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Mombetsu, Japan

Kajihara R.,Hokkaido University | Komorita T.,Hokkaido University | Komorita T.,Prefectural University of Kumamoto | Hamada A.,Hokkaido University | And 3 more authors.
Plankton and Benthos Research | Year: 2010

The small gastropod, Lacuna decorata Adams, living on macrophytobenthos or surface sediment, is one of the most dominant species of macrozoobenthos in Hichirippu lagoon covered with seagrass and macroalgae, eastern Hokkaido, Japan. We measured the standing stocks of primary producers and macrozoobenthos, and determined the stable carbon and nitrogen isotope ratios of the primary producers and L. decorata. With these results, we identify the main food items for L. decorata and discuss the feeding strategy of the small gastropod. This gastropod occupied about 64% in density and about 25% in biomass of the macrozoobenthos at all six sampling stations in the lagoon. It occurred densely on the surface of the sediment with dense patches of benthic microalgae (BMA), which contained extremely high levels of Chl.-a between 84 to 226 mg m -2 throughout the period of this study. Nevertheless, the stable isotope signatures of carbon and nitrogen of this gastropod clearly show the direct utilization of organic matter derived from seagrass, Zostera japonica, in the areas where the seagrass luxuriated. However, it shows also a flexible feeding strategy in food preference. It fed green algae such as Ulva pertusa and Urospora wormskioldii in the areas where the seagrass grew scarcely. © The Japanese Association of Benthology. Source

Komorita T.,Ehime University | Komorita T.,Hokkaido University | Kajihara R.,Hokkaido University | Tsutsumi H.,Prefectural University of Kumamoto | And 4 more authors.
Journal of Experimental Marine Biology and Ecology | Year: 2010

Previous estimations of nutrient mineralization in the water column by infaunal bivalves might have been overestimated because of underestimation of the uptake process by microphytobenthos in the field. We conducted field surveys of environmental conditions and quantitative sampling of Ruditapes philippinarum in a shallow lagoon system (Hichirippu Lagoon, eastern Hokkaido, Japan) in August 2006. We recorded the spatial distribution pattern and the molar ratio of dissolved inorganic nutrients to determine the limiting nutrients for microphytobenthos, to evaluate the input and output of nutrients at the entrance of the lagoon station, and to estimate potential nutrient mineralization by R. philippinarum. Our aim was to reevaluate the nutrient mineralization process by infaunal bivalve species. In this study, the mean standing stock of microphytobenthos inhabiting surface sediment (5 mm thick) on the tidal flats was 100 times higher than that of phytoplankton (1 m depth). Low N/P and high Si/N ratios (mean = 2.6 and 17.6, respectively) near the entrance of the lagoon compared to those of microphytobenthos (N:P:Si = 10.1:1:18) clearly suggest N deficiency. The flux of NH 4-N coming into the lagoon was 3.4 kmolN d - 1, and the flux out was - 3.7 kmolN d - 1. Thus, assuming that there would have been no phytoplankton and microphytobenthos uptake during the day, 0.3 kmolN d - 1 of NH 4-N was produced within the lagoon. However, the NH 4-N mineralization rate of the clams has been estimated to be approximately 7.7 ± 6.8 kmolN d - 1. Thus, 96% (7.4 kmolN d - 1, i.e., 7.7 kmolN d - 1 minus 0.3 kmolN d - 1) of the NH 4-N mineralized by the clam was consumed by microphytobenthos. In contrast, if all the NH 4-N inflow (3.1 kmolN d - 1) was consumed by the microalgae before outflow, 52% (4.0 kmolN d - 1, i.e., 7.7 kmolN d - 1 minus 3.7 kmolN d - 1) of the NH 4-N mineralized by the clams should have been consumed by microphytobenthos. Microphytobenthos on the tidal flats (11.3 ± 11.8 kmolN) used all of the surplus nutrients (between 4.0 and 7.4 kmolN d - 1), and the temporal division rate [=(NH 4-N uptake)/(standing stock of microphytobenthos)] of microphytobenthos would have to be between 0.35 and 0.65 d - 1. Residual NH 4-N (0.3 - 3.7 kmolN d - 1) was the water-column source and accounted for 12-148% of NH 4-N in the water column near the entrance of the lagoon (2.5 ± 1.4 kmolN) per day. This is the first field-based observation with a quantitative evaluation of nutrient mineralization by infaunal bivalves and nutrient uptake by microphytobenthos. © 2009 Elsevier B.V. All rights reserved. Source

