9:45 AM - 10:00 AM
[BCG07-04] Survival of tropical larger foraminifera in the Japan Sea during the snowy midwinter season
Keywords:foraminifera, Japan Sea
Tropical largeer foraminifera are the third most important organism forming the calcareous substrate of tropical coral reefs, and are important as ecosystem engineers in such region. The tropical larger foraminiferal genus Amphistegina is widely distributed in the southern part of the Japan Sea. The northern limit of living Amphistegina is located at the Oki Dogo Island and the eastern limit is in Hokuriku district. The critical temperature for Amphistegina has been said to be 14°C in winter. Needless to say, the winter climate of this area is characterized by heavy snow owing to winter monsoon. Therefore, the possibility of invalid distribution has been pointed out on the Japan Sea population.
In this study, scuba investigation was conducted on 12/Feb 2025 at Nonami, Shimanecho, Matsue City, Shimane Prefecture. Sea bottom samples, mainly composed of calcareous algae and sediments, were collected in the 5 cm squared area (25 cm2) on the rocky reef. Each sample was colored by Rosebengal, washed up to remove extra color and dried up. Then, foraminiferal individuals were picked up from the dried residues by using a binocular microscope.
Five samples were collected from 3.8 to 5.8 m in deep. The water temperature was 11℃ during the survey. The maximum population density was 390 individuals / 25cm2 at 4.0 m deep. This is the second abundant species in total living foraminifera. The maximum size of foraminiferal shell is ranged from 382 to 1667 μm. The remarkable abundance of Amphistegina during the snowy mid-winter and the presence of small immature individuals indicate that Amphistegina has already get a successful position in the Japan Sea.
In this study, scuba investigation was conducted on 12/Feb 2025 at Nonami, Shimanecho, Matsue City, Shimane Prefecture. Sea bottom samples, mainly composed of calcareous algae and sediments, were collected in the 5 cm squared area (25 cm2) on the rocky reef. Each sample was colored by Rosebengal, washed up to remove extra color and dried up. Then, foraminiferal individuals were picked up from the dried residues by using a binocular microscope.
Five samples were collected from 3.8 to 5.8 m in deep. The water temperature was 11℃ during the survey. The maximum population density was 390 individuals / 25cm2 at 4.0 m deep. This is the second abundant species in total living foraminifera. The maximum size of foraminiferal shell is ranged from 382 to 1667 μm. The remarkable abundance of Amphistegina during the snowy mid-winter and the presence of small immature individuals indicate that Amphistegina has already get a successful position in the Japan Sea.