The present research seeks an appropriate method of monitoring both submerged and exposed seagrasses. A seagrass mapping technique was developed using combination data sets from satellite images, digital maps, SONAR imagery and handheld-GPS data collected from seagrass meadows (Zostera marina) at Shinkawa–Kasugagawa estuary, the Seto Inland Sea, Japan, in September 2011. The entire coverage area of 123,000 m2 was calculated from 638 captured SONAR images. Zostera meadows were observed at water depths of 1.6–5.0 m, over sandy sediments. Zostera was not found at water depths greater than 5.0 m, where the sediments are muddy. The canopy height of Z. marina was estimated to vary between 14 and 87 cm. Additional mapping of intertidal seagrass meadows of Halodule pinifolia was also carried out in Rayong Province, Thailand, by GPS tracking during April 2009 and December 2010. Coverage areas varied between 33,498 and 76,207 m2, and the highest coverage area was found in April 2009. The present study demonstrates that the entire area of both submerged and exposed seagrass meadows can be calculated by simple methods in a short time with acceptable accuracy.
The effect of 70% ethanol preservation (for three days) on bulk stable isotope measurements of carbon and nitrogen in marine predators (squid and fish) were examined. A total of 17 different species collected from a wide range of latitudes (15°S–65°N) in the Pacific Ocean were used in the analysis. In agreement with previous studies, ethanol preservation significantly increased δ15N by 0.8–1.7‰ relative to frozen control samples, regardless of species. Ethanol enriched δ13C of squid mantle tissue as well, but showed variable alterations in fish muscle compared with the control (lipids extracted by chloroform and methanol). An additional extraction treatment with 99.5% ethanol increased δ13C by 1.3–2.0‰ for squid, and by 0.3–1.3‰ for fish relative to the control, without a further shift of δ15N, and reduced the variability of δ13C alterations of fish muscle. After this treatment, both δ15N and δ13C of the controls could be estimated from the samples preserved in ethanol by fitting to regression lines with high correlation coefficients (r2>0.90). These results suggest that, with additional treatment, marine predator samples preserved in 70% ethanol are able to be used for stable isotopic analysis.
The photoresponse of chlorophyll a (Chl a) fluorescence and xanthophyll pigments to light was studied in the diatom Thalassiosira weissflogii with respect to various durations of dark storage. The light-limited slope (α) obtained from the electron transport rate (ETR) versus the irradiance curve remained steady, whereas the light-saturated rate (ETRmax) decreased gradually during dark storage. Consequently the light-saturation index (Ek=ETRmax/α) decreased with time, suggesting that cells acclimate to dark conditions. Dark-acclimated cells were exposed to light-dark conditions with varied silicate availability. The maximum quantum yield of PSII (Fv/Fm), as well as the changes in the α and the ETRmax, increased immediately to the maximum on the first day and decreased for the second half of the light exposure period. The ratio of diatoxanthin (DT) to the xanthophyll pigment diadinoxanthin (DD) and DT (DT/[DD+DT]) represents thermal dissipation behavior through non-photochemical quenching (NPQ). This study indicates that Fv/Fm and Ek are a good index to follow photoacclimation during a transition from continuous dark conditions to the L-D cycle of saturated light. This study also indicates that dark-acclimated T. weissflogii can acclimate to the growth irradiance by the enhancement of photosynthetic activity with changes in xanthophyll pigments, in relation to the dark duration and silicate availability. Such a response to light suggests that the vegetative cells of T. weissflogii could possibly proliferate at ports in the coastal zone on a global scale after ejection into high light environments from the darkness of a ship’s ballast water tank.
In this study, stable isotope probing was used to identify a bacterial community involved with bicarbonate fixation in the water just below the oxycline of the meromictic Lake Suigetsu, Japan. Water samples were incubated with 13C-labeled bicarbonate under either light or dark conditions. The identity of active bicarbonate-fixing bacteria was revealed by 16S rRNA gene clone library analysis of 13C-labeled DNA fractions. Bacterial clones closely related to the green sulfur bacterial genus Chlorobium were detected under light conditions. Clone sequences phylogenetically affiliated with the genera Arcobacter and Desulfocapsa were also detected under light conditions. In the dark incubation, clones belonging to the class Epsilonproteobacteria were detected. Clone sequences belonging to a clade containing the genus Thiomicrospira were also retrieved from dark incubation samples. These results indicated that phylogenetically diverse bacteria might fix CO2 in the water below the oxycline of Lake Suigetsu.
The mysids, Orientomysis spp., are common in shallow coastal waters and estuaries in Japan, and are reported to be one of the main prey items for juveniles of many commercially important fish species. Some studies have suggested that the seasonal dynamics of mysids are an important factor determining the biomass and production structure of demersal fish communities. In this study, seasonal variation in the population structure and reproductive traits of Orientomysis japonica Marukawa, 1928 were investigated in Tango Bay, the western part of Wakasa Bay, Japan, from April 2007 to April 2009. Mean densities at depths of 5 and 10 m were highest in spring (ca. 100 ind. m−2), decreasing drastically in early summer to nearly 0 ind. m−2. Juveniles and immature individuals dominated the population (>80%) in spring and decreased in summer (<50%). Brooding females were captured year-round with mean body lengths ranging from 6.9 (August 2007) to 13.1 mm (February 2008). Body lengths of brooding females were negatively correlated with temperature. Brood size ranged from 1 to 102 and increased with female body length. The body sizes of all embryonic/larval stages within the marsupium were also negatively correlated with temperature. These results suggest that numerous large offspring released by the highly reproductive overwintering generation led to density increases and the maintenance of a high population density, while conversely, the summer–autumn generation exhibited repetitive short-term reproduction under high temperatures.
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