Sakurai I.,Tokai University | Nakayama T.,Hokkaido Government Kushiro General Subprefectural Bureau | Hada Y.,Hokkaido Research Organization Central Fisheries Institute | Maekawa K.,Lake Saroma Fisheries and Aquaculture Co operation Organization | And 3 more authors.
Nippon Suisan Gakkaishi (Japanese Edition) | Year: 2014

We examined a suitable site for the growth and survival of juvenile Japanese littleneck clam Ruditapes philippinarum. The survey was conducted in three artificial clam nurseries constructed along the intertidal coastline of Lake Saroma, Hokkaido. Cages accommodating the juveniles were embedded in the offshore side of nurseries 1, 2, and 4 in April; then, juvenile growth was investigated after 6 months. The proportion of the juveniles that would be dislodged from the sand by bottom disturbance due to wave action was calculated using a simulation model. Caging experiments revealed that the offshore side of nursery 1 was suitable for achieving high shell growth. The simulation suggested that the survival rate of the juveniles was higher towards the offshore side of the nurseries. On the basis of the results, we hypothesized that the offshore side of nursery 1 would be suitable for the growth and survival of the juveniles. Around 18,000 juveniles were released in the offshore and land sides of nurseries 1 and 4. Mean shell length and survival rate of the juveniles in nursery 1 was 1.7 and 4.4 times as high as that in nursery 4 after 12 months of releasing; this result supported our hypothesis. Source

Komorita T.,Hokkaido University | Komorita T.,Prefectural University of Kumamoto | Tsutsumi H.,Prefectural University of Kumamoto | Kajihara R.,Hokkaido University | And 6 more authors.
Marine Ecology Progress Series | Year: 2012

We conducted field surveys to determine spatio-temporal variations in the water quality (including inorganic nutrient concentration) of a coastal lagoon, Hichirippu Lagoon (3.56 km 2), in Hokkaido, Japan. During a typical supply period (winter), a 24 h continuous survey was conducted to evaluate nutrient supply from the open ocean and examine nutrient utilization by microphytobenthos (MPB) based on the mass balance of a biophilic element. During February 2008, the majority of NO 3+NO 2-N was supplied from the open ocean, and the dissolved inorganic nitrogen (DIN) budget was 3.25 kmol N d -1. In March 2008, the total amount of organic nitrogen was 39.0 to 588 kmol N for MPB in the surface sediment (depth, 0.5 cm). Assuming that MPB in the surface sediment used all NO 3+NO 2-N input (3.93 kmol N d -1), their temporal division rate (NO 3+NO 2-N uptake/total amount of MPB) would be 0.01 to 0.10 d -1. Here the annual DIN budget was estimated to be 258 kmol N yr -1, which mainly depended on MPB-fixed oceanic DIN during winter. © 2012 Inter-Research. Source

Suga N.,Hokkaido University | Kajihara R.,Hokkaido University | Shibanuma S.,Hokkaido University | Yamada T.,Nishimuragumi Co. | Montani S.,Hokkaido University
Plankton and Benthos Research | Year: 2011

We conducted field sampling in a subarctic shallow lagoon (Hichirippu Lagoon) in the eastern part of Hokkaido, Japan. We investigated the chemical composition of the water column, sediment, and sinking particles collected by the sediment trap. The standing stock of chlorophyll a (Chl-a) in the water column and surface sediment were 0.4 to 9.3 and 35.9 to 184 mgm -2, respectively. Using stable isotope analysis, the contribution rate of microphytobenthos to the sinking particles was found to range from 63 to 74%. The average Chl-a content in the sinking particles was significantly lower than that of the water column. Our results suggest that the contribution of phytoplankton present in the water column to the Chl-a collected in the traps is likely to be negligible. We assumed that the Chl-a fluxes obtained in this study were microphytobenthic resuspension fluxes. The daily flux of Chl-a accounted for 47.0 to 1,270% of the total standing stock of Chl-a in the water column. The mean relative percentage of daily Chl-a flux divided by the standing stock of Chl-a in the sediment was 6.5%, which indicates that approximately 7% of the microphytobenthos present in the sediment was resuspended, and 93% of the total succeeded at escaping the winnowing action. Although the resuspension phenomenon had little effect on the population of microphytobenthos, the resuspended microphytobenthos had a major impact on the total micro algal biomass in the water column. This is the first direct estimate of microphytobenthic resuspension flux in shallow estuaries. © The Japanese Association of Benthology. Source

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