Takeo Hama

Spatial Variability in the Primary Productivity in the East China Sea and Its Adjacent Waters

Primary productivity in the East China Sea and its adjacent area was measured by the13C tracer method during winter, summer and fall in 1993 and 1994. The depth-integrated primary productivity in the Kuroshio Current ranged from 220 to 350 mgC m−2d−1, and showed little seasonal variability. High primary productivity (above 570 mgC m−2d−1) was measured at the center of the continental shelf throughout the observation period. The productivity at the station nearest to the Changjiang estuary exhibited a distinctive seasonal change from 68 to 1,500 mgC m−2d−1. Depth-integrated primary productivity was 2.7 times higher in the shelf area than the rates at the Kuroshio Current. High chlorophyll-a specific productivity (mgC mgChl.-a−2d−1) throughout the euphotic zone was mainly found in the shelf area rather than off-shelf area, probably due to higher nutrient availability and higher activity of phytoplankton at the subsurface layer in the shelf area.

13C Tracer Methodology in Microbial Ecology with Special Reference to Primary Production Processes in Aquatic Environments

Photosynthetic production by phytoplankton supplies organic material and energy to the aquatic food web consisting of bacteria, zooplankton, fish, water bird, whale, etc., and it may well be the most important step in the biological processes in aquatic environments. The estimation of primary productivity, thus, is essential to elucidating the dynamics of the microbial community and organic material. The importance of biological processes for the transfer of CO2 across the sea surface has recently been much discussed in relation to global changes (e.g., Berger et al., 1989; Longhurst, 1991). The dynamics of primary productivity, in particular, has a significant role in the global carbon cycle. Although there have been new approaches to assessing the dynamics, such as satellite imaging and time series sediment trapping, the direct measurement of the carbon uptake rate by phytoplankton photosynthesis can be regarded as the most reliable and basic estimate.

Production and turnover rates of fatty acids in marine particulate matter through phytoplankton photosynthesis

Abstract A combined 13 C and gas chromatography-mass spectrometry ( 13 C-GC-MS) method was applied for the determination of the fatty acid composition of photosynthetic products of phytoplankton. The accuracy of the estimation of 13 C abundance by GC-MS was ascertained by analyzing 13 C-enriched authentic specimens. The production rates of 17 fatty acids was determined in the regional upwelling and non-upwelling area around Hachijo Island, Japan. Although 14:0, 16:0 and 16:1 were the main components of the photosynthetically produced fatty acids at both stations, a marked difference in the proportion of 16:1 was found between the two stations, probably reflecting the difference in the dominant phytoplankton species. The ratio of unsaturated fatty acids to saturated fatty acids in the photosynthetic products was high in the upwelling area. The calculated turnover rate of each fatty acid through phytoplankton photosynthesis varied widely. Polyunsaturated fatty acids showed higher turnover rates, whereas low turnover rates were noticed in odd carbon number acids (iso 15:0, anteiso 15:0, 15:0 and 17:0) and 18:1 (n—7), which have been reported to originate from bacteria. The weighted average values of the turnover rates of all fatty acids determined in this study were 0.021 and 0.087 h −1 for the non-upwelling and the regional upwelling area, respectively.

Primary productivity and photosynthetic products around the Kuroshio warm-core ring

13C uptake experiments were carried out in the Kuroshio warm-core ring and adjacent waters during the cruise of R.V. Hakuho-Maru. The depth-integrated primary productivity at the warm-core center ranged from 840 to 1200 mgC m−2 day−1. These rates were higher than those obtained in the surrounding water and the warm streamer existing in the southern part of the warm-core ring, and lower than that in the cold Oyashio water. Production rates of 13 amino acids and eight monosaccharides at six stations were determined after hydrolysis of particulate matter by the 13C−GC−MS method. Protein and free amino acid (sum of 13 amino acids) carbon production rate accounted for 20–39% of organic carbon production at 10 m, whereas carbohydrate (sum of eight monosaccharides) was responsible for 11–21%. Composition of photosynthetic products and the spectrum of specific production rate (SPR) of organic compounds indicate that phytoplankton population in and around the warm-core ring was in a generally healthy state.

