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Kawamata S.,Japan National Research Institute of Fisheries Engineering
Journal of Experimental Biology | Year: 2012

Algal mats can hinder the adhesion of the tube feet of sea urchins. This leads to the hypothesis that the restriction of sea urchin feeding activity by wave action can potentially be enhanced by the presence of algal mats, which will facilitate the survival of kelp recruits at sites with wave action in urchin barrens. To evaluate the potential anti-attachment effect of algal mats on sea urchins, a laboratory tank experiment was performed on the movement of Strongylocentrotus nudus sea urchins and their grazing on juvenile kelp plants at the center of 30×30 cm flat test substrates with or without a thin-layer microalgal mat at four levels of oscillatory flow (maximum orbital velocity: 10, 20, 30 and 40 cm s -1). The grazing loss of kelp slightly increased with increasing velocity up to 30 cm s -1 in the absence of microalgal mats, while in contrast the loss substantially decreased at 30 cm s -1 in their presence. Sea urchins were dislodged more frequently at 20 cm s -1 or higher velocities in the presence of microalgal mats. Mats were frequently abraded by scraping by the adoral spines during urchin movement at high velocities (30 and 40 cm s -1) but were subject to no or only slight urchin grazing in most cases. The results indicate that the overall decrease in grazing loss of kelp within the microalgal mats was attributable to the anti-attachment effect on urchins during incursions rather than due to urchins grazing on the mats. © 2012. Published by The Company of Biologists Ltd. Source


Sudo H.,Japan National Research Institute of Fisheries And Environment of Inland Sea | Kajihara N.,Japan National Research Institute of Fisheries And Environment of Inland Sea | Noguchi M.,Japan National Research Institute of Fisheries Engineering
Marine Biology | Year: 2011

Although mysids play important roles in marine food chains, studies on their production are scarce, especially for warm-water species. We investigated life history and production of Orientomysis robusta in a shallow warm-temperate habitat of the Sea of Japan. Its spawning and recruitment occurred throughout the year; 19 overlapping cohorts were recognizable over an annual cycle. The summer cohorts recruited in July-September exhibited rapid growth, early maturity, small brood size, and small body size. A converse set of life history traits characterized the autumn-winter cohorts recruited in October-March. The spring cohorts recruited in April-June had intermediate characteristics of both cohorts. Life spans were 19-33, 21-48, and 69-138 days for summer, spring, and autumn-winter cohorts, respectively, and mortality rates were high for spring and summer cohorts, especially during June-August but were low for autumn-winter cohorts. Production calculated from the summation of growth increments was 488.8 mg DW m-2 year-1 with an annual P/B ratio of 21.26. The short life span seems to be responsible for such an extremely high P/B ratio. A method not requiring recognition and tracking cohorts gave similar values (534.0 mg DW m-2 year-1 and 20.49). The close agreement in production values between the two methods indicates our estimates are valid. © 2011 Springer-Verlag. Source


Rasmussen M.H.,University of Iceland | Akamatsu T.,Japan National Research Institute of Fisheries Engineering | Teilmann J.,University of Aarhus | Vikingsson G.,Iceland Marine Research Institute | Miller L.A.,University of Southern Denmark
Deep-Sea Research Part II: Topical Studies in Oceanography | Year: 2013

For the first time bio-logging tags were attached to free-ranging white-beaked dolphins, Lagenorhynchus albirostris. A satellite tag was attached to one animal while an acoustic A-tag, a time-depth recorder and a VHF transmitter complex was attached to a second dolphin with a suction cup. The satellite tag transmitted for 201 day, during which time the dolphin stayed in the coastal waters of western Iceland. The acoustic tag complex was on the second animal for 13. h and 40. min and provided the first insight into the echolocation behaviour of a free-ranging white-beaked dolphin. The tag registered 162 dives. The dolphin dove to a maximum depth of 45. m, which is about the depth of the bay in which the dolphin was swimming. Two basic types of dives were identified; U-shaped and V-shaped dives. The dolphin used more time in U-shaped dives, more clicks and sonar signals with shorter click intervals compared to those it used in V-shaped dives. The dolphin was in acoustic contact with other dolphins about five hours after it was released and stayed with these for the rest of the tagging time. Possible foraging attempts were found based on the reduction of click intervals from about 100. ms to 2-3. ms, which suggests a prey capture attempt. We found 19 punitive prey capture attempts and of these 53% occurred at the maximum dive depth. This suggests that more than half of the possible prey capture events occurred at or near the sea bed. © 2012 Elsevier Ltd. Source


