Seaweed (known as marine algae) has a tradition of being part of the animal feed in the coastal areas, from ancient times. Seaweeds, are mixed with animal feed, because when consumed alone can have negative impact on animals. Thus, seaweeds are very rich in useful metabolites (pigments, carotenoids, phlorotannins, polyunsaturated fatty acids, agar, alginate and carrageenan) and minerals (iodine, zinc, sodium, calcium, manganese, iron, selenium), being considered as a natural source of additives that can substitute the antibiotic usage in various animals. In this review, we describe the nutritional values of seaweeds and the seaweed effects in the seaweed-based animal feed/supplements.

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Oceans and seas form a large body of water that contains a natural biodiversity. For humans, represents a resource, which makes this a point of interest, from researches to improve the economy. Seaweeds produce many compounds and secondary metabolites that can be used in different fields of industry such as food, agricultural, pharmaceutical and health. Even though seaweeds are ancestral resources, recently it was notorious a global interest in knowing more about its potentials, where biotechnology plays an important role in research. Studies showed that seaweed has many bioactive compounds beneficial to plant development, giving them a great potential as an agricultural fertilizer. Adding seaweeds to the soil provides organic matter, minerals, trace elements, growth plant regulator, metabolites, vitamins, and amino acids and it can work as a soil conditioner. In Portugal, the use of seaweeds for agriculture is important since long time ago. In the past, populations that lived near coastal zone depended on the seaweeds as a family subsistence but, throughout the years, synthetic fertilizers replaced seaweeds. Our work aimed to assess the potential of the extracts obtained from Ascophyllum nodosum and from Sargassum muticum as an agricultural fertilizer. This evaluation was carried out with rice plants (Oryza sativa) and lettuce (Lactuca sativa), in germination bioassays, the culture of rice and lettuce plants in pots, and culture of lettuce plants in hydroponics. For that, seaweed liquid extracts were used in different concentrations in different bioassays. Results show that extracts obtained from two seaweeds, A. nodosum and S. muticum, can be promissory plant biofertilizer at a concentration of 25% and had a positive effect on seed germination, plant development, and production.

Marine macroalgae are a vast source of raw materials and biologically active molecules used in the pharmaceutical, cosmetic, food and agricultural industries. The search for a food free of chemical residues by consumers has led producers to use environmentally friendly and economically viable products as they are a source of natural compounds, forming a new and promising area of study. In this context, concentrated marine algae extracts (CMAEs) are an important alternative in this production model. This work aimed to evaluate the effects of CMAEs as biostimulants in plant metabolism, promotion of growth, development and production of pepper (Capsicum annuum L.) cultivated in a greenhouse. This work was carried out from 24 June to 30 October 2019. The number of leaves, plant length, fresh and dry plant mass, root length, root fresh and dry mass, fruit production and the metabolic performance were evaluated. The results of the stomatal conductance of pepper plants, production and biofortification were related with the levels of nutrients absorbed by the plant, which reflected the effect of the applied biostimulant. The dose that showed the most promising results was the 0.5% concentration of CMAEs.

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