Takashi Yoshikawa

Tokai University

Although marine cladocerans are known as coastal zooplankton, they sometimes appear in offshore waters in large numbers. In Suruga Bay, located in the center of Japan and opens to the Pacific Ocean, cladocerans occur abundantly in offshore waters during the spring and summer seasons. However, the mechanisms by which these offshore populations form...

Seasonal occurrences of marine cladocerans in offshore Suruga Bay, Japan, were studied from 2014 to 2019. Zooplankton samples were collected monthly from a station (depth: ca. 1000 m) located in the offshore area of the bay. Cladocerans appeared each year from February to December, and disappeared in January. Their abundance in- creased drastically...

Seasonal and vertical variations in photosynthetic–irradiance (P–E) parameters and primary production were examined in offshore Suruga Bay, where both the subtropical warm Kuroshio Water and eutrophic coastal water were influential. The maximum light-utilization coefficient, α*, did not show significant variation between the surface and subsurface...

To evaluate the seasonal water circulation of Tonle Sap Lake and its tributary rivers in Cambodia, the spatial distribution patterns of major and trace elements in surface water were investigated. Based on the similarity of the dissolved elemental concentrations, the water samples were mainly divided into the three groups: samples with relatively h...

Phytoplankton primary production and its regulation by light and nutrient availability were investigated in the shallow, tropical coastal waters of Bandon Bay, Southern Thailand. The bay was meso-eutrophicated and highly turbid, receiving river water discharge. Water column stratification was consistently weak during both rainy and dry seasons. Dis...

Erratum to: Fish Sci (2017) 83:635–647 DOI 10.1007/s12562-017-1098-9.

The possible impacts of resuspension of low-density bottom sediments on the microbial decomposition process of organic matter were investigated at a coastal fish farming area. Hydrolysis and mineralization rates were much higher in sinking particles, resuspendable particles, and bottom sediments than in seawater. The cell-specific mineralization ra...

The stock unit used in fisheries resource assessment and management is generally based on the morphological and genetic characteristics of a particular population or species to avert problems caused by the treatment of multiple populations as one stock, which can lead to the overestimation of population sizes and genetic pollution. Furthermore, sin...

Estimation of the origin of coastal sediment is an important work for preservation of a tidal land. In this study, the total of 16 sediment samples were collected from the Mikawa bay and two rivers, including Yahagi River and Toyo River and the concentration of rare earth elements (REEs) and strontium isotope were measured with ICP-MS technology an...

We assessed the role of planktonic processes, in comparison to allochthonous input from fish cages and sedimentary loss, in the organic carbon (OC) budget of the water column in a semi-enclosed fish-culturing area (culturing red sea bream Pagrus major and yellow tail Seriola quinqueradiata). The sedimentation rate of particulate organic carbon (POC...

Microbial mineralization rates in sinking particles, bottom sediments and seawater were determined in a coastal fish (red sea bream Pagrus major) culturing area to clarify the mineralization process of organic matter (OM) in the entire water column. The mineralization rates of 14C-labelled glutamate and glucose per unit volume were highest in the s...

A very small strain of the freshwater rotifer Brachionus angularis (Laos strain) was isolated in Vientiane, Laos. We investigated the morphology as well as grazing and growth characteristics of this strain. The lorica of the Laos strain was round, 86.0±4.9μm (mean±SD) in length, with a few small spines. These morphological characteristics make the...

Regional variations in the contribution of non-photosynthetic pigments (ā np*) to the total light absorption of phytoplankton (ā ph*) and its influence on the maximum quantum yield of photosynthesis (φ m) were investigated. In the western equatorial Pacific, the surface ā np* : ā ph* ratio was higher in the western warm pool than that in the upwell...

Vertical variations in the photosynthesis–irradiance (P–E) parameters and their effects on the primary production (PP) were examined in four different characteristic coastal and offshore areas in Japan Sea and the East China Sea, during a stratified season. In Japan Sea, no significant regional variations were observed in the P–E parameters at a de...

To estimate the clearance rates of pico- and nanophytoplankton by heterotrophic nanoflagellates (HNF) and ciliates, the size-fractionation method was employed in combination with a multiple regression analysis. Apparent growth rate of a specific phytoplankton group was decomposed into three terms, net growth rate, grazing rates by HNF and those by...

The latitudinal variation in the photosynthesis-irradiance (P-E) relationship of phytoplankton was investigated across a cyclonic eddy in the Antarctic Divergence zone along the 140°E longitude. Both the maximum photosynthetic rate (P*max) and maximum light utilization coefficient (alpha*) were lower at stations within the eddy as compared with tho...

The influence of phytoplankton photosynthesis (PP) on dissolved oxygen (DO) dynamics was evaluated in a red sea bream (Pagrus major) aquaculture site. The surface PP was monitored continuously by a natural fluorescence sensor for 2–3 weeks during all seasons, except spring. In summer, when the daily PP was low during cloudy weather, DO at the surfa...

Effects of diurnal variation in phytoplankton photosynthesis on estimating daily primary production (DPP) were examined using field data from Sagami Bay, Japan. DPP at 5m depth was calculated from the continuous data of chlorophyll a (Chl a) and light intensity monitored by a natural fluorescence sensor with and without considering time-dependent c...

In order to apply the natural fluorescence method for the long-term monitoring of chl a and primary production, the seasonal variation in the light absorption coefficient of phytoplankton (a(ph)*), maximum quantum yield ratio of photosynthesis to fluorescence [(phi(c)/phi(f))(max)], and its light saturation index (k(cf)) were examined. The mooring...

In vivo chlorophyll fluorescence of phytoplankton has been keenly used as an indicator of the photosynthetic competence since 1960s. Recently, several attempts on the estimation of phytoplankton photosynthetic rate (i.e. primary productivity) in natural waters have been made using passive and active fluorescence techniques. Here we briefly introduc...

In order to evaluate the carrying capacity of Otsuchi Bay, Iwate Prefecture, Japan, natural fluorescence method was examined for continuous monitoring of chlorophyll a and primary production. Light-absorption coefficient of phytoplankton (a(ph)) and the quantum yield ratio of photosynthesis to fluorescence (phi(c)/phi(f)) needed for estimation of p...

Production and erosion of the commercially mass-cultured kelp Undaria pinnatifida Suringar f. distans Miyabe et Okamura were investigated between January and April 1998 in Otsuchi Bay, ca. 8 km long and 2 km wide, located on the northeastern coast of Japan. Steady growth in total kelp length was observed from January to March, with rates of 1.1 to...

Temporal variations in transparent exopolymer particles (TEP) were studied during a spring bloom (January to April 1998) in a subarctic ria on the northeast coast of Japan. A diatom-dominated bloom developed from mid-February. Two major peaks were recorded in the first and last week of March, during which chlorophyll concentrations reached the maxi...

The light-saturated maximum value (P Bmax) and initial slope (α) of the photosynthesis-irradiance (P-E) curve were examined in a warm streamer, a cold streamer and a warm core ring off the Sanriku area in the subarctic western North Pacific Ocean during an ADEOS/OCTS Sanriku field campaign in early May 1997. BothP Bmax and α were within the ranges...

研究概要:Geographical variability in the relationship between photosynthesis and irradiance in summer phytoplankton populations was examined in the subarctic North Pacific Ocean in July-August 1997 and July 1999. Photosynthesis versus irradiance (P-E) curves were obtained for seawater that were collected by trace metal clean techniques. Most region sam...