Activity of sit-and-wait predator, red-spotted groupers (Epinephelus akaara), was measured using acoustic acceleration transmitters, AccelTag (Thelma Biotel, Trondheim, Norway). Nine red-spotted groupers tagged with the transmitters were released into a fish tank. The transmitter signal intervals derived from acceleration measured were recorded on acoustic receiver for 1 hour for each individual. At the same time, the fish behaviors were recorded using video cameras. The tail beat frequency of the tagged fish was counted as indicator of fish activity. We compared transmitter signal intervals and tail beat frequency. Our results showed that signal intervals distinguished whether red-spotted groupers moved their tail fin or not, suggesting that acoustic acceleration transmitter could detect the activity of red-spotted groupers. Acoustic telemetry with acceleration transmitter will be useful to apply to other sit-and-wait type predators to understand their movement patterns and activity rhythms.
To understand the effect of plate coupling on very low-frequency event (VLFE) activity resulting from megathrust earthquakes, we performed long-term multi-scale earthquake-cycle simulations (including a megathrust earthquake and slow earthquakes) on a 3-D subduction-plate boundary model, based on a rate- and state-dependent friction law. Our simulation suggests that the quiescence of shallow VLFEs off Miyagi may be explained by the location in the shallow-central part of the 2011 Tohoku earthquake because of the locally strong coupling, while observed activation of VLFEs off Iwate (northern part of Tohoku district), Fukushima (southern part of Tohoku district), and Ibaraki (northern part of Kanto district) are explained by the location on the outer rim. We also calculate the time series of hydraulic pressure data at DONET, comparing with the leveling change expected from our numerical simulation of the 1944 Tonankai earthquake. Since leveling change due to shallower VLF swarms is so local as to be incoherent, removal of the moving-averaged data from the data stacked by four nearby observation points in the same node may be useful to detect the short-term local leveling change. However, we need collaboration between seismology, geology, meteorology and tsunami engineering in order to separate components of crustal deformation, ocean fluctuation due to Kuroshio and instrumental drift from raw data of hydraulic pressure gauge on the seafloor around the source regions of megathrust earthquakes along Nankai Trough.
A laboratory experiment was conducted to obtain the physiological data of filter-feeding sessile organisms, Mytilus galloprovinciallis, Crassostrea gigas, Fistulobalanus albicostatus and Styela plicata, dominated on seawalls in the pacific coast of Japan. Clearance, faecal egestion and ammonia excretion rates of each species were measured at a constant food (phytoplankton; Skeletonema costatum) concentration, with manipulating two factors, water temperature and body mass. The relationships between those rates and the factors were represented by a set of common equation. The result of regression analysis showed that each rate was significantly correlated with water temperature or body mass. Absorption efficiencies unrelated to both water temperature and body mass, were estimated to be 69.5% for M. galloprovinciallis, 59.4% for C. gigas, 64.2% for F. albicostatus and 24.0% for S. plicata in average. Clearance rates, furthermore, were represented by the two kinds of equations, namely CR1 and CR2 as the functions of both factors. Analysis of differences between the observed and predicted values suggested that the CR2 gives more reliable estimates for clearance rates of the filter-feeding organisms. This study provides important parameters for nitrogen budget of sessile organisms inhabiting on seawalls and the effects on the coastal marine environments.
We investigated radiocesium concentrations in sediments and in Manila clams Ruditapes philippinarum. The samples were taken from three points in Tokyo Bay on September 2014. The ranges of radiocesium concentration in sediments were <0.35～0.59 Bq/kg-dry of 134Cs and 1.2～1.9 Bq/kg-dry of 137Cs. Each highest value was obtained from the most inside point of the bay. The ranges of radiocesium concentration in Manila clams Ruditapes philippinarum were <0.091 Bq/kg-wet of 134Cs and 0.13～0.16 Bq/kg-wet of 137Cs. The highest value of 137Cs in Manila clam also was obtained from the most inside point of the bay. Radiocesium concentrations in Manila clam living in Tokyo Bay are in safe level as a food. These data suggested that the level of radiocesium in the sediment affected that of Manila clam. In order to assess the risk of radiocesium in ecosystem of Tokyo Bay after the Fukushima Daiichi Nuclear Power Station (FDNPS) accident, we need to know accurate concentration of radiocesium (134Cs, 137Cs) in Manila clam. We estimated 134Cs concentrations of Manila clam by using 137Cs concentrations of that and 134Cs/137Cs activity ratio of FDNPS in that time. The estimated concentrations of 134Cs in Manila clam were in 0.042～0.051 Bq/kg-wet. There was no discrepancy between the measured concentration value and the estimated one. It is considered that this estimation method is useful in case of low level radiocesium.