Optimization of seedling production using vegetative gametophytes of Alaria esculenta

Alaria esculenta is a brown seaweed with a great potential for biomass production due to its high productivity and high content of carbohydrates, proteins, vitamins, minerals and bioactive compounds like phlorotannins and pigments. Alaria cultivation is performed either by collection and settlement of zoospores on ropes to develop seedlings, or by production of the seedlings from vegetative gametophyte cultures. Contrary to the zoospore technique, the use of gametophyte cultures has the potential to provide a constant, year-round supply of seedlings. There is a need for optimizing the production methods such as the maintenance of the gametophyte cultures, gametogenesis, seeding process and deployment time. The purpose of this dissertation is to optimize several parameters involved in Alaria cultivation using vegetative gametophytes and provide qualitative and quantitative information related to kelp phlorotannins. Optical density and in vivo fluorescence were evaluated as an alternative method to estimate gametophyte biomass. Both methods showed linearity with the dry weight. The cultures were also supplemented with a possible growth enhancer and the effect evaluated on the cultures, however no growth improvements were noticed on these cultures. When the seedlings production is initiated, the fertility of vegetative gametophytes needs to be switched on. The fertility induction was evaluated with three different photoperiod regimes under white light, where the best performance was accomplished by 23 hours light over 8 days. The seeding density is the next step to optimize seaweed industry. Higher and lower densities bring several disadvantages to the development of the sporophytes. Thus, four densities of fertile gametophyte cultures were tested, where a density per dry weight of 0.8 mg/mL produced the most acceptable number of sporophytes on the twines. For the estimation of sporophyte growth, manual measurements, such as sporophytes counting and length measurement, are extremely time-consuming methods. An alternative method based on image analysis was tested to estimate the percentage of growth of the seedlings and compared with the manual method. The image analysis method was shown to have a good relationship with the sporophyte measurements, bringing a faster and easier way to estimate the seedlings growth. A. esculenta and S. latissima could represent a viable source of phlorotannins (PHL) due to the fast and efficient grow of these species. The juvenile stages of these species had an average of 4.11 and 3.08 mg PHL/g algae, respectively. It was also observed that the phlorotannin content in the Alaria gametophytes increased during fertilization. Two forms of phloroglucinol were documented in both species but due to the lack of studies related with the phlorotannin characterization of these species no more compounds were identified.