[BBG01-P05] Bloom of Palmerina hardmaniana, a marine centric planktonic diatom in a coastal mangrove ecosystem- implication for coastal carbon cycling
Keywords:diatom, phytoplankton bloom, mangrove, carbon cycling
Large celled diatoms play an important role in export of carbon in coastal ecosystems. In the Sundarbans mangrove ecosystem located on the delta of Ganga-Brahmaputra-Meghna riverine systems and facing the coastal Bay of Bengal, a bloom of Palmerina hardmaniana (Greville) Hasle was tracked in 2015. The bloom of this centric diatom species was tracked from April- July, 2015 in Sundarbans Biological Observatory Time Series (SBOTS) site of Sundarbans. During pre-bloom (April) dissolved oxygen (DO) concentration was 6.82 mg/L while during bloom (May-June) DO concentration decreased to 3.83 mg/L. This also coincided with Chlorophyll-a concentration which ranged from 0.22-6.28 mg/L during the study period, with highest concentration of 6.28 mg/L in bloom period and overwhelmingly dominated by cells belonging to Palmerina hardmaniana (40.8 X 104 cells/L). In total 72 phytoplankton species were observed from April-July, 2015 in SBOTS site. The frustules of Palmerina hardmaniana ranged from 291-358 µm in length and from 195 to 260 µm in width. Based on rbcL phylogeny of RuBISCO, the dominance of P. hardmaniana was also confirmed. Increased air and surface water temperatures in SBOTS site showed significant correlation with observed cell abundance of P. hardmaniana with the onset of bloom. This is the first report of P. hardmaniana bloom in the coastal Sundarbans mangrove ecosystem. Therefore, understanding the physiological success of this centric diatom species in relation to dynamic environmental conditions has consequences for tracking export of carbon by centric diatoms in coastal water and resulting implications for coastal carbon cycling.