# Different _Chondrus crispus_ Aquaculture Methods and Carrageenanan Extraction
## 4 Discussion

Table 5: Weekly mean SGR in percentage of growth (with standard deviation) compared with the mean percentage of total nutrient reduction (with standard deviation). Values marked with the color green are the highest values, and red are the lowest. 1.31%/day, after the first 14 days of testing [55]. Most of the tested methods surpassed this value in their first week of growth, with the exception of Nursery 3 in Tordos and the Cage method (Table 2). It is not possible to make a direct comparison with Nursery 2, because this method only had weight results at the end of the trial. The results obtained indicate that, according to the overall SGR, the most effective growth methods are free floating, where the algae are loose and stirred by aeration only. However, these methods have only been tested on a small scale, so another large-scale test would be needed to be sure of the effectiveness and suitability of this method of algae production in an industrial environment [56]. Biomass harvesting is also problematic in this methodology. The data collected from previous experiments with _C. crispus_[55] allowed us to establish a profile and increase rates of growth for this species. This work allowed us to replicate those results and take a step forward in establishing a suitable farming method for _C. crispus_ biomass on an industrial scale in a temperate climate. _Chondrus crispus_ is a species, as demonstrated by this and previous works, that has slow initial development (SGR = 1.31%), but whose growth rate increases greatly later (SGR = 4.23) in the farming process. As suggested by [PERSON] in 2001, in order to start the cultivation there is a need for low initial seaweed densities to be exposed to various controlled factors (such as temperature and nutrient availability) [57]. This idea was implemented in the study and resulted in the SGRs achieved. The data indicate that this should be considered when designing a farming strategy and, as such, further development is needed in order to optimize SGR values in large open tanks. The analysis of carrageenan yield is very important for the study, due to being the most important economic compound in _C. crispus_. There is a possibility that growth in a controlled situation may not be favorable for carrageenanan production. Thus, the type of cultivation may impact the polysaccharide yield, as demonstrated by [PERSON] et al. [58] and [PERSON] et al. [59], who demonstrated that the seaweed specie can change their polymer production due to the cultivation methods and this is not linear between species (using the same cultivation methods). As for carrageenanan content, there was a notable difference between the optimized aquaculture method tested in carrageenanan yield and the wild specimen production. This carrageenanan production is in line with the literature, considering that wild seaweed presented higher carrageenanan levels than reported in previous works [60; 61; 62]. Wild seaweed may have higher carrageenanan content because there is an accumulation of carrageenan and overproduction as a response to stress, either by physical stress (being an intertidal species, constantly pushed and pulled by the tide) or chemical (nutrient scarcity). The polysaccharide production may be a survival technique, storing energy in the compound. This is a known survival strategy in algae, which can produce different compounds as a stress response [63; 64]. In the aquaculture experiment there was no such stress, with a high nutrient concentration in the water and no tide to induce stress in the algae, therefore there was no increased need for the specimens to produce carrageenanan. This indicates that it is necessary to optimize these methods in order to mitigate the carrageenanan decrease in aquaculture algae. Regarding the reduction in nutrients by the algae, it is possible to interpret that the nutrient concentration influences the growth of the algae in a positive correlation. It might be interesting to repeat this kind of study with a greater focus on nutrient consumption and bioremediation.