13C-GC-MS analysis of photosynthetic products of the phytoplankton population in the regional upwelling area around the Izu Island, Japan

Abstract Monosaccharide and amino acid composition of the photosynthetic products of the phytoplankton populations were determined by the combined 13 C and gas chromatography-mass spectrometry (GC-MS) method inside and outside of regional upwelling waters around the Izu Islands, Japan. The ratio of carbohydrate to protein in photosynthetic products was lower in the “maturing” upwelling waters, where high concentrations of nutrients were measured, than in the non-upwelling and the “aged” upwelling waters. Carbohydrate/protein ratios in photosynthetic products were closely correlated with glucose/carbohydrate ratios. The specific production rate (SPR) of glucose showed the highest value among compounds at almost all stations. The difference between SPR of glucose and those of other compounds was small in the “maturing” upwelling waters, whereas daytime SPR of glucose was over 10 times greater than those in other compounds in the non-upwelling and the “aged” upwelling waters. These results indicate that more “balanced” organic matter production occurred in the “maturing” waters than in the non-upwelling and the “aged” upwelling waters.

Photo synthetic products and nutrient availability in phytoplankton population from Gokasho Bay, Japan

Abstract Weekly changes in the photosynthetic products of natural phytoplankton population in Gokasho Bay, Japan, were determined by the combined 13 C and gas chromatography-mass spectrometry ( 13 C-GC-MS) method. Total organic carbon production rate determined by the daytime incubation (8.5 h) ranged from 7.5 to 47 μg C 1 −1 C h −1 , and from 2.3 to 17 μg C 1 −1 C h −1 in the day-nighttime incubation (21.5 h). Carbohydrate carbon production rate accounted for 15–81% of total organic carbon production rate in the daytime, and high values were obtained in the low inorganic nitrogen condition. In the low inorganic nitrogen period, glucose accounted for > 90% of carbohydrate production in the daytime. On the other hand, protein carbon formed 7.7–25 and 14–47% of total organic carbon production in the daytime and the day-nighttime, respectively. A high protein contribution was observed under the high nutrient concentration. These results strongly suggested that the distribution pattern of incorporated carbon was affected by nutrient availability.

Effect of nutrient conditions on the composition of photosynthetic products in the East China Sea and surrounding waters

Abstract Production rates of organic compounds such as fatty acids and monosaccharides, constituting lipids and carbohydrates, respectively, were determined by 13 C tracers and the gas chromatograph/mass spectrometry (GC/MS) method at five stations from the Kuroshio Current to the East China Sea during the summer of 1994. High phytoplankton biomass and primary productivity were found at the estuary of the Changjiang, and the photosynthetic products showed distinctive differences from those at other stations. A high contribution of 16:1(n-7) fatty acid (one of the marker compounds of diatoms) indicates the occurrence of a diatom bloom during our observation period. The ratio of low molecular weight (LMW) to high molecular weight (HMW) carbohydrates off the Changjiang was distinctly higher (1.3) than at the other four stations (0.007–0.091). This suggests that mono-/oligosaccharides did not polymerize to polysaccharides smoothly. The high contribution of glucose in the photosynthetic products at this station indicates that the phytoplankton population was in a nutrient-limited condition. In contrast, the low ratio of LMW to HMW carbohydrates and the lower contribution of glucose at other stations, including oligotrophic Kuroshio water, suggest that phytoplankton populations were not nutrient-limited.

Production and Turnover of Organic Compounds through Phytoplankton Photosynthesis

Primary production of phytoplankton in the surface layer of the ocean down to 200 m depth harvests the sunlight and converts light energy to chemical energy as chemical bonds of organic compounds. The life of marine heterotrophs including zooplankton, bacteria, fish and mammals depends on the organic compounds produced by phytoplankton. Through biological activity, organic compounds are partly decomposed, transformed and transported to the deep layer. The scale of primary productivity in the euphotic layer accordingly regulates the amount of biomass and accompanying material flux throughout the water column including the sediment.