The effects of chemicals in sediments in coastal areas on environmental organisms are almost unknown, although a number of investigations on the distribution of pollutants in these sediments were performed, often resulting in the detection of chemical residues with high concentrations. In this study, toxicities of sediments collected from 11 locations in Hiroshima Bay, Japan, was assessed using embryos of Java medaka, Oryzias javanicus. The embryos were placed on sediments containing a little pore water without adding overlying water. The results showed that as high as 37% of the embryos exposed to sediments collected near Hatsukaichi City died. Additionally, the mortality was 33% at a site distant slightly from an industrial area in Otake City. Delayed hatching was observed at six locations. Thus, the certain effects of exposure to sediments collected from the bay in the embryos were observed, and the authors concluded that these effects are most likely to have been caused by chemicals in the sediments.
Anthropogenic substances reach sea areas, absorb particles and finally pile up on sediments. Although previous studies investigated the distribution of pollutants and detected a high concentration of pollutant residues in Japanese coastal areas, the effects of these residues on benthic organisms have been almost unknown. In fact, methods to assess sediment toxicity have not been established, and it is not easy to assess the toxicity of sediments collected from the sea bottom. In this study, we worked to assess the maximum impact of toxic sediments on benthic organisms by exposing marine medaka to extracts from sediments collected from five sites in Tokyo Bay, Japan. The results showed that sediments collected at two sites caused fatal effects on marine medaka. Furthermore, marine medaka were also exposed to three fractionation processes of varying polarity extracts. The results of these exposure tests indicated the possibility that such sediment extracts may have caused antagonistic effects.
Metabolomics allows for comprehensive assessment of the current state of organisms by collecting information on variations on low₋molecular₋metabolites, which can take different forms to maintain homeostasis even under the influence of chemical exposures or external stressors. Metabolomics workflows include chemical analysis designed to obtain the assessment of metabolites, statistical analysis, research on the metabolic state of organisms and the prediction of their health trajectories. Until now, we have examined and assessed the effects of pollutants on Japanese medaka through the metabolomics approach. In this publication, we describe the metabolomics approach with GC/MS analysis, which includes fish treatment procedures, and its assessment process.
Organo-tin compounds, which used to act as anti-fouling agents, have still been detected in the marine environment almost 30 years after their use was prohibited in Japan. The 2011 Great East Japan Earthquake triggered a giant tsunami and caused bottom sediments along the deeply indented Pacific coastline to be stirred up on a large scale. Nevertheless, researchers have not investigated in detail how these sediments have been stirred up and how this phenomenon has affected the marine environment. This study aims to elucidate the horizontal and vertical distribution of residual organo-tin compounds in bottom sediments in Otsuchi Bay, a main semi-closed bay on the Sanriku coast. For this purpose, bottom-sediment core sampling was conducted at multiple stations in this bay. As a result, it is revealed that the original component of Organo-Tin compounds has still been remaining and that their concentration is significantly higher near a shipyard located in the inner part of the bay.
Marine-fouling organisms, such as barnacles and mussels, cause serious problems by settling on ship hulls and submerged artificial structures in addition to natural habitats. To develop novel antifouling technologies, including new antifouling paints, bioassays are indispensable for assessing the efficacy of these technologies and their environmental impacts. Since biofouling is a complicated biological event, it is difficult to conduct biofouling assays without using fouling organisms. Although detailed genetic information on most of the fouling organisms is unknown and methods to use these organisms for lab-experiments have not been well established, the intertidal barnacle Amphibalanus amphitrite is thought to be a model creature for larval settlement assays to investigate settlement mechanisms and antifouling technologies. This review describes bioassays using sessile organisms such as A. amphitrite conducted for my studies on barnacle larval settlement and the development of antifouling paints.
Only a few studies have been devoted to the species identification and the distribution of marine hydroids Ectopleura in Japanese coastal waters, despite the scale of fouling problems that they pose. We collected polyps from the coast of the western and northern parts of Japan, and analyzed their morphological characters and mitochondrial COI genes. As a result, while polyps settled on fishing nets along the coast of Hokkaido were Ectopleura radiata, E. crocea were spotted along the Pacific coast of Honshu. Dense polyp colonies on pontoons along the coasts of Seto Inland Sea in mid-to-late winter were also identified for the first time as E. radiata. In addition, phylogenetic analysis has identified Ectopleura sp. JRH-2014 spotted in the China Seas as E. radiata. Regarding actinulae of E. radiata, we devised a new assay composed of hexagonal columnar cell using test slide glasses, and a magnetic stirrer, and examined the settlement inhibitory effects of the silicone-based coatings. The results found that actinulae proved very sensitive to copper pyrithione contained in anti-fouling agents and the age of coatings.
In our previous study, we made a portable apparatus simulating a seawater cooling intake water pipe and confirmed its effectiveness assessing the antifouling effects of chemical agents on sessile organisms. In this study, we used the apparatus to see if the use of different chlorine sources (sodium hypochlorite solution and seawater electrolyte) could lead to a gap in these antifouling effects. The authors conducted a 25-day seawater flow-through experiment using seawater electrolyte as a chlorine source between 28 November and 22 December 2014. The nominal total residual chlorine concentration levels were 0 (control), 0.04, 0.08, and 0.16 mg/L as a factor. At the end of the experiment, the total number and weight of sessile organisms at the result of the experiment were compared with the result of the previous experiment that used sodium hypochlorite solution as a chlorine source. When comparing the results of the two, we learned that the residual chlorine concentration levels, which affect the number and weight of attached barnacles, hydrozoa, and biofilms, were not significantly different despite a difference in chlorine sources, and that the antifouling effects of both chlorine sources are considered to be almost same.
Bioassays are a useful tool for assessing the effect of effluents on organisms. However, there are only a few bioassays established using marine organisms. Moreover, conventional bioassay procedures require enormous amounts of time and labor. In this study, the authors have developed a rapid and simple bioassay using seaweed Pyropia yezoensis (conchospores and juvenile sporophytes), and bioassay tests were performed upon a 96 well microplate. The growth rate of an endpoint was determined by fluorescence intensity of chlorophyll using a plate reader. Through daily monitoring, this method could calculate the most minimum EC50 for major heavy metals and toxic compounds. A trial with sporophytes could detect the effect of harmful substances more sensitively than a test using conchospores. In addition, the sporophytes test showed detection sensitivity to toxicants similar to that of a test with microalga Skeletonema marinoi-dohrnii. The sensitivities of conchospores and sporophytes tests to heavy metals were equal to those with various other seaweeds. We propose a rapid and simple seaweed bioassay using a microplate and a fluorescence plate reader.
Recently, IMO has been strengthening its regulations on CO2 emission from marine vessels. One of the effective solutions to comply with these regulations targeting marine engines is to increase the thermal efficiency with higher compression ratios. However, the optimum compression ratio depends on engine output power. Given this, we have developed a variable compression ratio (VCR) system for two stroke crosshead engines for marine applications that can change compression ratios seamlessly during engine operations.
The newly developed VCR system demonstrated that it can change compression ratios at its will while the engine is running. In addition, the authors found that the VCR system can also decrease fuel consumption and CO2 emissions with a higher compression ratio. In consideration of these points, the VCR system was awarded the 2018 Marine Engineering of the Year (Dokou’s Memorial Award).