Does heavy oil pollution induce bacterial diseases in Japanese flounder Paralichthys olivaceus?

As basic research for the effect of heavy oil on the fish immune system, in this study, the number of leukocyte was counted in Japanese flounder Paralichthys olivaceus, after exposure to heavy oil at a concentration of 30 g/8L for 3 days. To compare the numbers of bacteria in the skin mucus between oil-exposed and control fish, viable bacteria were enumerated by counting colony forming unit (CFU). Compared with 5.79+/-1.88 x 10(7)leukocytes/mL in the controls, the exposed fish demonstrated higher counts, averaging 1.45+/-0.45 x 10(8)cells/mL. The bacterial numbers of control fish were 4.27+/-3.68 x 10(4)CFU/g, whereas they were 4.58+/-1.63 x 10(5)CFU/g in the exposed fish. The results suggest that immune suppression of the fish occurred due to heavy oil stressor, and bacteria could invade in the mucus, resulting in the increasing leukocyte number to prevent infectious disease.     

Diel vertical migration of the copepod Calanus sinicus before and during formation of the Yellow Sea Cold Bottom Water in the Yellow Sea

To understand the effects of the Yellow Sea Cold Bottom Water(YSCBW)on the diel vertical migration(DVM)of the copepod Calanus sinicus,we surveyed vertical distribution of C.sinicus at a fixed station in the Yellow Sea before(spring)and during(summer)formation of the YSCBW.Cold water(<10 C)was observed in the bottom layer when the water column was thermally stratified in summer,but the water column was thermally well-mixed in spring 2010.Samples were collected from five different layers at 3-h intervals using an opening-closing net.Adult females(1–155 ind./m3)showed a clear normal DVM pattern throughout the entire water column in spring,whereas adult males did not migrate.DVM of copepodite V(CV)individuals was not clear,but the maximum abundance of CI–CIV occurred consistently in the upper 10–20 m layer,where there was a high concentration of chlorophyll-a(Chl-a)(0.49–1.19μg/L).In summer,weak DVM was limited to cold waters beneath the thermocline for adult females(<30 ind./m3),but not for adult males.The maximum abundance of CI–CIV also occurred consistently in the subsurface layer(20–40 m)together with high concentrations of Chl-a(0.81–2.36μg/L).CV individuals(1–272 ind./m3)moved slightly upward nocturnally to the near-surface layer(10–20 m),where the average temperature was 25.74 C,but they were not found in the surface layer(0–10 m;28.31 C).These results indicate that the existence of the YSBCW affected food availability at depth and the vertical temperature distribution,leading to variation in the amplitude and shape of stage-specific vertical distributions(CI to adults)in C.sinicus before and during the formation of cold waters in the Yellow Sea during the study period.     

High-frequency acoustic backscattering characteristics for acoustic detection of the red tide species Akashiwo sanguinea and Alexandrium affine

Harmful algal blooms(HABs),caused by the overgrowth of certain phytoplankton species,have negative effects on marine environments and coastal fisheries.In addition to cell-counting methods using phytoplankton nets,a hydroacoustic technique based on acoustic backscattering has been proposed for the detection of phytoplankton blooms.However,little is known of the acoustic properties of HAB species.In this study,as essential data to support this technique,we measured the acoustic properties of two HAB species,Akashiwo sanguinea and Alexandrium affine,which occur in the South Sea off the coast of Korea.Due to the small size of the target,we used ultrasound for the measurements.Experiments were conducted under laboratory and field conditions.In the laboratory experiment,the acoustic signal received from each species was directly proportional to the cell abundance.We derived a relationship between the cell abundance and acoustic signal received for each species.The measured signals were compared to predictions of a fluid sphere scattering model.When A.sanguinea blooms appeared at an abundance greater than 3 500 cells/mL,the acoustic signals varied with cell abundance,showing a good correlation.These results confirm that acoustic measurements can be used to detect HAB species.     

Influences of diel and tidal cycles on fish assemblage in eelgrass (Zostera marina) bed of southern Korea during autumn

Short-term tidal and diel variations of autumn fish assemblage in a Zostera marina bed were investigated using 3 h interval samplings for 24 h in both spring and neap tide using a small beam trawl. A total of 1 346 fishes belonging to 19 species were collected at spring tide, whereas 1 115 fishes belonging to 17 species were at neap tide. The common fish species were Nuchequula nuchalis, Acanthogobius flavimanus, Takifugu niphobles, Acentrogobius pflaumii, and Pholis nebulosa with the former three species dominating at spring tide, while the latter two species being abundant at neap tide. Diel variation in abundance was significant with higher abundance at night than day, but there were no significant differences between spring and neap tides, and between ebb and flood tides (three-way ANOVAs). Diel variation in the abundance of fishes may be influenced by tidal range and cycle, and day-night differences of food availability and behaviors of fishes indirectly. Non-metric multidimensional scaling (nMDS) ordination and analysis of similarity (ANOSIM) results revealed significant differences in species compositions both between day and night, and between spring and neap tide. Eelgrass beds are highly productive marine ecosystem, and thus, our results will contribute to conservation of seagrass ecosystem in the study area.     

