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All macroscopic algae occurring in the marine habitat and coastal brackish waters are known as seaweeds. They from one of the important marine living resources and belong to four major classes namely Chlorophyceae (green algae), Phaeophyceae (brown algae), Rhodoyhyceae (red algae) and Cyanophyceae (blue-green algae). Seaweeds are the only source for the production of phytochemicals namely agar-agar, carrageenan and algin, which are extensively used in various industries such as food, confectionary, textiles, pharmaceuticals, dairy and paper industry mostly as gelling, stabilising and thickening agents. Seaweeds are also used as human food animal feed and manure in several countries.

Seaweed is a popular term used to collectively describe marine macroalgae. Among this large and diverse  assemblage of photosynthetic marine organisms are  a number of species with a varied array of uses; when  used for human consumption, they are more popularly  known as “sea-vegetables.” This collective of convenience includes the macroscopic, multicellular, red,  green, and brown algae. Seaweeds are often abundant and predominantly found in the near-shore  marine ecosystems in all the oceans of the world. As a result of their diverse intercellular compounds  including alginic acid, carrageenans, and agar, seaweeds  have very important industrial applications.

Being important primary producers in marine ecosystems, macroalgae are an integral component of near-shore environment and form a fundamental part of the basis of the photosynthetic food chains, playing a role similar to that of terrestrial plants. In these natural environments, seaweeds often perform a large number of ecosystem services (e.g., nurseries, nutrient cycling, and reduction of coastal erosion among others), which are neither fully costed nor often appreciated by the public or users of the marine environment. Humans have wild harvested (sometimes called “wild crafting”) and cultivated seaweeds for several centuries for animal and human consumption as well as other applications including valuable sources of phycocolloids and most recently, researched as feedstock for biofuels and carbon sequestration.

Like many other estuaries and coastal regions, Long Island Sound suffers from anthropogenic eutrophication. This phenomenon, the addition of nutrients to the system as a result of human activities, is a consequence of the human alteration of the nitrogen cycle on a global scale. In coastal waters and estuaries primary production by phytoplankton, seaweeds, and seagrasses is generally limited by the availability of dissolved inorganic nitrogen, present as nitrate, nitrite, and ammonium. The sources of the inorganic nitrogen added into coastal waters and estuaries are several: fertilizer run-off from residences, agriculture, septic seep into groundwater, fossil fuel combustion, and wastewater treatment plant discharges.

Seaweeds or marine macro algae are primitive non-flowering plants without true root, stem and leaves. They form one of the commercially important marine living renewable resources. They are the only source for the production of phytochemicals such as agar, carrageenan and algin. Seaweeds occur in the intertidal, shallow and deep waters of the sea upto 180m depth and also in estuaries and backwaters. They grow on rocks, dead corals, stones, pebbles, solid substrata and on other plants.