Nobuhiko Handa

Production and export of particulate fatty acids, carbohydrates and combined amino acids in the euphotic zone

Abstract The dynamics of particulate organic matter (POM) in the euphotic zone were evaluated at the molecular level by the combination of two methods, 13 C-labeling of photosynthetic products and sediment trap collection of sinking particles, in Sagami Bay, Japan. Determinations of the fatty acids, carbohydrates and combined amino acids of photosynthetic products and POM sinking out of the euphotic zone enabled us to calculate the biochemical compound-based export efficiency (specific-compound e ratio). Carbohydrates and combined amino acids were separated into two fractions, methanol/water-soluble and -insoluble (residual) fractions after organic solvent extraction for fatty acid determinations. The specific-compound e ratios of carbohydrates (0.25) and combined amino acids (0.27) in the residual fraction were similar to the ratio of bulk particulate organic carbon (bulk POC) (0.26), while the ratios of fatty acids, and carbohydrates and combined amino acids in the methanol/water fraction were lower at 0.080, 0.078 and 0.064, respectively. Based on the specific production rates and the specific sinking rates of biochemical compounds, it was concluded that the dynamics of biochemical constituents of POM in the euphotic zone differed as follows: (i) the dynamics of combined amino acids in the residual fraction was similar to that of bulk POC; (ii) carbohydrates in the residual fraction were actively produced and actively degraded in the euphotic zone and actively removed by sinking; and (iii) fatty acids, and carbohydrates and combined amino acids in the methanol/water fraction, were actively produced and actively degraded in the euphotic zone and less removed by sinking. Major fatty acids, and carbohydrates and combined amino acids in the methanol/water fraction, occur primarily as organic constituents of intact phytoplankton. The export efficiency of intact phytoplankton was less than 10% and the carbon biomass of intact phytoplankton was less than one-third of the POC sinking out of the euphotic zone.

Fatty Acid Composition of Sinking Particles in the Western North Pacific

Fatty acids were measured in sinking particles collected using a time-series sediment trap from the continental slope off Hokkaido, Japan from September 1988 to May 1989. The fatty acids were mainly composed of saturated ones. However, remarkable components of fatty acids were obtained in the sinking particles in September 1988 and April-May 1989. The sinking particles in September 1988 showed a high abundance of 9-octadecenoic acid (18:1 n-9), suggesting a contribution of zooplankton derived materials. On the other hand, the sinking particles in April-May 1989 had a large content of 7-hexadecenoic acid (16:1) and eicosapentaenoic acid (20:5), suggesting a sedimentation of diatom cells during a spring bloom. The low contents of long-chain fatty acids at the same periods indicated a relatively small contribution of terrestrial inputs to the mass fluxes, in comparison to other periods. High values of unsaturated fatty acids to saturated fatty acids ratios (UFA/SAFA ratios) were found in the sinking particles in deep water. During a spring bloom, the sinking particles of large mass flux can transport unsaturated fatty acids, which are one of the most labile compound classes, from surface to deep water. It suggested that sedimentation of intact cells of phytoplankton occurred in the coastal ocean during a spring bloom.

Effect of UV-B radiation on the pathways of carbon biosynthesis in marine phytoplankton and its implications for the marine ecosystem

The threat of enhaneed solar ultraviolet-B radiation (UVBR) on rhe aquatie environment resulting from reeeding levels of stratospherie ozone is now being pereeived as real (MADRONICH 1994). Alrhough evidenee in support o f this pereeption is overwhelming, efforts at exrrapolating rhese findings, to allow aeeurate and unambiguous predietions of the likely eonsequenees of UVBR o n the marine eeosystem, have been eonfounded with uneertainty (l<ARENTZ er al. 1994). The siruation demands that we systematieally investigate the effeets of UVBR o n various aspeets of aquatie biologieal proeesses, espeeially in areas that are of immediate relevanee to the aquatie food ehain and biogeoehemieal eycles. During the last few years we have been investigating ehanges in rhe patterns of earbon metabolism aeeompanying UVBR-mediated deereases in phytoplankton produetion (GOES er al. 1994, 1995, 1996). The motivation for these studies stemmed from the reeognition that rhe rates of synthesis of individual bioehemieal compounds, rather than bulk earbon produerion within phytoplankton, may provide important clues for assessing the impaets of enhaneed UVBR on rhe aquatie eeosystem. This eonrribution summarizes the results of this study and diseusses their implieations for the marine food ehain and biogeoehemieal proeesses in the sea.