Underwater observations of the giant spoon worm <Emphasis Type="Italic">Ikeda taenioides</Emphasis> (Annelida: Echiura: Ikedidae) in a subtidal soft-bottom environment in northeastern Japan,which survived tsunamis of the 2011 off the Pacific Coast of Tohoku Earthquake

Tsunamis associated with the 2011 off the Pacific Coast of Tohoku Earthquake seriously disrupted the shallow marine ecosystem along a 2000 km stretch of the Pacific coast of Japan. The effects of the 2011 tsunamis on the soft-bottom benthic community have been relatively well studied in the intertidal zone, whereas tsunami effects on the subtidal benthos remain poorly understood. Here, we investigated populations of the world’s largest spoon worm Ikeda taenioides (Annelida: Echiura: Ikedidae) in subtidal zone of Funakoshi Bay, Tohoku District, northeastern Japan. Subtidal scuba-diving surveys at two sites in the bay showed extremely long proboscises frequently extending from small holes in the sandy seafloor shortly before and soon after the tsunami disturbances. Based on morphological and molecular identification, the proboscises were revealed to be parts of I. taenioides. On 30 November 2011, 265 days after the tsunami event, many large-sized individuals with >1 m long proboscises were observed; these individuals were probably not derived from post-tsunami larval recruitment but more likely survived the tsunami disturbances. This is surprising because other sympatric megabenthos (e.g. spatangoid echinoids and venerid bivalves) and seagrass beds were almost completely destroyed (although they later recovered) by the tsunamis in this bay. The burrows of I. taenioides are known to be very deep (70–90 cm), which may have sheltered them from the impacts of the tsunamis. Our observations suggest that the effects of the 2011 tsunamis on benthos in soft sediments may differ depending on their burrowing depth.     

Size fraction and class composition of phytoplankton in the Antarctic marginal ice zone along the 140°E meridian during February–March 2003

We investigated the size fraction and pigment-derived class compositions of phytoplankton within the euphotic zone of the Antarctic marginal ice zone between 63.3°S and 66.5°S along the 140°E meridian on two consecutive cruises in the late austral summer and early austral autumn of 2003. We observed significant temporal and spatial variations in phytoplankton size and taxonomic composition, although chlorophyll a concentrations were generally below 1 μg l⁻¹ during both periods. Microphytoplankton (>20 μm), mainly diatoms, were prominent in the euphotic zone in the southernmost area around 66.5°S during late summer. In the rest of the study area during both cruises, the phytoplankton community was dominated by pico- and nano-sized populations (<20 μm) throughout the euphotic zone. The small-size populations mostly consisted of diatoms and haptophytes, although chlorophytes were dominant in extremely cold water (−1.5°C) below the overlying warm water around 65.5°S during late summer. From late summer to early autumn, chlorophytes declined in abundance, probably due to increasing temperature within the euphotic zone (−1 to 0°C). These pico- and nano-phytoplankton-dominated populations were often accompanied by relatively high concentrations of ammonium, suggesting the active regeneration of nutrients within the small-size plankton community.     

Spatial and temporal distributions of water temperature in aSargassum forest

The present study examined the influence of aSargassum forest on the spatial and temporal distributions of water temperature in a small cove on a time scale of the order of hours. Water temperature and algal density were measured along a fixed transect at the cove for almost 2 days. The measurements were carried out in May 1977 during the season of luxuriant seaweed growth, and in August during the season of little growth. The average standing crop per unit volume, named the spatial algal density, was employed as a means of expressing the growth condition of the seaweed forest along the transect. Using the spatial algal density and by analyzing water temperature distribution the following facts were revealed. The diurnal fluctuation of water temperature was influenced by theSargassum forest during the season of luxuriant growth, and the seaweed forest delayed the ascent and descent of water temperature, especially under its canopy, on a time scale of the order of hours, i.e., the temperature distribution patterns were influenced by the heights and densities of theSargassum forest during its season of luxuriant growth. It is thought that these phenomena are brought about by two effects: one is the absorption by the seaweed forest of short-wave radiation passing through the sea surface, and the other is the suppression of convection by the seaweed.     

Measurements of vertical air temperature gradients with dipmeter

By means of measuring the dips of horizon with a Pulfrich dipmeter, vertical air temperature gradients near the sea surface were obtained with an accuracy of ca. ±0.01°C/m, much better than a conventional method with an array of temperature sensors. The additional advantage of this technique was that the measurements were made on board a ship underway, consequently data from wide oceanic areas could be accumulated rather quickly and easily. From the results of dip measurements at 125 stations on two cruises of the T/V Oshoro Maru of the Hokkaido University, extending from the Bering Sea to the south of Australia, the temperature gradients were computed with a new formula with an assumption that the refractive index of air varied with a height only. It was found that, in the northern North Pacific Ocean, vertical air temperature gradients were positive, while in the subtropical and tropical Pacific Ocean both the negative and positive gradients were observed. Generally, in the same sea region, the temperature profiles had the similar form, irrespective of air-sea temperature differences.     

