# Valuable Nutri from _Ulva rigida_: Modulation by Seasonal and Cultivation Factors
## 3 Results and Discussion
### Ash and Mineral Profile  
Throughout the year, ash content varied between 25.7 \(\pm\) 1.3% DW and 38.8 \(\pm\) 1.0% DW, reaching the maximum levels in June and the minimum in November (Figure 2A). These results were not directly comparable to those of the literature, as, to our knowledge, there is no reported information regarding seasonal variation of ash content specifically in _U. rigida_, even in wild samples. Nevertheless, recently, [PERSON] and coworkers [31] revealed slightly higher ash levels in summer (38% DW) comparatively to fall/winter (31% DW) seasons for _Ulwa_ spp. cultivated in a land-based intensive cultivation system (_p_ < 0.05). Still, the yearly average (33.5 \(\pm\) 3.5% DW) falls within the range of previously reported values for wild specimens of the same species collected in several countries (14\(-\)31% DW) [24; 35; 45]. Figure 2: Seasonal variation of (**A**) ash (% DW), (**B**) sodium and potassium, (**C**) calcium and (**D**) magnesium (mg/100 g DW) in _Ulwa rigida_ produced by IMTA under different conditions of flow rate, high (\(\odot\)) and low (\(\blacktriangle\)); and of stocking density, high (full lines) and low (dotted lines). Standard deviations are represented as bars (n = 3, in triplicate). Regarding the effect of cultivation conditions, stocking density was found to have a significant influence on the modulation of this nutrient, leading to increased ash levels when set to low. This tendency was also observed in a small study comparing the nutrient composition of _Uliva ohnoi_ cultivated under three different stocking densities [46]. Apart from this study, little information is available regarding the influence of this growing condition on the ash content of macroalgae. In opposition, variation of flow rate in IMTA conditions had no significant impact on the ash content of the analysed samples, although values tended to increase when this parameter was set at low. These observations agree with those of previous authors who have studied the effect of nitrogen availability in the composition of farmed _U. rigida_[47] and _U. lactuca_[12]. In their study, researchers hypothesized ash content to be controlled by nitrogen levels, in the presence of low concentrations of this nutrient [48]. This could also explain why ash levels varied inversely to those of protein throughout the present study. Indeed, the previous protein content reached its minimum and maximum in the summer and winter months, respectively, whereas, for ash levels, an opposite tendency was observed. Among macrominerals, sodium (Na) was predominant (3604 \(\pm\) 384 to 4700 \(\pm\) 290 mg/100 g DW), followed by magnesium (Mg, 2695 \(\pm\) 241 to 3992 \(\pm\) 196 mg/100 g DW), potassium (K, 2157 \(\pm\) 204 to 3460 \(\pm\) 336 mg/100 g DW) and calcium (Ca, 387 \(\pm\) 37 to 498 \(\pm\) 71 mg/100 g DW) (Figure 2B-D). Na and K levels were substantially higher than those established for wild _U. rigida_ (400-576 mg/100g DW and 817-1100 mg/100 g DW) [17; 49]. As previously described, there are seasonal, environmental and physiological factors causing variations in the mineral content of seaweeds, even among the same species [18; 50; 51; 52]. However, the disparity in sodium content could be related to the methodology used in sample preparation, as our samples were washed with freshwater from \"Lagoon of Aveiro\" (naturally salted), instead of distilled water. As a result, Na/K ratio varied between 1.2 \(\pm\) 0.1 and 1.7 \(\pm\) 0.3), which is higher than that determined by other authors for the same species (0.4-0.7) [17; 49]. Nevertheless, the obtained values were comparable to those reported in the literature for _U. lactuca_ (\(<\) 2.4) [53]. The benefits of consuming foods with a low Na/K ratio in the regulation of blood pressure are well documented [54]. In this sense, the introduction of macroalgae in Western diets could be an asset to improve or maintain cardiovascular health.