Occurrence of cyanobacteria (Richelia intracellularis)-diatom (Rhizosolenia hebetata) consortium in the Palk Bay, southeast coast of India

Symbiotic association of heterocystous cyanobacterium, Richelia intracellularis Schmidt with oceanic centric diatom, Rhizosolenia hebetata is reported from the Palk Bay, southeast coast of India. One to six trichomes of R. intracellularis were occluded inside the periplasmic space of R.hebetata, with their prominent heterocyst pointing towards the valve of the host. Each of these trichomes had 14 to 23 vegetative cells caped by a terminal heterocyst enriched with the nitrogenase enzyme. Density of Rhizosolenia containing R. intracellularis ranged between 120 and 260 cells L-1, and present uniformly in the water column. R. intracellularis is a diazotroph, can contribute substantially to the N-2 budgets thereby, promoting a different food web in the Palk Bay.