Shun-ei Ichimura

Measurement of photosynthetic production of a marine phytoplankton population using a stable 13C isotope

The use of stable isotope of carbon, 13C, for the determination of the photosynthetic rate of a marine phytoplankton population was examined. Particular concern was paid to the effects of non-phytoplanktonic organic carbon and the enrichment of inorganic carbon on the estimation of the photosynthetic rate. Photosynthetic rates determined by the 13C method showed a remarkable agreement with those determined by the 14C method. Insitu determinations of photosynthetic rate were made in three different water types: open ocean, coastal and neritic waters, which included oligo- and mesotrophic waters, by using the 13C method established.

Upwelling plumes in sagami bay and adjacent water around the Izu Islands, Japan

Water plumes, 20 km long or less, identified by low temperature, high salinity and high nutrient concentrations, were observed on the eastern side of Izu Islands where the Kuroshio Current or its branch flowed eastward. The T-S diagrams and the vertical profiles of oceanographic variables indicated that the water plumes resulted from the upwelling of subsurface water. A newly formed plume, characterized by a sharp temperature front and high nutrient concentrations, contained less chlorophyll than did old plumes. It is suggested that the upwelling plumes are maintained for a period long enough to allow luxuriant growth of phytoplankton.

Abundance and life history ofNeomysis intermedia Czerniawsky in Lake Kasumigaura

AbstractWeekly observations ofNeomysis intermedia in Lake Kasumigaura showed two major peaks in abundance during spring and autumn (more than 104 individuals m−2) and minimum levels in summer and winter (less than 103 individuals m−2). Their increase in abundance followed a high egg ratio, suggesting that the increase in abundance was caused by a high reproductive rate. Major contributors to mysid population decreases include fish predation and commercial fisheries, and possible horizontal migration of the mysids. N. intermedia showed two types of life history in the lake. One type (overwintering generation) has a life span of about 6–7 months and produces about 27 eggs per brood. Another, appearing from spring to autumn, matures in 3–6 weeks at a smaller size, and produces 12 eggs per brood. The reproductive season ofN. intermedia was continuous from March through November.

Selective transmission of light in the ocean waters and its relation to phytoplankton photosynthesis

Occurrence of the depth differences in pigment composition and photosynthetic properties of marine phytoplankton were examined in relation to the spectral changes of light with depth. Phytoplankton were taken from various depths in the northwestern North Pacific, and their absorption spectra were determined with intact cells and in 90% acetone extract. The photosynthetic activities of phytoplankton were concurrently measured under blue, green, red and white light. The difference in absorption spectra for the surface and deeper samples was considerably small, indicating that the prevailing green or blue light in the deeper layers may have little significance for depth-variations of the pigment composition in marine phytoplankton. The depth differentiation in the shape of the light-photosynthesis curve was marked in a well stratified water column but no active response of deeper phytoplankton to green light could be confirmed. The photosynthetic efficiencies of phytoplankton for blue and green light were approximately 105–115 % and 80–90 % of white light, respectively, irrespective of sampling depth.

Dynamics of dissolved oxygen during algal bloom in Lake Kasumigaura, Japan

Abstract Dynamics of dissolved oxygen during an algal bloom were studied in Lake Kasumigaura. Great amounts of oxygen arose from photosynthesis, and the concentration of dissolved oxygen reached 190% of saturation at 12 h. The majority of the dissolved oxygen produced was liberated into the atmosphere or consumed by microorganisms. Only minor fractions were transported into the dysphotic zone due to the low eddy diffusion coefficient in deeper waters of the euphotic zone.

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.

Shade and chromatic adaptation of phytoplankton photosynthesis in a thermally stratified sea

Spectral absorption of photosynthetically active radiation (PAR) by natural phytoplankton and photosynthetic rates under blue, green, red and white lights with various intensities were determined in the thermally stratified open sea off Shikoku Island, Japan, between 9 June and 8 July 1982. Two characteristic phytoplankton populations, sun- and shade-types, were recognized above and below the 10% light depth, respectively, from photosynthetic responses. The shade-type is characterized by a small photosynthesis maximum at low optimum light intensity, severe photo-inhibition and steep initial slope of photosynthetic rate in comparison with the sun-type. Photosynthetic rates of both types were highest in blue light among three other lights at a given intensity; this “effective use of blue light” is expected to be advantageous mostly for the shade-type because the blue light field predominated at greater depths. Together with these photosynthetic responses and the blue light environment, the subsurface population was expected to maintain effective utilization of light in its habitat. An increase of cell pigment concentration in a low-light environment presumably induced phytoplankton to harvest light energy effectively. Quantum yields determined varied between 0.02 to 0.12 mole C E-1, although no obvious difference was noticed in different light sources and growth habitats.

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.

Temperature dependence of filament length of Anabaena spiroides Klebahn var. crassa Lemm.

Temperature dependence of filament length ofAnabaena spiroides Klebahn var.crassa Lemm. was examined for a strain isolated from Lake Kasumigaura, Japan. The length of the algal filaments is shown to have good correspondence with the thermal master reaction of cell multiplication.

Primary productivity in coastal water adjacent to the Kuroshio off Shimoda

The primary productivity in coastal water adjacent to the Kuroshio off Shimoda was measured as part of the International Biological Program. The total amount of chlorophylla in the euphotic zone varied widely from 20 mg/m2 to 60 mg/m2 throughout the year and the maximum values were measured in early summer. These values were higher than those in the Kuroshio but agreed with those in the Oyashio. Vertical differentiation of photosynthetic characteristics was well developed and it was strongly related to the stratification of the water column. The light-saturated photosynthetic rate of surface phytoplankton varied from 5.8 mg C/(mg chl.h) in May to 2.0 mg C/(mg chl.h) in January. These rates were higher than those in the Kuroshio. The daily primary production was estimated by the chlorophyll method. Highest value was 0.5–1.5 g C/(m2day) in early summer and the lowest was 0.2 g C/(m2day) in winter. The primary productivity in the coastal water studied accorded fairly well with that in the Oyashio.