An attempt was made to measure diameter, pervalvar axis (height), long height, short height and height of half spheroid in order to propose the simple method for estimating biovolume of diatoms, the genus Coscinodiscus. Pervalvar axis (height), long height, short height and height of half spheroid increased linearly with increasing diameter, and species-specific regression equations of the diameter-height relationships were obtained for elliptically cylindrical C. curvatulus, C. nitidus, C. radiatus, C. wailesii and all these four species and of the diameter-long height, diameter-short height and diameter-height of half spheroid relationships were obtained for an asymmetrically cylindrical with add two half spheroids C. granii. For all of these cases, there are not statistically differences between biovolume estimated by the former Hillebrand’s equations and one estimated only from diameter using the simple equations obtained in the present study.

In recent years, Chattonella has frequently caused red tides in the inner part of the Ariake Sea. However, information on the cyst in the sea is currently limited. In the present study, cyst germination of Chattonella was investigated from 2011 to 2013 at 10 stations. Development of vegetative cells of Chattonella was also monitored at 6 stations. The numbers of germinated cysts ranged between 1.38±1.38 and 3.71±2.33 cysts cm^-2. The number was low in 2012 when no Chattonella bloom had occurred the previous summer. Although cyst germination was low at station S3, vegetative cells of Chattonella were detected first at that station in 2012 and 2013. At S3, the number of vegetative cells was also high as compared to the 6 stations investigated; hence, population development of Chattonella vegetative cells may not necessarily occur at the station where the cysts germinated. Moreover, in addition to maturation, cyst survival is considered an important process for germination the following spring.

A large number of linguliformean brachiopod larvae were collected from off the coast of Kagawa Prefecture in the easten portion of the Seto Inland Sea, Japan. Larvae of various sizes with embryonic shells were identified as Lingula spp. with the number of cirri increasing with age up to 11 pairs. Those larvae without embryonic shells were identified as Discradisca spp. which are characterized by three stages: (1) having remarkably long embryonic setae but lacking larval shells, with up to four pairs of cirri, (2) formation of larval shells and retaining the long embryonic setae and (3) larval shells with curved setae and losing the embryonic setae. Planktonic larvae of these brachiopods are easily collected by plankton net and readily segregated into each family by means of the presence or absence of embryonic shells. Therefore, the plankton collecting is a useful method for the preliminary survey of lingulid brachiopods.

Recently, frequent blooms of the commercially harvested rhizostome jellyfish Rhopilema esculentum have occurred in the Ariake Sea, western Japan. We attempted to estimate the abundance and biomass of the jellyfish in the inner and middle parts of the sea in the warm seasons of 2012. The maximum abundances of individuals occurring in the surface waters of these areas were around 408–525 （inner part, August and September） and 365（middle part, October） indiv. per km², respectively. The jellyfish seemed to be distributed in patches. Based on the abundances in the inner and middle parts of the sea, the biomasses were estimated as approximately 3,264–4,200 t and 7,300 t in wet weight, respectively.

FlowCAM^® is an imaging flow cytometer originally designed to characterize particles ranging from 20–200 µm. It provides an image-collage of captured particles and various numerical morpho-characters of each particle. This unique instrument is now widely used in planktology, especially in phytoplankton studies, aiming to reduce microscopy efforts and obtain detailed morphological data on planktonic particles. Because it can provide a continuous record of plankton occurrence and allows detection of rare plankton in its trigger modes, the application of FlowCAM in field research is of interest, especially for red-tide surveys. During our trials for wide-range surveys over the entirety of Tachibana Bay and the Ariake Sea (Nagasaki, Japan), FlowCAM was set onboard the research vessel Yumetobi (19 GT) and continuously monitored the occurrence of notorious red-tide causative raphidophytes Chattonella spp. along a total 148 km cruise line. FlowCAM detected dense occurrences of Chattonella antiqua at the mouth of Tachibana Bay, which continuously appeared to flow into the Ariake Sea. Even during a single cruise, numerous data on Chattonella occurrences were obtained–enough to analyze the water mass transporting the population from the Ariake Sea to Tachibana Bay. In the inner part of Tachibana Bay, on the contrary, no cells were detected over the 13 km cruise line, suggesting the area was tentatively free from red-tide risk; such judgment was not possible with regular on-station samplings. Prior to applying FlowCAM for such surveys, researchers must be careful to select the objective lens (×4 or ×10) and carefully calibrate the system for each target species, because the magnification that is chosen affects processing fluid volume and focal depth, which further affects the minimum detection limit and quantitativity.

