Satoru Taguchi

Primary production and standing crop of phytoplankton along the ice-edge in the Weddell Sea

Chlorophyll a, phaepoigments, primary production, nannoplankton, inorganic nutrients, and physical measurements were made in the upper water column at 17 stations occupied in the Weddell Sea in February and March 1977. The most conspicuous feature is the marked contrast between the low standing crop and primary productivity of the northern and central regions, compared with the much more productive shelf waters at the head of the Weddell Sea. Chlorophyll a in the euphotic zone was 4.36 ± 1.75 mg m−2 for the former regions and 31.6 ± 9.5 mg m−2 for the southern stations. Production in the water columns of the southern stations (0.41 ± 0.23 g C m−2 day−1) was approximately four times that at the northern-central ones (0.104 ± 0.092 g C m−2 day−1). Based on plant carbon: chlorophyll a ratio of 30 ± 10 estimated in the present study, an average specific growth rate (μ) of 0.71 was calculated. The nutrient concentrations showed an inverse distribution compared with those of chlorophyll a and primary production; higher nutrient concentrations were recorded at the northern stations than at the southern waters. Phosphate: nitrate: silicate ratios in the water column suggested the importance of nitrate for phytoplankton production. A significant relationship (P < 0.001) between chlorophyll a concentration and day-zooplankton biomass and a significantly higher ratio (P < 0.06) of night-to-day catch of zooplankton in the northern-central regions than in the southern region were found. This suggests that zooplankton do not need to migrate vertically in the southern regions due to abundance of food supply, whereas in the northern-central regions zooplankton must migrate upwards during the night to consume available food produced through the photosynthetic process. The study demonstrates that water column stability, grazing, and proximity to land masses are the most significant factors controlling phytoplankton production in the Weddell Sea.

SILICATE DEFICIENCY AND LIPID SYNTHESIS OF MARINE DIATOMS

Lipid synthesis of three marine diatoms was studied with a 14CO2 incorporation technique in silicate limited batch cultures. Growth rates were independent of the silicate concentration but the cellular yields were proportional to the initial amount of silicate. At the beginning of the stationary growth phase, lipid synthesis rates per unit culture volume increased by 1.7 times for Chaetoceros gracilis, 3.1 times for Hantzschia sp., and 2.8 times for Cyclotella sp., respectively compared to those during the exponential growth phase. Lipid carbon accounted for as much as 57% of the carbon in C. gracilis, 71% in Hantzschia sp., and 65% in Cyclotella sp., respectively. Additional enrichment with silicate during stationary growth phase allowed the cultures to grow further. Lipid synthesis rates were reduced during the subsequent growth phase, and the growth rates themselves were dependent on the level of biomass achieved during the previous stationary phase. However, the cellular yields were similar and probably controlled by light.

Seasonal study of fecal pellets and discarded houses of Appendicularia in a subtropical inlet, Kaneohe Bay, Hawaii

Fecal pellets and discarded houses of Oikopleura longicauda Vogt were collected every week with sediment traps for a 13-month period in a subtropical inlet, Kaneohe Bay, Hawaii. The annual average fecal pellet production rate per animal was 243±105 pellets per day (95% confidence limits). The annual average house production rate per single O. longicauda was 5·3±3 houses day −1 . Each house contained 65±32 pellets. The annual average sedimentation rate of fecal pellets was 6·3±2×10 6 pellets m −2 day −1 (44% of total zooplankton pellets) or 2·0±1 cm 3 m −2 day −1 (66% of total zooplankton pellets). The annual average sedimentation rate of discarded houses was 8·9±3×10 4 houses m −2 day −1 . A field estimate of sinking velocity for discarded houses was 3·7±2 m day −1 , of which the variation seemed to be controlled by the chemical composition of suspended particulate matter ( P

Physiological characteristics and production of mixed layer and chlorophyll maximum phytoplankton populations in the Caribbean Sea and western Atlantic Ocean

Abstract Phytoplankton photosynthetic rates and relative and absolute growth rates were estimated using 14 C techniques at five stations in the Carribean Sea and two stations in the western Atlantic. Integral photosynthetic rates at the Caribbean stations averaged (±1 S.D.) 633 ± 77 mg C m −2 d −1 . Light-saturated growth rates were about 0.6 d −1 . Relative growth rates averaged 85% in the surface mixed layer and 93% in the lower euphotic zone. Uptake of 14 C at night accounted for 26% of the integral production at the Caribbean stations. The specific activity of Chl a carbon increased at night, and growth rates inferred from this increase were highly correlated with nocturnal 14 C uptake. Based on the Chl a carbon specific activity data, about 76% of the nocturnal 14 C uptake was attributed to phytoplankton. This uptake may have represented assimilation of labeled DOC excreted during the photoperiod. Over 80% of the Chl a in the chlorophyll maximum layers fell in the picoplankton size range. Incubation of these populations at higher irradiance levels revealed no indication of light adaptation over a 24 h period, a result consistent with recent studies of Synechococcus . Chlorophyll maximum populations occurred at about the 3% light level and were estimated to be growing with a doubling time of a little over 2 days. Estimated phytoplankton carbon concentrations were virtually identical in the mixed layers and chlorophyll maxima. The latter were therefore the result of adaptation of the phytoplankton to low irradiance levels and did not represent biomass maxima.

