Shigeru Montani

Long-chain alkenones and alkyl alkenoates in the coastal and pelagic sediments of the northwest North Pacific, with special reference to the reconstruction of Emiliania huxleyi and Gephyrocapsa oceanica ratios

Abstract Long-chain (n C37ue5f8C39) alkenones and (n C37ue5f8C38) alkyl alkenoates in marine sediments are derived mainly from two marine coccolithophorids, Emiliania huxleyi and Gephyrocapsa oceanica. Laboratory cultured strains of E. huxleyi (strain EH2) and G. oceanica (strain GO1), isolated from the Great Barrier Reef and Mutsu Bay in northern Japan (41°N, 141°E), respectively, were cultured at 10°C, 15°C, 20°C, 22°C, 25°C, 28°C and analyzed for C37 to C39 alkenones, C36 methyl alkenoate (FAME) and C36 ethyl alkenoate (FAEE). Results obtained indicated significant differences in the alkenone and alkyl alkenoate profiles between these two algal species. The ratios of FAEE to C37 alkenones ( EE K37 ) and C38 alkenones ( EE K38 ) in G. oceanica were higher than those in E. huxleyi and, for both algal species, these ratios showed strong negative nonlinear exponential correlations when plotted against the unsaturation index of C37 alkenones (Uk·37). Using fitted equations for these relationships, the relative abundance of E. huxleyi and G. oceanica in the sediment samples from the northwest North Pacific and the coastal and inland waters of Japan were estimated and compared with direct microscopic determinations. E. huxleyi comprised more than 80% of the sedimentary coccolith assemblage in the open ocean, whereas G. oceanica was exclusively dominant in the inland waters. These results almost agreed with microscopic counts of these coccoliths occurring in the sediment samples. In the light of these findings, we suggest that there is a possibility that the relative abundance of E. huxleyi and G. oceanica in sediments may be estimated using nonlinear exponential calibrations based on EE K37 to Uk·37 and EE K38 to Uk·37 regressions.

The Effect of a Tidal Cycle on the Dynamics of Nutrients in a Tidal Estuary in the Seto Inland Sea, Japan

A 24 hour time series survey was carried out during a spring tide (tidal range ca.2 m) of May 1995 on a tidal estuary in the Seto Inland Sea, Japan, in the context of an integrated program planned to quantify the dynamics of biophilic elements (carbon, nitrogen and phosphorus) and the roles played by the macrobenthos on the processes. Three stations were set along a transect line of about 1.4 km, which linked the river to the rear to the innermost part of the subtidal zone. Every hour, at each station, measurements were made of surface water temperature, salinity and dissolved oxygen concentration, and surface water was collected for the determination of nutrients [NH4+−N, (NO3−+NO2−)−N, PO43−−P and Si (OH)4−Si]. During the ebb flow, riverine input of silicate and nitrate+nitrite significantly increased the concentrations of both the intertidal and the subtidal stations. Conversely, during the high tide, river nutrient concentrations were lowered by the mixing of fresh water with sea water. As a result, best (inverse) correlations were found at the river station for salinity against silicate (y=-2.9 Sal.+110.7,r2=0.879) and nitrate+nitrite (y=-1.3 Sal.+48.4,r2=0.796). In contrast, ammonium nitrogen concentrations were higher at intermediate salinities. Indeed, no significant correlation was found between salinity and ammonium. The effect of the macrobenthos, which is abundant on the intertidal flat, is discussed as a biological component that influences the processes of nutrient regeneration within the estuary. The effect of the tidal amplitude is an important one in determining the extent of the variations in nutrient concentrations at all three stations, which were stronger between the lower low tide and the higher high tide.

Efficiency of the decomposition of organic matter, loaded on the sediment, as a result of the biological activity of Capitella sp. I

Abstract Over the past three decades, fish farming in net pens has been extensively developed in Japanese coastal seas. Recently, however, many fish farms have suffered from organic pollution of the bottom environment, due to the vast discharge of organic matter from the fish farms themselves. During the summer, the bottom water in organically polluted areas is apt to be anoxic. High levels of hydrogen sulphide are often produced in the organically polluted sediment. We have attempted to treat the organically polluted sediment by exploiting the biological activities of a deposit-feeding polychaete, Capitella sp. I. In experiments in the laboratory, the size of colonies of this species increased very rapidly, and the organic matter that was loaded on the sediment was very efficiently decomposed. The proliferating colonies also promoted the oxidation of the reduced sulphides in the sediment. The results of this study indicate that dense patches of more than 59 000 individuals m −2 have the potential to exhaust the organic matter loaded on the seabed at a depth of 10 m below the net pens used for fish culture. The ability of a Capitella population to decompose organic matter may be applicable to the treatment of organically polluted sediment that accumulates below the fish farms.