The harmful dinoflagellate Karenia mikimotoi is responsible for extensive red tides in the western part of the Seto Inland Sea and causes severe fish-kills. There is great demand by fishermen for a red tide monitoring system covering wide areas, however, manual sampling and microscopy-based detection used in the current monitoring system is time intensive, and makes wide-area surveys almost impossible. In this study, we applied FlowCAM to enumerate K. mikimotoi occurrences in the field and compared the results with conventional microscope counting. The field surveys were carried out in Suo-Nada, Iyo-Nada, and Beppu Bay in June and July from 2010 to 2012. No significant difference was found in the quantification results obtained by both methods at rather low density occurrences of K. mikimotoi (<10 cells mL^-1). However FlowCAM was more advantageous in enumerating mid-density occurrences (<100 cells mL^-1) which are critical for monitoring the status of forthcoming red tides. Furthermore, images captured by FlowCAM allowed identification of what seems to be a characteristic phenomenon in which diatoms are usually scarce prior to red tides of K. mikimotoi.

Monitoring technology for Lake Biwa using imaging methods has been developed since the 1980’s. The autonomous underwater robot “Tantan”, designed for monitoring the lake environment with a high resolution digital camera, was first built in 2000, and applied for monitoring of the lake floor from 2002 to 2010. Recently, dissolved oxygen (DO) depletion has become a serious problem in the deep areas of Lake Biwa because of eutrophication and global warming, and has led to critical issues in the conservation of endemic species. In this study, the population and the rate of pre-copulation of Jesogammarus annandalei (Crustacea, Amphipoda, Anisogammaridae) were investigated using the underwater vehicle to assess the effect of low oxygen. The minimum population of J. annandalei was 1.7 inds. m^-2 in December 2004 when DO at 90 m depth was 1.6 mg L^-1, and the maximum population was 1322 inds. m^-2 in December 2003 when DO was 6.1 mg L^-1. The rate of pre-copulation varied between 0.4% in December 2002 and 50.5% in December 2005. High pre-copulation rates were observed when the water temperature was around 7.7–7.8°C and DO was around 2.4–2.5 mg L^-1. These results suggest that small windows of water temperature and DO might have a profound effect on the pre-copulating behavior. Such monitoring methods, utilizing an underwater robot like “Tantan” provide many advantages such as knowing the behavior of the benthos as well as observing and monitoring the wider lake floor.

Holography is an optical technique that can record three dimensional information of a sampling space in its entirety with information on the structure of objects and their location within the space. The first use of an underwater holographic camera for observations of planktonic organisms was in 1970. Underwater digital Holographic cameras, such as LISST-HOLO (Sequoia Scientific, Inc.) are now commercially available. The resolution and characteristics of reconstructed images of planktonic organisms and artificial aggregates obtained by LISST-HOLO were examined in the present study. Resolution of reconstructed images depended on the area of the hologram for their calculation. Reconstructed images showed sharp outlines of objects but thin slices could not display the inner structure of them. The underwater digital Holographic camera, LISST-HOLO, could be a powerful tool for observations on the distribution of micro- and meso-plankton when they are more abundant than 10–100 individuals L^－1.

The Fisheries Research Agency of Japan has been conducting spawning surveys of pelagic fish in the Kuroshio area since 1947 and a huge amount of formalin-preserved zooplankton samples from an extensive area has been stocked. While the total biomass (wet-weight) of every sample has been analyzed, the taxonomic composition has been analyzed only for limited samples, because it requires taxonomic skill, much effort and time. Since the size composition of zooplankton is very important information for analyses on the quality of food for larval fish, we designed the bench-top Video Plankton Recorder (B-VPR) to analyze the abundances and size compositions of copepods in formalin-preserved samples more rapidly and conveniently. Using B-VPR, one plankton net sample (ca. 10000 particles) can be imaged and analyzed within 90 min. We have already analyzed over 4000 samples of zooplankton collected in the Kuroshio area since the 1960s. From the results of the B-VPR analyses, long-term variations in the size composition of copepods was observed. Long-term monitoring is necessary to analyze the mechanisms attacting the dynamics of fish stocks. B-VPR will be a useful instrument for analyses of large numbers of samples for long-term monitoring.

The Video Plankton Recorder (VPR) is a non-invasive optical sampling system that enables in situ observations of associations between zooplankton and fragile marine snow aggregates. Here we employed the VPR to observe attachment and feeding behavior of oncaeid copepods to marine snow in the field. VPR surveys were conducted in the surface waters (0–100 m) of the Kuroshio region off Shikoku during February 2011. We recorded images of oncaeid copepods being attached to discarded and occupied appendicularian houses, and amorphous aggregates in the area. These observations suggest that oncaeid copepods utilize these particles as food sources, since they are primarily substrate feeders. In particular, more than 80％of attached individuals were found on discarded appendicularian houses, indicating a close trophic coupling between the oncaeids and the houses. The implications for aggregate colonization behavior of oncaeid copepods are also discussed on the basis of the VPR observations.