Evidence for erosion and deposition by the 2011 Tohoku-oki tsunami on the nearshore shelf of Sendai Bay,Japan

Ongoing geological research into processes operating on the nearshore continental shelf and beyond is vital to our understanding of modern tsunami-generated sediment transport and deposition. This paper investigates the southern part of Sendai Bay, Japan, by means of high-resolution seismic surveys, vibracoring, bathymetric data assimilation, and radioisotope analysis of a core. For the first time, it was possible to identify an erosional surface in the shallow subsurface, formed by both seafloor erosion and associated offshore-directed sediment transport caused by the 2011 Tohoku-oki tsunami. The area of erosion and deposition extends at least 1,100 m offshore from the shoreline down to water depths of 16.7 m. The tsunami-generated sedimentological signature reaches up to 1.2 m below the present seafloor, whereas bathymetric changes due to storm-related reworking over a period of 3 years following the tsunami event have been limited to the upper ~0.3 m, despite the fact that the study area is located on an open shelf facing the Pacific Ocean. Tsunami-generated erosion surfaces may thus be preserved for extended periods of time, and may even enter the rock record, because the depth of tsunami erosion can exceed the depth of storm erosion. This finding is also important for interpretation of modern submarine strata, since erosion surfaces in shallow (depths less than ~1 m) seismic records from open coast shelves have generally been interpreted as storm-generated surfaces or transgressive ravinement surfaces.     

Introduction of geospatial perspective to the ecology of fish-habitat relationships in Indonesian coral reefs: A remote sensing approach

Coral reef ecosystems worldwide are now being harmed by various stresses accompanying the degradation of fish habitats and thus knowledge of fish-habitat relationships is urgently required. Because conventional research methods were not practical for this purpose due to the lack of a geospatial perspective, we attempted to develop a research method integrating visual fish observation with a seabed habitat map and to expand knowledge to a two-dimensional scale. WorldView-2 satellite imagery of Spermonde Archipelago, Indonesia obtained in September 2012 was analyzed and classified into four typical substrates: live coral, dead coral, seagrass and sand. Overall classification accuracy of this map was 81.3% and considered precise enough for subsequent analyses. Three sub-areas (CC: continuous coral reef, BC: boundary of coral reef and FC: few live coral zone) around reef slopes were extracted from the map. Visual transect surveys for several fish species were conducted within each sub-area in June 2013. As a result, Mean density (Ind. / 300 m²) of Chaetodon octofasciatus, known as an obligate feeder of corals, was significantly higher at BC than at the others (p < 0.05), implying that this species’ density is strongly influenced by spatial configuration of its habitat, like the “edge effect.” This indicates that future conservation procedures for coral reef fishes should consider not only coral cover but also its spatial configuration. The present study also indicates that the introduction of a geospatial perspective derived from remote sensing has great potential to progress conventional ecological studies on coral reef fishes.

     

Tidally oscillating bisulfide fluxes and fluid flow rates observed with in situ chemical sensors at a warm spring in Monterey Bay,California

An In Situ Ultraviolet Spectrophotometer (ISUS) was coupled to a benthic chamber to characterize the bisulfide flux emanating from a warm spring at the Extrovert Cliff locality within Monterey Bay, California. The chamber was periodically flushed with bottom seawater to reset chemical concentrations, which enabled deployments over multiple days. Data from several deployments, each lasting at least 10 days, were used to calculate flow rates, fluid concentrations, and fluxes over time. The bisulfide concentration of the fluid entering the chamber varied from 75 to 4500 μmol l^?1. Positive temperature anomalies up to 3.5° were associated with these elevated concentrations. Linear flow rates ranged from 2 to >17 m day^?1, while the bisulfide fluxes varied from 0.2 to 80 mol m^?2 day^?1. The bisulfide originated at depth and was not produced in the surface sediments via an anaerobic oxidation of methane coupled to sulfate reduction. Tides modulated the flow as well as the composition of the fluid entering the chamber. It appeared that a deep sourced fluid, which supplied the bisulfide, was mixed with a second, ambient seawater-like fluid before entering the flux chamber. At low tides, flow rates were at their highest and the contribution of the deep sourced fluid to the fluid entering the chamber was at a maximum.     