Modification of chemical characteristics of organically enriched sediment by Capitella sp. I

Abstract The influence of biological activities of a deposit feeding polychaete, Capitella sp. I to the chemical characteristics of the organically enriched sediment was examined in the laboratory experiments. The laboratory colonies of Capitella increased very rapidly in the organically enriched sediment of the culturing boxes. In the process of the rapid population growth, the biological activities of the worms apparently promoted the decomposition of organic matter in the sediment, and decreased the levels of acid volatile sulphide (AVS) in the sediment. The results of the present study indicate that the effect of Capitella imposed on the sediment may be a method of biological treatment of the organically polluted sediment.

Early diagenesis of amino acids in Okhotsk Sea sediments

Abstract Amino acids, organic carbon, and total nitrogen were determined in five sediment cores from the Okhotsk Sea. The factors controlling the early diagenesis of organic nitrogen compounds are discussed. The amino acid contents were in the range of 2 to 8 mg g −1 of dry sediment at the surface. A rapid linear decrease from the surface to 1.5 m was observed in all five cores. The amounts of amino acids in the subsurface layer were 37.6±8.1% at 1 m and 27.8±14.5% at 1.5 m of those at the surface. Below 1.5 m the amino acid contents remained nearly constant at about 25%. The ratio of amino acid nitrogen to total nitrogen was 24±9% in the surface, 12.5±3.5% at 1 m, 11.0±6% at 1.5 m, and 11.2±2.5% at 1.5 to 3.0 m. The profiles of amino acid groups showed that the fraction of acidic amino acids decreased with depth and basic amino acids were constant or increased slightly with depth. Laboratory decomposition experiments under conditions of high pressure and temperature suggested that the acidic and aromatic amino acids were predominantly decomposed, whereas neutral and basic amino acids were maintained at a constant value. It is presumed that the relative changes of amino acid composition depend primarily on preferential hydrolyses at acidic or aromatic amino acid sites and deamination during the diagenesis.

Standing stock and production rate of phytoplankton and a red tide outbreak in a heavily eutrophic embayment, Dokai Bay, Japan.

The seasonal variation of phytoplankton biomass and primary productivity in a heavily eutrophic embayment, Dokai Bay, Japan, was determined. Dokai Bay was characterized by high phytoplankton biomass and productivity during summer and low phytoplankton biomass and productivity during other seasons. The results suggested that phytoplankton growth was limited by only irradiance and water temperature under the high nutrient concentrations available for phytoplankton growth in the entire year. Moreover, in spite of sufficient nutrient for phytoplankton growth in the entire year, a red tide occurred only in the summer period in this bay. Our results suggested that a red tide occurred by the high phytoplankton growth rate in the summer season, but in other periods surface phytoplankton was flushed out of the bay before forming the red tide, because phytoplankton growth rate was low and could not form the red tide due to low irradiance and low water temperature.

Semidiurnal Dynamics of Salinity, Nutrients and Suspended Particulate Matter in an Estuary in the Seto Inland Sea, Japan, during a Spring Tide Cycle

The physical and chemical variability of the water column at subtidal station of an estuary in the Seto Inland Sea, Japan, was studied over a 24-hour period during a spring tide (tidal range ca. 2 m) in May 1995. Surface water and several depths through the water column were monitored every one and two hours, respectively. At each occasion, water temperature, salinity and dissolved oxygen concentration were measured and water samples were collected for the determination of nutrients and suspended particulate matter (SPM). Disruptive changes in the physical and chemical characteristics of the water was produced by the tidal cycle and the mixing of water masses of different origin. These changes were highly significant both spatially and temporally, yet with varying effects on physical parameters, nutrients and the different components of SPM. Significant differences in nutrient concentrations were also observed when the data-set was divided into ebb and flood components, irrespective of the depth. Nitrate and nitrite rose to 1.8 times higher during the flood. Spatial differences of SPM were less marked than those of nutrients, only particulate organic carbon (POC) being significantly higher at the surface than in the intermediate and the lower layer. Both POC and pheopigment concentrations increased markedly through the water column, being highest shortly before the lower low tide. In contrast, suspended solid (SS) content increased sharply after the lower low tide (>40 mg l−1) and this coincided with a marked decrease of the C/SS content (<20 mg g−1). The lagtime between POC and SS tidal transport was caused by particle resuspension from the exposed intertidal sediments as the tidal level rose, and particle transport selection in relation to the tidal state.