First Investigation of Microbial Community Composition in the Bridge (Gadeok Channel) between the Jinhae-Masan Bay and the South Sea of Korea

Microbial community composition varies based on seasonal dynamics (summer: strongly stratified water column; autumn: weakly stratified water column; winter: vertically homogeneous water column) and vertical distributions (surface, middle, and bottom depths) in the Gadeok Channel, which is the primary passage to exchange waters and materials between the Jinhae-Masan Bay and the South Sea waters. The microbial community composition was analyzed from June to December 2016 using 16S rRNA gene sequencing. The community was dominated by the phyla Proteobacteria (45%), Bacteroidetes (18%), Cyanobacteria (15%), Verrucomicrobia (6%), and Actinobacteria (6%). Alphaproteobacteria (29%) was the most abundant microbial class, followed by Flavobacteria (15%) and Gammaproteobacteria (15%) in all samples. The composition of the microbial communities was found to vary vertically and seasonally. The orders Flavobacteriales and Stramenopiles showed opposing seasonal patterns; Flavobacteriales was more abundant in August and December while Stramenopiles showed high abundance in June and October at all depths. The genus Synechococcus reached extremely high abundance (14%) in the June surface water column, but was much less abundant in December water columns. Clustering analysis showed that there was a difference in the microbial community composition pattern between the strongly stratified season and well-mixed season. These results indicate that the seasonal dynamics of physicochemical and hydrologic conditions throughout the water column are important parameters in shaping the microbial community composition in the Gadeok Channel.     

Digital Photogrammetry and Microscope Photographs

The feasibility of applying commercial digital photogrammetric software to the measurement of small objects photographed through an optical microscope has been examined. The objects, about 20 mm across, were photographed using a 35 mm film camera (at the lowest magnification setting of the Olympus microscope) giving photographs at a scale of 2:1. The photographs were then scanned before processing with the VirtuoZo digital photogrammetric system. Various problems needed to be overcome, some due to the limited options available with the highly automated digital system which was not designed for such measurement tasks. The unusual image scales, the uncommon pixel sizes and the unconventional and uncertain imaging geometry, all impeded immediate photogrammetric implementation. Photographic problems with the microscope were also faced, as with all microscope photogrammetry. Creating control points and independently assessing the accuracy of results at these scales were also difficult operations, but an analytical plotter was utilized for both these purposes and to verify the imaging geometry. Once such problems were overcome, image matching proceeded well and an accurate DTM could be created successfully, provided that a suitably textured object was chosen.     

Linear wave reflection by trench with various shapes

Two types of analytical solutions for waves propagating over an asymmetric trench are derived. One is a long-wave solution and the other is a mild-slope solution, which is applicable to deeper water. The water depth inside the trench varies in proportion to a power of the distance from the center of the trench (which is the deepest water depth point and the origin of x-coordinate in this study). The mild-slope equation is transformed into a second-order ordinary differential equation with variable coefficients based on the longwave assumption [Hunt's, 1979. Direct solution of wave dispersion equation. Journal of Waterway, Port, Coast. and Ocean Engineering 105, 457–459] as approximate solution for wave dispersion. The analytical solutions are then obtained by using the power series technique. The analytical solutions are compared with the numerical solution of the hyperbolic mild-slope equations. After obtaining the analytical solutions under various conditions, the results are analyzed.     

Description of feeding apparatus and mechanism innemopilema nomurai kishinouye (scyphozoa: rhizostomeae)

Feeding apparatus, mechanism and passage of ingested prey were described forNemopilema nomurai (Scyphozoa: Rhizostomeae).N. nomurai medusae without central mouths have developed complicated canal systems connecting the tip of the tentacle and oral arm to the gut cavity. The number of junctions in the canal system increases with the bell diameter. The prey is gathered by paralyzing nematocyst at the tentacles and by adhering cirri at the oral arms and scapulets. They are engulfed into the terminal pore located at the oral arms and scapulets, and entered into the gut cavity via the canal system. The estimated digestion time is 1 hour and 20 min. The diameter of terminal pore is always about 1 mm, implying that they could not eat prey larger than that pore size. On the other hand, ephyrae have central mouths and could swallow prey as large as adults could. Exploitation of the same size of food by adult and ephyra implies thatN. nomurai can affect seriously the whole food web, massively ingesting micro-and mesozoopl a n k t o n and cutting the energy transfer toward the higher level of carnivores.