Ecosystem Services of Seaweeds Abhijit Mitra Department of Marine Science, University of Calcutta, 35 B.C. Road, Kolkata 700019, India Seaweeds or benthic marine algae are the group of plants that thrive either in marine or brackish water environment. They are macroalgae and contain photosynthetic pigments. Like the terrestrial producer community, the seaweeds can prepare their own food with the help of sunlight and nutrient present in the seawater. Seaweeds are found in the coastal region between high tide to low tide and in the sub-tidal region up to a depth where 0.01 % photosynthetic light is available. They require hard substratum for their growth, which may be tree trunks (preferably mangroves) that get submerged during the high tide or even brick or boulders that are often laid to enter the island from the adjacent bays or estuaries (Fig. 1). Fig. 1. Seaweed (Ulva lactuca) on the brick path in the intertidal zone Plant pigments, light, exposure, depth, temperature, tides and the shore characteristic combine to create different environment that determine the distribution and variety among seaweeds. The important criteria used to distinguish the different algal groups based on the recent biochemical, physiological and electron microscopic studies are: a) photosynthetic pigments, b) storage food products, c) cell wall component, d) fine structure of the cell and e)