Sugimatsu K.,Japan National Research Institute of Fisheries Engineering | Isobe A.,Ehime University
Journal of Oceanography | Year: 2011

From 1980 to 1995, in August, the bottom layer of Osaka Bay was occupied by cold, nutrient-rich water compared with that observed during both previous and subsequent decades. To investigate the mechanisms for the intrusion of bottom-layer cold water into Osaka Bay, the intrusion into Osaka Bay via the Kii Channel is simulated using a finite-volume coastal ocean model with unstructured triangular cell grids. The initial conditions, boundary conditions, and surface temperature given to the model are obtained from daily reanalysis data provided by the Japan Coastal Ocean Predictability Experiment. The model shows that cold water uplifted on the eastern side of the Kii Peninsula is propagated westward at 1.0 m/s as a coastal boundary current; it reaches the Kii Channel mouth when the Kuroshio axis is located around 74 km south of Cape Shionomisaki. However, the modeled cold water mass at the Kii Channel mouth does not intrude further to the north of the Kii Channel; therefore, another mechanism is required to explain the cold-water intrusion into the bottom layer of Osaka Bay. A plausible explanation is the estuarine circulation established by the freshwater supply at the bay head. When the river runoff is included in the model without forced vertical mixing, the temperature in Osaka Bay decreases 6.6 days later than the temperature decreases at the Kii Channel mouth. Furthermore, the shoreward current speed in the bottom layer of the modeled estuarine circulation is 15 cm/s, which provides the mechanism required for the cold water mass to pass the Kii Channel. © 2011 The Oceanographic Society of Japan and Springer. Source


Kawamata S.,Japan National Research Institute of Fisheries Engineering | Yoshimitsu S.,Kagoshima Prefectural Fisheries Technology and Development Center | Tanaka T.,Kagoshima Prefectural Fisheries Technology and Development Center | Igari T.,Kagoshima Prefectural Fisheries Technology and Development Center | Tokunaga S.,Kagoshima Prefectural Fisheries Technology and Development Center
Journal of Sea Research | Year: 2011

Sedimentation can provide indirect benefits to the survival of macroalgae in areas with potentially high grazing pressure. Field studies were performed in an embayment with extensive urchin barrens but also with locally persistent fucoid beds, on the coast of Kagoshima, south-western Japan, to elucidate the physical and biological processes responsible for the maintenance of the beds. Rocky subtidal reefs devoid of fine sediment were almost completely barren and dominated by sea urchins (primarily Echinometra sp. A), while fucoid algae (predominantly Sargassum duplicatum) densely populated cobble sites overlaid with a thin layer of fine sediment (medium grain size: 0.15-0.25. mm). Quadrat samplings in areas intermixed with urchin barrens and sand flats as well as experimental addition of sediment suggested that Echinometra sp. was readily excluded from hard substratum overlaid with even only a thin layer of fine sediment. Quadrat surveys and a transplant experiment conducted at the border area between a cobble bed with a thin cover of fine sediment and a sediment-free boulder one indicated that sea urchins (mainly composed of Echinometra sp. and Diadema spp.) rarely invaded the sediment-covered bed to graze. Wave measurements at the entrance (8. m deep) of the embayment over a 3.5-year period showed that the study area had long-term extremely calm conditions (84% of significant wave heights < 0.1. m) and seasonal or transient moderate disturbances due to relatively high waves (significant wave height: 0.8-1.3. m). However, the 2-year time series of root-mean-square wave orbital velocity estimates at different sites consistently suggested that the wave-action intensities at urchin barrens were still too high for deposition of fine sediments which occurred in more wave-sheltered persistent fucoid area. Nearly 2-year investigations on sediment level change and on cobble substrates together with overlying sediment in the fucoid area suggested that the absence of fatal sediment inundation and maintenance of the thin overlying sediment layer (mean thickness < ca 2. mm) throughout the year allowed settlement and growth of sand-tolerant fucoids by preventing urchin grazing. © 2011 Elsevier B.V. Source

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