01-05 December 2025
INCOIS, Hyderabad, India.
| Abstract Submission No. | ABS-06-0189 |
| Title of Abstract | Phytoplankton dynamics in the Eastern Indian Ocean: physiological and genetic diversity and remaining challenges |
| Authors | Hiroaki Saito*, Fuminori Hashihama, Siyu Jiang |
| Organisation | The University of Tokyo |
| Address | 5-1-5 Kashiwanoha Kashiwa, Chiba, Japan Pincode: 2778564 E-mail: hsaito@aori.u-tokyo.ac.jp |
| Country | Japan |
| Presentation | Oral |
| Abstract | One of the key remaining scientific issues on marine food-web and biogeochemical cycles is the mechanisms of phytoplankton dynamics in oligotrophic oceans. The broad area of the planet is characterized by high temperature and low nutrient concentration, also known as ocean desert. Most global ecosystem models reproduce the region as a stable system with small variations in nutrient and phytoplankton concentration. However, recent monitoring studies revealed that the area showed large seasonal and annual variations in phytoplankton composition and productivity, which influence the biological carbon pump, stoichiometry, and production of higher trophic levels. We do not have enough knowledge to explain the variations. The eastern Indian Ocean is one of the oligotrophic regions on the planet. We conducted a meridional research cruise on board R/V Hakuho Maru along 88°E from the Bay of Bengal to the southern Indian Ocean and examined phytoplankton community structure, functional genes of Prochlorococcus, and their physiological response to nutrient supply. As expected, physical oceanographic perturbations, such as the Wyrtki Jet and mesoscale eddies, influence the nutrient supply and phytoplankton biomass. One surprise was the growth of phytoplankton, especially for Prochlorococcus, was not limited by nutrients even depleted nitrogenous nutrients throughout the region. We also found the size, division rate and chlorophyll production rate were highly variable along the transect. Shotgun genome sequencing of Prochlorococcus revealed the significant difference in functional gene composition, such as nitrate/nitrite reduction and iron complex transport along the transect. The present study shows that the Eastern Indian Ocean is not uniform at all in terms of the functional composition of phytoplankton and biogeochemical cycles. In the presentation, we will compare the ecosystems in the Eastern Indian Ocean and the Pacific Ocean and discuss the remaining issues in order to understand the dynamics of oligotrophic ecosystems. |
| Are you part of IIOE-2 endorsed project | yes |
| Endorsed Project Number | IIOE2-EP36 |
| Keywords | nutrient, phytoplankton, Prochlorococcus, biogeochemical cycle, |
| For Awards | no |