## 3 Results and Discussion
### Nutritional Analysis
Thus, all of the samples from Buarcos had very high Na content. Environmental conditions, such as temperature and salinity, may be a contributing factor, as algae tend to absorb more Na from water with higher salinity [65]. The highest concentrations of Ca were observed in _S. muticum_ (21.22 \(\pm\) 1.48 mg/g dw), while the lowest levels were detected in _Ulva_ sp. (8.99 mg/g dw). The Mg values were higher in the San Marcos species, which exhibit a concentration of 17.21 \(\pm\) 0.86 mg/g dw, and in _Ulva_ sp. (15.47 \(\pm\) 0.96 mg/g dw). The lowest Mg value obtained was found in the _G. multipartita_ from Buarcos (7.89 \(\pm\) 0.21 mg/g dw). Furthermore, P was the least representative of the macronutrients, with values ranging from 1.07 \(\pm\) 0.02 to 2.17 mg/g dw in _S. muticum_ from Buarcos to 2.17 \(\pm\) 0.07 mg/g dw observed in _G. multipartita_. Ca and P, the two main minerals in the human body, along with Mg, Na, and K, make up a significant proportion of the chemical constituents of algae [62; 65]. Regarding Ca and P, our results align with those reported by [PERSON] et al. [63] and [PERSON] et al. [64]. Among the Buarcos species, the highest Mg values were found to be lower in the green and brown algae compared to the red macroalgae [66], as observed by [PERSON] et al. [37]. Seaweeds are rich in these minerals, making them valuable food sources of essential nutrients. There is strong evidence that Ca from seaweeds enhances bone density, muscle strength, and nerve function [67; 68]. Brown macroalgae are also an excellent source of Mg, as noted by [PERSON] et al. [69]. Mg is crucial for numerous biochemical reactions in the human body, including energy production and muscle function [69], while P is essential for DNA and RNA formation, energy production, and bone health in humans. In seaweeds, P is necessary for energy transfer and storage [70]. In this study, Fe, Zn, Mn, and Cu were the most important trace elements in the four types of macroalgae analysed. The levels of Fe and Zn varied significantly between sites for _S. muticum_ but were within the values reported in the literature [63]. Fe was the most common trace element, with the highest levels found in the three Buarcos species, ranging from 221.21 to 279.52 ug/g dw. The lowest levels of Fe were found in the brown seaweed from San Marcos, with 116.30 ug/g dw. Fe is essential for the functioning of numerous proteins, including enzymes and haemoglobins in blood cells, and it is indispensable for the binding and transportation of oxygen through the tissues [71; 72]. As for Zn and Mn, the highest levels were found in the species from Buarcos beach, with Zn ranging from 8.37 to 28.90 \(\upmu\)g/g dw and Mn from 1.04 to 71.06 \(\upmu\)g/g. _S. maticum_ from Buarcos had the highest levels of Zn and Mn, which were significantly higher than those of the other samples. Lastly, _G. multipartita_ had the highest level of Cu (22.8 \(\upmu\)g/g dw), while the brown algae from San Marcos had the lowest (17.86 \(\upmu\)g/g dw). The Cu levels in our study were higher than those reported by [PERSON] et al. [63] and [PERSON] et al. [64]. High levels of Cu in seaweeds can indicate pollution in marine environments, as seaweeds can accumulate heavy metals from their surroundings [73]. However, Cu levels are below the maximum concentration allowed for human consumption in the European Union, which has set a maximum limit of 1 mg/day dry weight in seaweed [56]. The mineral content of seawater is therefore crucial to the growth and nutritional value of seaweeds, as it directly influences the accumulation of essential minerals in seaweed biomass, making it a rich source of nutrients for various applications [74].