No abstract

Seasonal changes in the composition and food habits ofˆsh communities in a Sargassum confusum-dominated bed oŠ the coast of Ishikari, Hokkaido, Japan were examined. Twenty-seven species, a total of 997 individuals, were collected by beach seine surveys from June 2002 to August 2003. Numbers of individuals and species increased in spring to fall compared to winter. A cluster analysis based on stomach contents composition showed that theˆsh communities comprised eight feeding groups: A) phytal amphipods, B) phytal and benthic amphipods, C) benthic polychaetes and phytal amphipods, D) phytal amphipods and isopods, E) benthic copepods and amphipods, F) planktonic copepods, G) phytal mysids and planktonic copepods, and H) phytal mysids feeders. Ontogenetic diet shifts were recognized in Pholidapus dybowskii, Aulichthys japonicus, Hexagrammos otakii and Syngnathus schlegeli, although Blepsias cirrhosus, Neozoarces steindachneri and Zoarchias veneˆcus were included in

We examined the characteristics of scour at the propagation grounds developed using sand-tube for

The growth of the small perennial seaweed assumed to be one of causes of isoyake is restrained by abrasion of the block surface every year. Large annual seaweed can be generated every year if the surface of the block is abraded by the suspended sediment of a high concentration by the rough seas during the winter month. The concrete block with different abrasion hardness was produced by mixing the desulfurizing agent with the fly ash cement by the concentration of 125kg/m3-500kg/m3. The developed block was set up in the surf zone of sand coast, consequently a positive correlation was admitted between the concentration of the suspended sediment and the production of the kelp Laminaria religiosa. In addition, the production of the kelp has quadrupled compared with a past concrete block.

We examined a suitable site for the growth and survival of juvenile Japanese littleneck clam Ruditapes philippinarum. The survey was conducted in three artiˆcial clam nurseries constructed along the intertidal coastline of Lake Saroma, Hokkaido. Cages accommodating the juveniles were embedded in the oŠshore 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 oŠshore 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 oŠshore side of the nurseries.On the basis of the results, we hypothesized that the oŠshore side of nursery 1 would be suitable for the growth and survival of the juveniles. Around 18,000 juveniles were released in the oŠshore 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.