CHANGES IN CELL CHEMICAL COMPOSITION DURING THE LIFE CYCLE OF SCRIPPSIELLA TROCHOIDEA (DINOPHYCEAE)1

The cellular content of carbon, nitrogen, amino acids, polysaccharides, phosphorus and adenosine trtphosphate (ATP) was determined at several stages during the life cycle of the dinoflagellate Scrippsiella trochoidea (Stein) Loeblich. Carbon per cell decreased slightly between exponential and stationary phase growth in vegetative cells whereas nitrogen per cell did not change. Both of these cellular components increased markedly on encystment and then decreased to vegetative cell levels during dormancy and germination. C/N ratios increased gradually during cyst dormancy and activation, reflecting a more rapid decrease in N than in C pools, even though both decreased through time. Amino acid composition was relatively constant during the vegetative cell stages; glutamic acid was the dominant component. Arginine was notably higher in cysts than in vegetative cells but decreased significantly during germination, suggesting a role in nitrogen storage. The ratio of neutral ammo acids to total ammo acids (NAA/TAA) decreased as cysts were formed and then gradually increased during storage and germination. The ratio of basic ammo acids to total ammo acids (BAA/TAA) changed in the opposite direction of NAA/TAA, whereas the ratio of acidic acids to total amino adds (AAA/TAA) was generally invariant. Ammo acid pools were not static during the resting slate in the cysts: there was degradation or biosynthesis of certain, but not all, classes of these compounds. The monosacchande composition of cold and hot water extracted polysaccharides was quite different between cells and cysts. A high percentage of glucose in cysts suggests that the storage carbohydrate is probably in the form of glucan. Total cellular phosphorus was higher in all cyst stages than in vegetative cells. However, ATP‐cell−1 decreased as vegetative cells entered stationary phase and encysted, and continued to decrease in cysts during dark cold storage. ATP increased only as the cysts were activated at warm temperatures in the light and began to germinate. The above data demonstrate that dormancy and quiescence are not periods of inactive metabolism but instead are times when numerous biochemical transformations are occurring that permit prolonged survival in a resting state.

Impacts of Oxygen-Deficient Water on the Macrobenthic Fauna of Dokai Bay and on Adjacent Intertidal Flats, in Kitakyushu, Japan

Abstract Dokai Bay is surrounded by the city of Kitakyushu, Japan. We assessed the chemical conditions of its waters and sediments, and carried out quantitative samplings of the macrobenthic fauna of the bay and on adjacent intertidal flats from 1992 to 1993. Large amounts of organic matter were deposited on the floor of the bay and intertidal flats due to eutrophication, and resulted in the occurrence of oxygen-deficient water from the bottom to the middle layer during the summer. On the tidal flats, the sediments were kept oxygenated and accessible to benthic animals throughout the year. However, the macrobenthos declined markedly in summer. The oxygen-deficient water of the bay seemed to temporarily upwell onto the intertidal flats causing a catastrophic environmental disturbance. Following this, only a few polychaete species survived, in extremely low densities.

Molecular Analysis of Ribosomal RNA Gene of Red Tide Algae Obtained from the Seto Inland Sea

Eleven clones from five species of the planktonic microalgae, (Chattonella antiqua, Chattonella marina, Heterosigma akashiwo, Alexandrium catenella, and Scrippsiella trochoidea), which were collected from the Seto Inland Sea in Japan and from Thailand, were subjected to nucleotide sequence analysis of the D1/D2 domain of the large subunit (LSU) of their ribosomal RNA genes. After amplification by polymerase chain reaction using degenerated primers, whole-nucleotide sequences for the D1/D2 domains of the LSU rRNA gene of 11 microalgae were analyzed. Phylogenic tree analysis using these nucleotide sequences showed each species located in a cluster corresponding to its morphological classification. The nucleotide sequence data for Chattonella spp. suggest that multiple clones of both Chattonella antiqua and Chattonella marina are present in the Seto Inland Sea and that red tide blooms of Chattonella spp. in different years may have contained different clones.