An individual zooplankter behaves in response to its environment. If we look closely into the vertical distribution of zooplankton, we can find a species-specific pattern of vertical distribution. In other words, plankton specifically have favorite conditions within their environment. This preference may differ between species and even between developmental stages of a single species. So far, population dynamics of zooplankton have been investigated in both neritic and oceanic waters. The dynamics is attributable to the sum of the fate and behavior of each plankter; therefore, measurement of the vertical and horizontal distributions of zooplankton together with environmental properties should be more fruitful than spatially-averaged measurements. Modern technologies to measure the fine scale vertical distributions of zooplankton are introduced to monitor the spatial distributions and temporal fluctuations of zooplankton. We here target small-sized copepods, which play a pivotal role in aquatic ecosystems, considering their ubiquity in both neritic and oceanic waters. Here we propose two methods to achieve fine scale measurements of zooplankton: a new apparatus that employs bellows to sample plankton; and a digital holographic imaging device. Our devices can detect a range of sizes of targeted planktonic organisms of 300 µm to 1 mm. The detection limit of zooplankton population density is set as low as 1 ind. L^-1 The maximum spatial resolution is less than 1 m in our devices.

An Autonomous Visual Plankton Recorder (AVPR) was used to record colour in situ images of plankton and other marine particulates at several oligotrophic stations around the world, including a northern hemisphere subtropical open ocean, a northern hemisphere subtropical marginal sea, a southern hemisphere tropical marginal sea, and a polar open ocean. Quantitative analyses and comparisons of particle concentrations, sizes and vertical profiles were possible after identification of optimal image enhancement settings and employment of a specially-developed macro routine in the off-the-shelf image analysis software Image Pro Plus. Such baseline data is invaluable for assessing the effects of surface or near-surface waste water or tailings disposal during deep-sea mining operations in oligotrophic areas. Marine particulate profiles, their relationships to oceanographic parameters and water mass structure, and the resolution-dependent limitations of the system are introduced and discussed.

Although problematic jellyfish blooms have frequently been reported in recent decades in many parts of the world ocean, studies of long-term monitoring based on accurate measurements of abundance and biomass of jellyfish populations are few. Pronounced patchy distributions shown by medusae, such as Aurelia aurita s.l., have precluded researchers from accurate determinations, and some visual and acoustic instruments have been used to replace the traditional sampling gear, i.e. plankton net or trawl. We introduce use of a Dual frequency IDentification SONar (DIDSON, Sound Metrics Co.), a high-definition imaging sonar that provides near-video-quality images of underwater objects, to jellyfish ecological studies. We deployed the DIDSON in a shallow, enclosed water mass where A. aurita medusae dominated, and determined their spatiotemporal distributions, numerical abundances and biomass much more accurately than with conventional net sampling. Therefore, we conclude that the DIDSON can be a powerful tool to monitor the population density and spatial distribution of relatively large jellyfish (bell diameter: >ca. 5 cm) in shallow (<10 m) coastal waters, where problematic jellyfish often bloom.

An imaging system using a digital single-lens reflex camera with a macro lens and LED illuminator mounted on a glass folding table was examined for accumulating metadata on zooplankton samples. As a result of resolution tests of the imaging system using a stage micrometer (each division＝10 µm), resolutions at each magnification value, 0.15×, 0.37×, 1.3× and 2.6× were estimated as 89, 35, 10 and 5 µm approximately. The dark field images of zooplankton samples were high resolution/high color rendering enough to obtain metadata. The bright field images could be utilized for observations of pigments and oil sacs of copepods. We concluded that the imaging system is economical, easy to operate and is a useful system for zooplankton monitoring and metadata accumulation.

Computer-automated image capture and analysis techniques are increasingly used for the study of plankton. Unfortunately, because most of the automatic image processing software packages recognize only numbers of pixels and grey scale values, although a great many parameters are automatically measured on each image (area, perimeter, average level of grey, etc. . . .), these do not directly equate to variables that appear in the biological literature. The relationships between prosome lengths and computer-generated characters were derived from images acquired using the ZooScan system for two of the most common copepod families off south–eastern Japan: Calanoida and Poecilostomatoida. The equivalent spherical diameter (ESD), a character automatically measured by the ZooScan-ZooProcess system, was found to be highly correlated with prosome length in the two orders, and a single equation could be established (regression coefficient r² = 0.943) for all Calanoida excepting those of the family Eucalanidae: PL (mm)＝0.08＋0.023*ESD (pixels).

The Okazaki Large Spectrograph (OLS), built in 1980 at the National Institute for Basic Biology（Okazaki, Japan）as a cooperative research facility, has been used for active spectroscopical studies by visiting scientists inside and outside countries. The OLS can project a wavelength spectrum from 250 nm (UV) to 1,000 nm (IR) onto horseshoe-shaped focal curve (10 m long), and irradiate different samples simultaneously. On the focal curve, the photon flux density of monochromatic light is 80 µmol m^-2 s^-1 at 300 nm and 160 µmol m^-2 s^-1 at 600 and at 900 nm, which is more than twice as much as that of the corresponding monochromatic component of tropical sunlight at noon. Recently, studies on photo-germination of resting stage cells in diatoms and phase-shift of diel vertical migration rhythm in red-tide flagellates have been conducted using the OLS. We believe that our facility can be used to clarify mechanisms of various photobiological responses in plankton.