Energy balance above a boreal coniferous forest: a difference in turbulent fluxes between snow‐covered and snow‐free canopies

To evaluate the interactive effects of snow and forest on turbulent fluxes between the forest surface and the atmosphere, the surface energy balance above a forest was measured by the eddy correlation method during the winter of 1995–1996. The forest was a young coniferous plantation comprised of spruce and fir. The study site, in Sapporo, northern Japan, had heavy and frequent snowfalls and the canopy was frequently covered with snow during the study period. A comparison of the observed energy balance above the forest for periods with and without a snow‐covered canopy and an analysis using a single‐source model gave the following results: during daytime when the canopy was covered with snow, the upward latent heat flux was large, about 80% of the net radiation, and the sensible heat flux was positive but small. On the other hand, during daytime when the canopy was dry and free from snow, the sensible heat flux was dominant and the latent heat flux was minor, about 10% of the net radiation. To explain this difference of energy partition between snow‐covered and snow‐free conditions, not only differences in temperature but also differences in the bulk transfer coefficients for latent heat flux were necessary in the model. Therefore, the high evaporation rate from the snow‐covered canopy can be attributed largely to the high moisture availability of the canopy surface. Evaporation from the forest during a 60‐day period in midwinter was estimated on a daily basis as net radiation minus sensible heat flux. The overall average evaporation during the 60‐day period was 0·6 mm day⁻¹, which is larger than that from open snow fields. Copyright © 1999 John Wiley & Sons, Ltd.     

Suspended sediment discharge in subsurface flow from the head hollow of a small forested watershed,northern Japan

Surface flow and suspended sediment discharge from the head hollow of the Jozankei Experimental Watershed in Hokkaido, northern Japan, were measured to clarify the implications of subsurface hydrology for soil movement. Subsurface discharges during the extremely large storms of 1993 to 1994 were measured in a V-notch weir installed at a natural spring near the bottom of the head hollow, and shallow groundwater levels were observed in the wells excavated in the hollow. Sediment samples whose particle size range from 0·001 to 0·1 mm were manually and automatically collected at 15 to 60 min intervals, by use of 1 or 21 polyethylene bottles. Maximum concentration and flux of suspended sediment during the storms preceded the peak discharge of subsurface flow by several hours. Neither the changes in concentration (mg l⁻¹) nor flux (mg s⁻¹) of suspended sediment coincided with those in subsurface discharge (l s⁻¹). Furthermore, sediment concentration was poorly correlated with the rate of change in subsurface discharge (l s⁻²) during the rising limb of the hydrograph. Suspended sediment flux during the acceleratory limb, however, was closely correlated with the rate of change in subsurface discharge. The relationship between suspended sediment flux and rate of change in subsurface discharge were in inverse proportion to initial subsurface discharge before the storm runoff and they represented rare seasonal variation. Subsurface hydraulic erosion and transport of suspended sediment resulting from changes in rate of change in subsurface discharge actively occur during the acceleratory rising limb of the hydrograph. Accordingly, subsurface hydraulic erosion during the acceleratory rising limb of the hydrograph can be physically understood by analysing suspended sediment flux associated with rate of change in subsurface discharge and initial subsurface discharge. © 1997 John Wiley & Sons, Ltd.     

Temporal variation in phytoplankton composition related to water mass properties in the central part of Sagami Bay

Temporal variations in water mass properties and the composition of phytoplankton pigments in the central part of Sagami Bay were investigated by monthly observations from June 2002 to May 2004. Eleven pigments were quantified using high-performance liquid chromatography (HPLC) from 100%, 20%, and 5% light depths relative to the surface; the class-specific composition of phytoplankton community was then obtained by CHEMTAX analysis. The study area was influenced by the Kuroshio water for most of the observation period. The mean contribution of diatoms in all samples was relatively low (29%), while that of flagellates, mainly chlorophytes or cryptophytes, was quite high (60%). The phytoplankton composition at the three depths was uniform throughout the observation period, indicating that the vertical structure of the phytoplankton community did not develop significantly over time. A distinct temporal pattern was observed: flagellates dominated during the summer of 2002 and the winters of 2002–2003 and 2003–2004, while diatoms dominated during the summer of 2003. This pattern was associated with water mass changes. The community in the summer of 2003 was influenced by coastal water. While no distinct spring bloom of phytoplankton was observed, a weak increase in chlorophyll a was observed during the spring of 2004. Ocean color satellite data showed that fluctuations in chlorophyll a concentrations at time scales much shorter than a month occurred during the spring of 2003 and that the elevations in chlorophyll a levels were not continuous. The fluctuations were probably associated with rapid flushing by the Kuroshio water, which has low chlorophyll a content.