression at higher light intensities. When the photosynthesis was measured during 10 minutes, both samples showed no photo-inhibition. The photosynthesis by low light sample lost the linearity of time-course with prolonged exposure at high light intensity. Observed photo-inhibition, therefore, we explained with the actual decrease in photosynthetic rate. Similar photo-inhibition could be seen in marine phytoplankton samples concentrated by filtration.

The distribution of chlorophylla, protein, RNA and DNA in the North Pacific Ocean

Chla, protein, RNA and DNA were measured in 400 samples taken from the surface down to 5,000 m at 27 oceanographical stations in the North Pacific Ocean. Two section diagrams of these cellular constituents were given along 155°E and 155°W meridians, and several vertical profiles of the four constituents were also given at some stations near Japan. The average concentration ranges of Chla, protein, RNA and DNA obtained in this study area were 0.025–0.862, 11.4–88.1, 1.36–35.3 and 0.13–5.24μg/l, respectively. Chla was distributed mostly in the photic zone as we would expect. However protein, RNA were in high concentrations within the photic zone and sometimes extremely high concentrations in the deep aphotic zone.

Seasonal changes of organic carbon and nitrogen production by phytoplankton in the estuary of River Tamagawa

Abstract Seasonal changes of organic carbon and nitrogen production were investigated at a station in the estuary of River Tamagawa in Tokyo Bay. Standing stock of phytoplankton expressed as a concentration of chlorophyll α and their photosynthetic activities fluctuated significantly with sampling periods. Based on the data obtained in 1988 and 1989, the levels of annual production of organic carbon and nitrogen by phytoplankton community in this estuary were estimated to be 1890 gC m −2 yr −1 and 281 gN m −2 yr −1 , respectively.

Extracellular release of photosynthetic products by a pelagic blue-green alga,Trichodesmium thiebautii

Extracellular release of photosynthetic products by a pelagic blue-green alga,Trichodesmium thiebautii, was scrutinized in relation to pre-treatments in14C-method for measuring the primary productivity.The extracellular release increased markedly by the pre-treatments with such strong fixative solutions as formaldehyde and mercuric chloride. In such a case, the amount of extracellular fraction reached even almost 78 % of the total photosynthates. The extracellular release of photosynthates was dependent both on light intensity and on physiological state of algal cells. When photosynthesis was terminated by a fixative, the extracellular release was noticed even just after the fixation, and it increased with time. Thus, it appears to be difficult to deduce the real photosynthetic production capacity from the amount of cellular fraction only.The amount of extracellular fraction for unfixed samples filtered immediately after the incubation was less than 8 % of the total photosynthetic products inT. thiebautii. This value is nearly comparable to the amount of excretion reported in many cultured algae.

Microbial biomass in the Eutrophic Bay of Shimoda as compared by estimations of several biomass parameters

Microbial biomass in seawater of Shimoda Bay was assessed using some biomass parameters, such as ATP, DNA, RNA, protein, chlorophylla, and bacterial number and every estimate is in the same order. The estimates based on the amounts of ATP, DNA and RNA showed good correlation.

Bacteria on petroleum globules in the Philippine sea in January, 1973

About 106 of total bacteria (direct microscopic count) or heterotrophic bacteria (colony count with Medium 2216E) and about 104 of petroleumlytic bacteria (oil-oxidizing bacteria) were enumerated per square centimeter of the surface of petroleum globules suspended in the topmost 10 meters of water from a station (22°00.2′N, 125°51.9′E) in the western North Pacific central water, where about 107 of total bacteria, about 103 of heterotrophic bacteria and about 10 of petroleumlytic bacteria were enumerated per liter of seawater.

Dynamic status of primary production in lake yunoko, a small eutrophic subalpine lake in central Japan

Investigation was made of the primary productivity of Lake Yunoko. The concentrations of PO4-P and NH3-N were highest in summer. The total amount of chlorophylla in the entire water column varied from 45 mg/m2 to 405 mg/m2 during the year with the maximum values occurring in late spring and in December. These values are very high compared with those reported for other lakes in the same district. The standing crop of phytoplankton as organic carbon was approximately 50∼70% of the total particulate organic carbon in the lake with values as high as 80∼90% being obtained in the spring and autumn. The rate of phytosynthesis under saturated light conditions was 3.7 mg C/mg chla/hr in the case of phytoplankton of the sun type and 1.2∼1.6 mg C/mg chla/hr in those of the shade type. The daily gross primary production in the lake varied from a low of 134 mg C/m2 to a high of 1,003 mg C/m2 during the year, the mean value being 372 mg C/m2. The total amount of daily microbial respiration varied from 177 mg C/m2 in winter to 1,476 mg C/m2 in summer. Thus, the daily balance of production and consumption of organic matter in the lake itself was concluded to be negative. The main factor contributing to the rectification of this imbalance of material budget seems to be the leaf litter coming from the forest surrounding the lake. In conclusion, Lake Yunoko is a very productive and at the same time, fairly heterotrophic lake.

Limnogicai Features of Lake Yogo-ko in the Summer of 1969

Physico-chemical and biological properties of Lake Yogo-ko were investigated in the summer of 1969. A weak thermal stratification was observed with a gradient of 0.5° per meter in the depth of 4-8m. In late summer, dissolved oxygen disappeared in the layer near bottom. The concentration of NH3-N varied from 48 μg/l in early summer to 2 μg/l in late summer, whereas PO4-P was present close on the same concentration (15-23 μg/l). Melosira italica and Melosira granulata were dominant during June and August, and Ceratium hirundinella in September. The amount of chlorophyll-a in the whole water column varied in a range of 40 mg/m2 to 48 mg/m2 and the daily net primary production ranged from 0.75 g CO2/m2/day to 0.88 g CO2/m2/day during the summer. Upon surveying the data of the last thirty years, Lake Yogo-ko has progressed in eutrophication rapidly in the last decade, and it is moderately eutrophic at present.