Prey Composition and Prey Selectivity of an Intertidal Generalist Predator, Muricodrupa fusca (Küster) (Muricidae)

Abstract.  Natural prey composition and prey selectivity of the muricid snail Muricodrupa fusca (Küster), which forages on a wide range of prey, was investigated. Natural prey composition was evaluated through correcting the apparent diet (the result of observations of the feeding behavior) by the handling time, which was determined by laboratory analysis. The apparent diet and the natural diet should generally differ because prey items that require a longer handling time will be observed with higher frequencies. Multiple regression equations were derived to relate the handling time to prey size, predator size and water temperature. A large discrepancy in the apparent versus natural diet of M. fusca was found in prey species composition and prey size. They foraged on at least 11 species of sessile and mobile prey including six limpet species, and mainly preyed on Siphonaria spp. and Lottia spp. in the field. By comparing the percentage of the natural diet to that of prey abundance in the field, M. fusca preferred Siphonaria spp. and Lottia spp. and did not select the other prey species. The selectivity of this predator was explained by optimal foraging theory and antipredator defenses of some limpet species. The relationships among attacking methods, handling time and prey selectivity are also examined.     

Propulsion system with flexible/rigid oscillating fin

The purpose of this paper is to describe the feasibility research on an oscillating fin propulsion control system as a vehicle actuator. The system is designed and constructed in order to be combined with ship models. Tank cruising tests are conducted to confirm the system's feasibility. As a result, several advantages of the oscillating fin system are found. A neural network is successfully applied for an identification of the ship model with the oscillating fin, and its effectiveness is confirmed     

Moored floating breakwater response to regular and irregular waves

The simple, yet versatile numerical technique particularly suitable for investigating the problem of the wave attenuation by moored floating breakwater was recently developed by the author. In order to verift the theory, nearly full scale model tests were conducted in a large wave tank ($\text{3.6}\text{m wide}\text{× 4.5}\text{m high}\text{× 106}\text{m long}$). Both random waves and monochromatic waves were used to compare the results. A breakwater with a rectangular cross-section and a hydrodynamically shaped «three-cycle cylinderå breakwater were tested. Incident wave spectra were successfully decomposed from the multi-reflected sea spectra. Frequency response functions of transmitted wave, sway, heave and roll motions of the breakwater as well as mooring forces were all experimentally determined and compared with the theory. Generally, excellent agreements between the theory, the random wave tests and the monochromatic wave tests were obtained for the hydrodynamically shaped breakwater. Except near the modal frequencies of body motion generally good agreement between theory and experiment was obtained for the rectangular breakwater. Near the modal frequencies, the body motion was damped by the flow separation at the sharp corners of the rectangular breakwater. Generation of higher harmonics in wave, body motion and mooring forces was observed and measured, but was generally small. The slow drift oscillation and its effects on the performance of the spring moored breakwaters were also small. From the comaprisons of the small scale test and the large scale tests, it was found that the scale effects were negligibly small on the performance of the spring-moored breakwaters.     

Alkaline phosphatase activity and phosphatase hydrolyzable phosphorus for phytoplankton in hiroshima bay, Japan

We investigated the seasonal variability of free alkaline phosphatase activity in seawater and alkaline phosphatase hydrolysable phosphorus (APHP) at 3 stations in Hiroshima Bay using alkaline phosphatase extracted from the dinoflagellates Alexandrium tamarense and Gymnodinium catenatum. The dissolved inorganic phosphorus (DIP) was lower than 1 μM in all samples; the lowest values were in May. The amount of APHP was high at the surface and bottom waters of all stations in May, showing DIP-depleted conditions. In August and November, the amount of APHP was much less than the amount of APHP in May, indicating that the availability of dissolved organic phosphorus (DOP) for these species was low and/or uptake during the dinoflagellate blooming might have occurred in the area. The results obtained from short-term variations of AP activity might suggest that the growth of dinoflagellates in this season may be partly supported by the AP produced by other diatoms.     

Evolution of the composition of seawater through geologic time, and its influence on the evolution of life

The redox state of the surface environment of the early Earth is still controversial, and a detailed and quantitative estimate is still lacking. We carried out in-situ analyses of major, trace, and rare-earth elements of carbonate minerals in rocks with primary sedimentary structures in shallow and deep sea-deposits, in order to eliminate secondary carbonate and contamination of detrital materials, and to estimate the redox condition of seawater through time. Based on the Ce content and anomalies of the carbonate minerals at given parameters of atmospheric CO₂ content (pCO₂) and Ca content of seawater, we calculated the oxygen contents of shallow and deep seawater, respectively. The results show that the oxygen content of the deep sea was low and constant until at least 1.9 Ga. The oxygen content of shallow seawater increased after 2.7 Ga, but fluctuated. It became quite high at 2.5 and 2.3 Ga, but eventually increased after the Phanerozoic. In addition, the calculation of a high pCO₂ condition shows that seawater was more oxic even in the Archean than at present, suggesting a relatively low pCO₂ through geologic time.Our detailed calculations from compositions of carbonate minerals in Three Gorge area, south China show a low oxygen content of seawater after the Snowball Earth until the late Ediacaran, an increase in the late Ediacaran, and a significant decrease around the Precambrian–Cambrian and Nemakit/Daldynian–Tommotian boundaries. These variations were possibly caused by global regression and dissolution of methane hydrates.     

