01-05 December 2025
INCOIS, Hyderabad, India.
| Abstract Submission No. | ABS-06-0125 |
| Title of Abstract | Patterns of Dinoflagellate Vertical Descent in the Indian Ocean: Distribution, Diversity, and Ecological Factors |
| Authors | Aparna Mol T A*, Dr. Jagadish S Patil, Pranoy Paul, Dr. Samir Damare |
| Organisation | CSIR-National Institute of Oceanography |
| Address | THITHARAYIL HOUSE, KARINILAM P O, AMARAVATHY, KAPPILAMMOODU Kottayam, Kerala, India Pincode: 686513 E-mail: aparnamolta@gmail.com |
| Country | India |
| Presentation | Oral |
| Abstract | Dinoflagellates, key primary producers with diverse trophic strategies, remain unexplored beyond the epipelagic zone (0-200m). This study gives an account of the dinoflagellate vertical descent into various pelagic zones- epipelagic (0-200m), mesopelagic (200-1000m), bathypelagic (1000-4000 m) and abyssopelagic (>4000m) in the north eastern Indian Ocean (NEIO) and south tropical Indian Ocean (STIO). Using vertical hauls with multiple plankton nets (MPN), 156 microphytoplankton taxa (>100µm) were recorded, 83 species (53.2%) of which were dinoflagellates, with 20 autotrophic, 39 mixotrophic, 20 heterotrophic dinoflagellates (ATDs, MTDs, HTDs) and one unidentified species. These included 16 cyst-forming species, 69 thecates, 13 athecates and nine symbionts. Genus Tripos exhibited the highest diversity (36 species). Dinoflagellate abundance and diversity were highest in the epipelagic zone (77 species) and declined sharply with depth: mesopelagic (18), bathypelagic (13), and abyssopelagic zones (4). Of the epipelagic dinoflagellates, only a small portion descended deeper: in NEIO, 3.7% and 1.1% descend to the meso- and bathypelagic zones, respectively, whereas in STIO, 13.9%, 3.9% and 1.3% descend to the meso-, bathy- and abyssopelagic zones. Vertical patterns revealed dominance of athecate and thecate dinoflagellates in the epipelagic; athecate sharply declined below the epipelagic, and was completely absent in the abyssopelagic. Only structurally and physiologically adaptable taxa reached the deepest layer. Symbiotic dinoflagellates were limited to the epipelagic, possibly due to a symbiotic depth barrier and reliance on photosynthetic symbionts requiring light. Overall, descent through the water column is filtered by environmental (temperature, salinity, light intensity, density) and biological factors such as grazing. They select dinoflagellate taxa based on their morphological and ecological traits. This ⿿Pelagic Zone Filtration⿿ limits the descent of delicate and morphologically complex species. This study highlights the dinoflagellate descent pattern and the supporting factors influencing them to descend to deeper depths of the IO. |
| Are you part of IIOE-2 endorsed project | no |
| Keywords | Dinoflagellates, Indian Ocean, pelagic zone, thecate, athecate, symbionts, pelagic filters |
| For Awards | yes |
| Date Of Birth | 19-04-1996 |
| ECSN Registration Number | IIOE2-ECSN-0113 |