Elemental and Nutritional Characterisation with Vibrational Spectroscopy Analysis of _Ulva_ sp., _Gracilaria multipartite_, and _Sargassum multicum_  
[PERSON]  
1 MARE--Marine and Environmental Sciences Center/ARNET-Aquaute Research Network, ESTM, Polytechnique University of Leirita, Edificio Cetmares, Av. Porto de Pesca, 2520-641 Peniche, Portugal 1  
Chlorophyta (class Ulvophyceae), Rhodophyta, and Ochophyta (class Phaeophyceae), respectively [3; 4]. Seaweeds are well-known for their high nutritional value [5], the carbohydrate, protein, lipid, and ash content of which varies between approximately 33 and 75%, 10 and 15%, 1.5 and 4%, and 3 and 47% respectively, while the dry weight varies between 10 and 20% [5; 6]. However, their chemical composition can vary depending on the species, life cycle phase, geographical, area and environmental conditions [7], such as the concentration of dissolved gases (CO\({}_{2}\) and O\({}_{2}\)), light intensity, mineral content (salinity and nutrients), temperature, ultraviolet radiation, various pollutants, pathogenic agents (fungi, viruses, and bacteria) and herbivory [2]. In order to adapt to these environments, the cells of these organisms produce bioactive compounds that often have beneficial effects on human health [8; 9]. These organisms are therefore being studied for their abundance of compounds with diverse biological properties, including primary and secondary metabolites [10]. The high concentration of minerals in algae is also worth mentioning, including both macro nutrients, such as calcium (Ca), phosphorus (P), magnesium (Mg), sulphur (S), sodium (Na), chloride (Cl), and potassium (K), and micro minerals, including iron (Fe), zinc (Zn), copper (Cu), iodine (I), selenium (Se), manganese (Mn), chromium (Cr), molybdenum (Mo), fluorine (F), boron (B), cobalt (Co), silicon (Si), aluminium (Al), arsenic (Ar), tin (Sn), lithium (Li), and nickel (Ni) [11]. Seaweeds normally contain these elements in quantities between 15 and 25 per cent of their dry weight. Normally, the Na/K ratio is low, which has been shown to confer benefits to humans, such as reducing hypertension [12]. _Ulva_ spp. (Chlorophyta, Ulvophyceae, Ulvales, Ulvacae) is a cosmopolitan taxon [13], commonly known as sea lettuce, forming a frond or blade and a small disc that allows it to attach to the substrate (Figure 1) [14]. The genus is found in a wide variety of coastal environments, including tidal pools, intertidal rocks and reefs, brackish water, and even freshwater, where nutrient concentrations are high [15]. _Ulva_ spp. is a rich source of essential polysaccharides, including ulvans, and oligosaccharides, which can account for approximately 40 per cent of its dry weight (dw) [6]. _Gracilaria_ spp. (Rhodophyta, Florideophyceae, Gracilariales, Gracilariaceae) is one of the most valuable marine red algae in the world [16]. Nutritionally rich, the _Gracilaria_ genus contains proteins, vitamins, carotenoids (including beta-carotene, lutein, and zeaxanthin), pigments, dietary fibre, and omega-3 and omega-6 fatty acids [16; 17]. It is regarded as a source of agar, a phycocolloid used in the manufacture of consumer products, including food, pharmaceuticals, and cosmetics, among others [18; 19]. _Gracilaria multipartita_ ([PERSON] (Figure 1) is a European species that grows in high temperatures and light, with a high mineral content [20; 21]. This species has been underrepresented in the literature, with very little information available on its nutrient and mineral content, except for the species' agar content [22]. Figure 1: From left to right, _Ulva_ spp., _Gracilaria multipartita_, and _Sargassum muticum_, in January 2024, Portugal. Sargassum_ spp. (Ochrophyta, Phaeophyceaeae, Fucales, Sargassaceae) contains polysaccharides, proteins, polyphenols, lipids, sterols, carotenoids, and other bioactive compounds with therapeutic properties [23]. Studies have demonstrated that brown seaweeds possess protein values ranging from 5 to 15% of their dry weight, with an average ash content between 13 and 30% of the dw [24].