Observations of some oxygen-containing and sulfur-containing organic molecules in cold dark clouds

Observations of nine oxygen- and sulfur-containing organic molecules have been made toward the cold dark clouds TMC-1 and L134N. We have confirmed the presence of para-ketene (H2C2O) in TMC-1, have for the first time observed ortho-ketene, and find a total ketene column density approximately 1 x 10(13) cm-2. Thioformaldehyde (H2CS) is easily detectable in both TMC-1 and L134N, with a column density about 5 times larger in the former source (approximately 3 x 10(13) cm-2). The fractional abundance of ketene is comparable to the predictions of ion-molecule chemistry, while that of thioformaldehyde in TMC-1 is one to two orders of magnitude greater than that expected from such models at steady state. Interstellar sulfur chemistry thus continues to be poorly understood. We set upper limits for the column densities of formic acid (HCOOH), vinyl alcohol (CH2CHOH), methyl formate (HCO2CH3), formamide (NH2CHO), methyl mercaptan (CH3SH), isothiocyanic acid (HNCS), and thioketene (H2C2S) in both sources.     

Weathering rind formation in buried terrace cobbles during periods of up to 300ka

Weathering rinds formed in Mesozoic sandstone and basalt cobbles buried in terrace deposits for up to 300 ka have been investigated. The aim was to determine the formation process and elemental mass balances during rind development. The ages of terraces distributed in the western part of Fukui prefecture, central Japan have been determined as 50 ka, 120 ka and 300 ka based on a tephro-stratigraphic method. Detailed investigations across the weathering rinds, consisting of microscopic observations, porosity measurements, and mineralogical and geochemical analyses using X-ray diffractometry (XRD), X-ray fluorescence (XRF), secondary X-ray analytical microscopy (SXAM), scanning electron microanalyser (SEM) and electron probe microanalysis (EPMA) have been carried out. The results revealed that the Fe concentrations in the weathering rind of a basalt cobble slightly decreased from the cobble’s surface (rim) towards the unweathered core. In contrast, in a sandstone cobble formed under the same environmental conditions over the same period of time there is an Fe-rich layer at some distance below the cobble’s surface. Elemental mass balances across the rinds were determined by using open system mass balance (τ_i,j) calculations and show that the Fe was precipitated as Fe-oxyhydroxides in the basalt cobbles, although Fe was slightly removed from the rims. In sandstone cobbles, on the other hand, Fe migrated along a Fe concentration gradient by diffusion and precipitated as Fe-oxyhydroxide minerals to form the weathering rinds. Presumably, precipitation was due to the relatively higher pH conditions caused by mineral dissolution within the pores, principally involving calcite, but probably also silicates including feldspar. The detailed characterization of the weathering rinds revealed the influence of lithology on the accumulation and dissolution of Fe-oxyhydroxides, causing weathering rinds with different characteristics to develop in different kinds of buried cobbles under the same conditions. Relatively large climatic changes in the study area did not cause discernable variations in the mean formation rates of the studied rinds, which were in the order of 10^?8 m/a for both basalt and sandstone cobbles. These rates are 1–2 orders of magnitude slower than those reported for tropical areas elsewhere, most probably due to the lower rainfall in the studied area.     

Evolution of carbon dioxide-bearing saline fluids in the mantle wedge beneath the Northeast Japan arc

Lherzolite xenoliths containing fluid inclusions from the Ichinomegata volcano, located on the rear-arc side of the Northeast Japan arc, may be considered as samples of the uppermost mantle above the melting region in the mantle wedge. Thus, these fluid inclusions provide valuable information on the nature of fluids present in the sub-arc mantle. The inclusions in the Ichinomegata amphibole-bearing spinel–plagioclase lherzolite xenoliths were found to be composed mainly of CO₂–H₂O–Cl–S fluids. At equilibrium temperature of 920 °C, the fluid inclusions preserve pressures of 0.66–0.78 GPa, which correspond to depths of 23–28 km. The molar fraction of H₂O and the salinity of fluid inclusions are 0.18–0.35 and 3.71 ± 0.78 wt% NaCl equivalent, respectively. These fluid inclusions are not believed to be fluids derived directly from the subducting slab, but rather fluids exsolved from sub-arc basaltic magmas that are formed through partial melting of mantle wedge triggered by slab-derived fluids.     

Non-intrusive measurements of crater growth

An experimental technique to measure crater growth is presented whereby a high speed video captures profiles of a crater forming after impact obtained using a vertical laser sheet centered on the impact point. Unlike previous so called “quarter-space experiments,” where projectiles were launched along a transparent Plexiglas sheet so that growth of half a crater could be viewed, the use of the laser sheet permits viewing changes in crater shape without any physical interference to the cratering process. This technique indicates that for low velocity impacts (<300 m/s) into 220 μm glass beads that are without cohesion and where the projectile is not disrupted, craters initially grow somewhat proportionally, but that later their depths remain essentially constant while their diameters continue to expand. In addition, these experiments indicate that as the impact velocity increases, the rate of growth and the transient depth to diameter ratio at the end of ejecta excavation decreases. These last two observations are probably due to the large time of penetration of the projectile, which becomes a significant fraction of the time of crater formation. This is contrary to the expectations for the scaling rules, which assumes a point source. Very high curtain angles (>45°) are also seen, and could be due to the low friction angle of the target. Significant crater modification, which is rarely seen in “quarter-space experiments,” is also observed and appears to be controlled by the dynamic angle of repose of the target. These latter observations indicate that differences in target friction angles may need to be considered when determining near rim ejecta-mass distributions and large-scale crater modification processes on the planets.