Ken Furuya

Phytoplankton dynamics in the East China Sea in spring and summer as revealed by HPLC-derived pigment signatures

Abstract The community structure of phytoplankton was investigated from pigment composition in the East China Sea during an early spring bloom and a well-stratified summer season. Pigment concentration determined by high-performance liquid chromatography was interpreted using a matrix factorization program “CHEMTAX” (Mackey et al., 1996) to obtain the chlorophyll a biomass of phytoplankton groups at class level. There was a distinct horizontal heterogeneity in phytoplankton composition during spring. The spring bloom of diatoms was observed on the shelf, where weak stratification produced by overlying less saline surface water supported the bloom. In contrast, off the shelf where Kuroshio water prevailed, phytoplankton abundance was low and the community was composed mainly of prochlorophytes, chrysophytes, prymnesiophytes and chlorophytes. Patchy high concentrations of fucoxanthin were observed off the shelf, indicating transport of diatom-rich water from the shelf. In a clear contrast to the spring season, a “two-layer” distribution of phytoplankton prevailed both off and on the shelf in summer. There was a well-developed subsurface chlorophyll maximum at all the stations except near Changjiang estuary. In the upper mixed layer where nutrient salts were depleted, the phytoplankton community was characterized by high contribution of cyanobacteria followed by prochlorophytes, whereas in the chlorophyll maximum, prochlorophytes, chrysophytes and prymnesiophytes were most abundant. In both seasons, total amount of chlorophyll a was primarily determined by that of diatoms, and the chlorophyll a of procaryotes and eucaryotic flagellates did not exceed 0.4 and 1 μg l −1 , respectively, suggesting herbivorous control. Active grazing of macrozooplankton also was indicated in the diatom patch by the presence of degradation products of chlorophyll a.

Subsurface chlorophyll maximum in the tropical and subtropical western Pacific Ocean: Vertical profiles of phytoplankton biomass and its relationship with chlorophylla and particulate organic carbon

Vertical distribution of phytoplankton biomass in terms of carbon content (PC) and its relationship with chlorophylla and particulate organic carbon (POC) were examined together with phytoplankton growth rates in the tropical and subtropical western Pacific in 1979, where a prominent subsurface chlorophyll maximum (SCM) developed between 65 and 150 m. Fluorescence microscopy combined with image analysis was used for measurement of cell volume which was converted to PC. The SCM coincided consistently with subsurface maximum of PC, and the SCM primarily reflected in situ accumulation of phytoplankton biomass. The PC:chlorophylla ratio decreased with depth; the ratio was 1.8 times, on average, higher in populations at the SCM compared to those near the surface. This increase in relative cellular chlorophylla along with depth accentuated the magnitude of the SCM. The PC:POC ratio was substantially lower near the surface, 0.17 on average, and increased sharply around the SCM, with a mean value of 0.53. Thus suspended particles around SCM were richer in phytoplankton than those in the upper layers. A major part of PC was contributed by autotrophic eukaryotes both near the surface and at the SCM, and prokaryotic picoplankton comprised a relatively small proportion (6.3 to 14.9%) of PC. The high phytoplankton biomass around the SCM was suggested to be ascribed to in-situ growth of phytoplankton.

HPLC Determination of Phytoplankton Pigments Using N,N-Dimethylformamide

The suitability of N,N-dimethylformamide (DMF) as an extractant for the standard reverse-phase HPLC method was examined using algal cultures. Good pigment separations and recovery were achieved with 20% (volume %) addition of an ion-pairing solution in an injection. While slight amounts of degradation products of chlorophylla, i.e., chlorophyllidea, allomeric and epimeric forms, were produced, adequate attention to filtration and extraction prevents the formation of degradation products, confining them to an acceptable level. Because of its strong extractability, which expedites the extraction process, DMF is an efficient solvent for HPLC analysis of phytoplankton pigments.

Ocean urea fertilization for carbon credits poses high ecological risks

The proposed plan for enrichment of the Sulu Sea, Philippines, a region of rich marine biodiversity, with thousands of tonnes of urea in order to stimulate algal blooms and sequester carbon is flawed for multiple reasons. Urea is preferentially used as a nitrogen source by some cyanobacteria and dinoflagellates, many of which are neutrally or positively buoyant. Biological pumps to the deep sea are classically leaky, and the inefficient burial of new biomass makes the estimation of a net loss of carbon from the atmosphere questionable at best. The potential for growth of toxic dinoflagellates is also high, as many grow well on urea and some even increase their toxicity when grown on urea. Many toxic dinoflagellates form cysts which can settle to the sediment and germinate in subsequent years, forming new blooms even without further fertilization. If large-scale blooms do occur, it is likely that they will contribute to hypoxia in the bottom waters upon decomposition. Lastly, urea production requires fossil fuel usage, further limiting the potential for net carbon sequestration. The environmental and economic impacts are potentially great and need to be rigorously assessed.

Large‐scale impact of the island mass effect through nitrogen fixation in the western South Pacific Ocean

We describe a new mechanism for the island mass effect fueled by nitrogen fixation. The nitrogen fixation activities and δ15N of suspended particles in the surface water in the South Pacific were examined. Active nitrogen fixation and abundant Trichodesmium spp. were observed near islands in the western subtropical region, which was attributable to the material supplied by land runoff. High primary production was extensively centered around the islands and was characterized by low δ15N of suspended particles and a reduction in phosphate concentrations at the surface compared with the subtropical gyre and eastern equatorial upwelling. This suggested that Trichodesmium spp. were advected to areas remote from these islands, and consequently, the elevated primary production fueled by nitrogen fixation extended over a large area around them. Because the proposed island mass effect is triggered by a terrigenous nutrient supply, this ecosystem is potentially vulnerable to human activity on small islands.

Summer phytoplankton community structure and growth in a regional upwelling area off Hachijo Island, Japan

Abstract Phytoplankton community structure both in terms of taxonomic composition and size distribution, and growth were examined in a regional upwelling which occurred in a Kuroshio region in summer. Organic carbon abundance of diatoms was markedly enhanced by the upwelling and they accounted for 87% of the total phytoplankton carbon. Nitzschia pungens Grunow was numerically most prominent accompanied by Chaetoceros and Rhizosolenia species. On the other hand, only a small increase was observed in phytoplankton other than diatoms, which consisted of unicellular cyanobacteria, coccolithophorids, gymnodinoids, and so called monads and flagellates. Division rate of diatoms from the upwelled water was twice that of the other forms. This difference in growth response among phytoplankton groups resulted in a shift of community structure to dominance of diatoms from that of the other forms. The time needed for this shift was estimated to be at least ≈ 3 days.

In-Water Algorithms for ADEOS/OCTS

AbstractIn-water algorithms for OCTS standard products were developed using in situ data and installed for operationally processing at NASDA/EOC. This paper describes the in-water algorithms Version 1.0 for chlorophylla concentration, pigment concentration, and attenuation coefficient at a wavelength of 490 nm. The selected OCTS standard algorithms (Ver. 1.0) are as follows:

Active erosion of Undaria pinnatifida Suringar (Laminariales, Phaeophyceae) mass-cultured in Otsuchi Bay in northeastern Japan

Chl = 0.2818 \left( {\frac{{L4 + L5}}{{L3}}} \right)^{3.497 }