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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.

Seaweeds have been used as supplementary feed for livestock in Norway for centuries. Research activities on the use of seaweed as feed started early last century and continued until the late 1960s. The results were elusive, partly because the design of the experiments were imperfect. However, a long term experiment in the 1960’s demonstrated 6% higher milk production by cows supplemented mineral fortified Ascophyllum nodosum meal than in cows offered standard mineral supplement. The authors suggested that seaweed compounds might have had benficial effect on the rumen microflora. Seaweeds are a rich source of Se and antioxidants such as substituted phenols, polyphenols, vitamins, and vitamin precursors. Results from research last 10-20 years suggests that dietary supplementation with A. nodosum meal has positive effects on ruminant product quality and stress tolerance. Alginates have been documented to be non-specific immunostimulants. A. nodosum is currently commersially harvested and processed and sold as a feed supplement. Winter fed sheep and cattle in Norway needs to be given extra fat soluble vitamins and minerals, particularly vitamin E and Se, in order to ensure good animal health and production. Based on the aquired knowledge from international reseach on A. nodosum and its possible beneficial health effect, we tested if A. nodosum has immunestimulating effect and can be used as a substitute for synthetic vitamin E in sheep and cattle. Our hypothesis were that supplementing the diet with seaweed to sheep and lactating dairy cows would produce better adaptive immune response following immunization compared to no supplementation and similar to animals given extra vitamin E. Two feeding experiments were conducted, one continous with 40 pregnant ewes and one with 24 lactating dairy cows in a replicated Latin square design. The four supplement treatments applied were: A. Nodosum meal (SW), Natural vitamin E, Synthetic vitamin E, or Control. The average daily rate of A. Nodosum meal per ewe and cow in SW was 80 and 200 g DM, respectively. The ewes and their newborn lambs were monitored the entire indoor feeding period, from mating until pasture let out (200 d). In the ewes, supplementation with SW had no health effects compared to the other treatments, and serum IgG concentrations were reduced in the SW group.The adaptive immunity of the lambs was not affected by supplementation, and seaweed reduced the counts of different intestinal bacterial groups. However, seaweed interferred with the lambs passive immunity resulting in a mortality rate of 35 %, compared with 10% in Control. All cows responded well to immunization, but there were no significant effects of the diet on the immune response measured. The immunesupression observed in newborn lambs from ewes offered SW was likely du to impaired Ig absorption from colostrum, and we conclude that ruminants should not be supplemented with seaweed during peripartum. More research is needed on the identification of bioactive components in seaweed, their effects in animal health, the mechanisms related to their effects on the animal health and testing before seaweed should be used as a feed supplement to ruminants.

Seaweed aquaculture technologies have developed dramatically over the past 70 years mostly in Asia and more recently in Americas and Europe. However, there are still many challenges to overcome with respect to the science and to social acceptability. The challenges include the development of strains with thermo-tolerance, disease resistance, fast growth, high concentration of desired molecules, the reduction of fouling organisms and the development of more robust and cost efficient farm systems that can withstand storm events in offshore environments. It is also important to note that seaweed aquaculture provides ecosystem services, which improve conditions of the coastal waters for the benefit of other living organisms and the environment. The ecosystem services role of seaweed aquaculture and its economic value will also be quantitatively estimated in this review. 

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.