Sedimentation of newly produced particulate organic matter in a subtropical inlet, Kaneohe Bay, Hawaii

Sinking material was collected every week with sediment traps for a 13-month period in a subtropical inlet, Kaneohe Bay, Hawaii. A ratio method was applied to distinguish sedimentation from resuspension. No seasonality was observed in the sedimentation rate. An annual average of 73±6% of the total material trapped had been resuspended. The resuspension rate appeared to be controlled by wind speed (P

Vertical Distribution of Diverse Phytoplankton Communities in the Central Pacific

Southeast of Hawaii in the central Pacific, phytoplankton samples were taken on three transects. An average of over 20,500 cells/liter, including flagellates, was found for all depths counted, with diatoms, dinoflagellates, and coccolithophorids together accounting (in about equal numbers) for half that number. Coccolithophorids were dominant at some depths. The profile of cell numbers with depth showed a subsurface maximum with decreasing numbers at greater depths. The empty cell counts followed the same profile, with counts that were almost an order of magnitude smaller, probably indicating much recycling within the euphotic zone. Diversity indices revealed the complexity of the phytoplankton communities on these transects, and the Shannon Weaver index (H′) summed over all depths for each station appeared to approach an asymptote in most cases. Transect C (northeast of the other sites) showed a deeper mixed layer and greater diversity.

Phytoplankton Standing Crop and Primary Productivity in the Tropical Pacific

Phytoplankton standing crop and primary production were studied during the summer of 1975 and the winter of 1976, in the Deep Ocean Mining Environmental Study (DOMES) area between 5° – 20°N and 128° – 155°W. Chlorophyll a values (used as a measure of phytoplankton standing crop) averaged 0.063 mg/m3 in summer and 0.17 mg/m3 in winter. In the euphotic zone average values were 9.8 mg/m2 in the summer and 21 mg/m2 in the winter. The vertical distribution of chlorophyll a at the majority of the stations occupied was characterized by the presence of a subsurface chlorophyll maximum layer (CML). CML was found at a deeper depth (about 60 ± 24 m) in summer than in winter (about 54 ± 30 m). This layer occurred either at the middle or the bottom of the maximum density gradient (pycnocline) in summer whereas in winter it was found either at the top or the middle of the pycnocline. CML was also found to be closely associated with the distribution of the nutricline especially that of NO3-N.

Seasonal studies of the dinoflagellate Ceratium longipes (Bailey) Gran in the Bedford Basin, Canada

Abstract During an extensive bloom the subsurface Ceratium longipes (Bailey) Gran maximum layer was monitored with an attenuance meter and a particle counter in the Bedford Basin, Nova Scotia. This layer was controlled by the density-gradient. The cells absorbed mainly blue light in the region of 450–500 nm. Maximum cell number at the subsurface Ceratium maximum layer was 6.5 × 10 4 cells · 1 −1 , and single cell volume 6 × 10 4 μm 3 . Maximum total particle volume was 8.8 ppm and dominated by particles with diameters in the range 40–51 μm. The C. longipes made up 70% of total particle volume. A ratio by weight of organic carbon to nitrogen was 8, and the ratio of Ceratium carbon to chlorophyll a 84 ± 16. The growth rate was 0.56 doublings · day −1 , which is ≈ 40% of the empirical maximum at 7°C. The maximum quantum yield φm was 0.05 mole C · Einstein −1 . The effect of self-shading on φm was confirmed. The maximum light-saturated photosynthetic rate P m B , was 10.4 mg C · [mg Chl a ] −1 · h −1 or 0.07 mg C · [mg plant C ] −1 · h −1 . The maximum index of dark respiration R d B was − 0.25 mg C · [mg Chl a ] −1 · h −1 which corresponded to 2.5% of the P m B value. The physiological properties, i.e., φm, P m B and R d B of the dinoflagellate C . longipes are similar to diatoms even though their chemical properties are quite different.

Phytoplankton photosynthesis in the subsurface chlorophyll-maximum layer of the tropical North Pacific Ocean☆

Abstract Maximum quantum yield (φmB) and maximum photosynthetic rate (PmB) of light-saturation curves of phytoplankton photosynthesis were determined for nannoplankton ( 20 μm) from the subsurface chlorophyll-maximum layer at 14 stations in the tropical North Pacific Ocean in the spring of 1976. The maximum quantum yield (φ m B ± s.e. ) was significantly higher for nannoplankton (0.056 ± 0.006 moles CO2·Einstein−1 absorbed) than netplankton (0.039 ± 0.002 moles CO2·Einstein−1 absorbed). The importance of nannoplankton in the maximum photosynthetic rate (PmB) appears to be less consistent. At least 60% of the theoretical maximum quantum yield (0.12 moles CO2·Einstein−1 absorbed) was probably incorporated into the particulate fraction at the subsurface chlorophyll-maximum layer.