To evaluate the water purification function of the Manila clam Ruditapes philippinarum on the Rokujo tidal flat at the mouth of the Toyo River in Mikawa Bay, we calculated the nutrient budget using box model analysis in June. In addition, we investigated the biomass and growth of the juvenile Manila clam population and discuss the mechanism of nitrogen cycling in the tidal flat. The results of the box model analysis indicated that the removal rate of particulate organic nitrogen (PON) was 18.5 mgN・m^-2・h^-1 and the elution of dissolved total nitrogen (DTN) was 6.3 mgN・m^-2・h^-1. The total nitrogen (TN) removal rate was accordingly 12.2 mgN・m^-2・h^-1. In comparison to previous studies, the removal rates of PON and TN for the Rokujo tidal flat were larger than those of other tidal flats in Ise-Mikawa Bay. In terms of nitrogen cycling in the Rokujo tidal flat, it is suggested that the large juvenile Manila clam population enhances the removal of PON, and that their high gross-growth efficiency lowers the DTN returned to the water column of the tidal flat. Additionally, it is considered that DTN is rapidly absorbed by seaweeds or benthic microalgae. These mechanisms thus contribute to the high removal of both PON and TN in the Rokujo tidal flat. In order to facilitate ecosystem restoration of coastal bay estuaries, it is necessary to promote the restoration of tidal flats in river mouths, where primary production is high and red tides frequently occur.

To determine the accurate period for mass spawning of Acropora coral in the Sekisei Lagoon, Ryukyu Islands, the relationship between observations of spawning and slicks and lunar phase, as well as accumulated water temperature and solar radiation, was studied. Spawning was most often observed 3 days before to 2 days after the full moon in May.Most spawning occurred between 1 and 4 h after sunset and between -1.0 and 4.5 h of the high tide. All spawning occurred at a water temperature of 26°C in May, 2 to 3 months before the peak. The conditions of mass spawning in the Sekisei Lagoon was estimated to occur at a water temperature and solar radiation of >1.2×10³°C and 0.6×10³MJ·m^-2, respectively. The most probable period of spawning is around and on the full moon in May.

A tidal current calendar for the coastal area off Cape Soya in Hokkaido, Japan, has been used by fishermen of the drift fishery for giant Pacific octopus, Enteroctopus dofleini, since 2009. In the present study, the accuracy of suitable surface current velocities described in the calendar was verified and changes in drift-fishing activities resulting from the introduction of the calendar were clarified. A regression tree analysis of surface velocity measurements recorded by high-frequency ocean radar stations in the Soya region and the catch(kg・boat^-1・day^-1)showed that the catch increased when the surface velocity was in the range of 0.1 to 1.0 kt. Surface velocities were simulated based on tidal currents and the mean velocity of the Soya Warm Current. A correlation coefficient of 0.79 was obtained between the observed velocity and the simulated velocity. After the introduction of the calendar, the proportion of actual fishing days to possible fishing days(Fishing Effort Index)for fishermen who fished ≥50 days per year decreased. Most fishermen did not go fishing on days considered unsuitable for drift fishing after the introduction of the calendar.