Abstract
We studied the biodiversity of autotrophic calcareous coccolithophore assemblages at 30 locations in the Eastern Equatorial Indian Ocean (EEIO) (80°–94°E, 6°N–5°S) and evaluated the importance of regional hydrology. We documented 26 species based on the identification of coccospheres and coccoliths, respectively. The coccolithophore community was dominated by Gephyrocapsa oceanica, Emiliania huxleyi, Florisphaera profunda, Umbilicosphaera sibogae, and Helicosphaera carteri. The abundance of coccoliths and coccospheres ranged from 0.2 × 103 to 160 × 103 coccoliths l−1 and 0.2 × 103 to 68 × 103 cells l−1, averaged 23 × 103 coccoliths l−1 and 9.4 × 103 cells l−1, respectively. Biogenic PIC, POC, and rain ratio mean values were 0.50 μgC l−1, 1.047 μgC l−1, and 0.10 respectively. High abundances of both coccoliths and coccospheres in the surface ocean layer occurred on the north of the equator. Vertically, the great majority of coccoliths and coccospheres were concentrated in water taken from depths of <75 m. The ratios between the number of coccospheres and free coccoliths indicated that coccoliths experience different levels of dissolution when transported to deep water. Abundant coccolithophores mainly occurred at the west of 90°E, which is in accordance with the presence of Wyrtki jets. Patterns of coccolithosphores and of coccoliths have been reflected in hydrological processes.
Highlights
Coccolithophores are thrived in the photic water column
The coccoliths represented by G. oceanica, U. sibogae, H. carteri and H. hyalina were concentrated in the surface layer characterized by high temperature and low salinity
The coccolithophore assemblage in the eastern equatorial Indian Ocean (EEIO) during the spring intermonsoon season was primarily comprised of the coccoliths such as G. oceanica, E. huxleyi, U. sibogae, H. carteri, and H. hyalina and the coccospheres F. profunda, G. oceanica, E. huxleyi, U. irregularis, and U. sibogae based on dominance index
Summary
Coccolithophores are thrived in the photic water column. They are the unicellular microalgal flagellates with diverse life cycles that (alternating diploid - haploid stage) belongs to marine nanoplankton[1,2]. The increased concentration of CO2 used to combined with other factors (e.g., nutrient elements, pH, irradiance, temperature) and stimulate the fixation of cell organic carbon by photosynthesis, the effect diminishing the rain ratio of coccolithophores[16,17,18,19]. These calcifying nanoplankton are negatively affected by ocean acidification with decreased availability of carbonate, especially in colder water realms[20,21]. Our three main objectives were to (1) document the abundance, diversity and geographical patterns of living coccolithophores; (2) explain the variations occurring in nano flora assemblages; (3) correlate these variations to regional hydrographic parameters
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