Benthic macro-algae, which are also termed as seaweeds are plentiful at sundarbans. These grow on any suitable substrata like roots and neumatophores of mangrove plants, walls of dykes, piers and pillars of jetties, edges and floors of mud pools, where water is trapped during low tide and on the body of the ropes and anchoring poles used by fishermen or women to tie their nets. They are extremely important from ecological point of view, as they are one of the important primary producers of the marine and estuarine environment of Sundarbans. Many gastropods (snails) and fishes graze on these benthic seaweeds. These seaweeds also get decomposed by bacteria and supply food to benthic clams, worms and other detritivores, which are preyed upon by crabs, brittlestars, and small carnivorous fishes and cephalopods (squids, cuttlefishes and octopus), all of which, in turn, are eaten by bottom dwelling predatory fishes like groupers.
Apart from that these macro-algae have tremendous biotech value and cultured world over. They are the source of agar- agar, which is used in bio-medical and microbiological research and industries and materials like carrageenan etc., which are used in confectionary industry. Due to their rich mineral content they are also utilized world over as mineral supplement, fodder and manure.
The benthic macro algae we found in Sundarbans are Enteromorpha intestinalis, E. prolifera, Ulva lacuta, Rhizoclonium grande (Chlorophyceae) and Catenella nipae, C. adnata, C. leprieurii, Gracilaria verrucosa, Bostrychea sp., Calloglossa sp.(Rhodophyceae).