The demand for carrageenan, a sulfated polysaccharide obtained from Eucheumatoids species (Kappaphycus / Eucheuma ) widely used as a food thickener, has increased in recent years. Efforts to cultivate these carrageenan-producing species in the Americas have been successful in Brazil and some Caribbean islands with the introduced species K. alvarezii (Hayashi et al., 2017). In Mexico, Eucheumatopsis
isiformis ( formerly Eucheuma isiforme) a native species found in the southern Gulf of Mexico and the Caribbean produces a high-quality iota carrageenan suitable to be considered a viable source of carrageenan with yields up to 40% of its dry weight (Freile-Pelegrín and Robledo, 2006). Under the support of the MARINER ARPA-e DoE program, the "Tropical S eaweed F arm" project aims to design and develop a cultivation system for large-scale production of this tropical seaweed. To achieve this, it is necessary to select and domesticate cultivars of E. isiformis and basic physiological knowledge is crucial to understand the conditions for maximum growth and biomass production. In this study, morphotypes of E. isiformis were collected from a subtidal population in Yucatan (Dzilam de Bravo) and acclimatized to laboratory conditions (23°C + 80 µmol quanta m-2 s-1). Physiological responses (photosynthesis and growth) were determined at different light intensities: low, LL (80 µmol quanta m-2 s-1); medium, ML (250 µmol quanta m-2 s-1) and high, HL (550 µmol quanta m-2 s-1 ). Preliminary results have shown that one to two weeks are sufficient to acclimate the photosynthetic apparatus to each of the light conditions and that light levels had a strong effect on the photosynthetic parameters analyzed (maximum photosynthesis, respiration rates and saturation irradiance). Specimens under ML and HL showed thallus elongation and development of numerous lateral branches. The results suggest that E. isiformis
is able to tolerate higher irradiances under cultivation conditions, up to twice its photosynthetic saturation irradiance (Ek), without nutrient limitation. Preliminary chemical analyses of E. isiformis morphs revealed differences, including carrageenan content, so understanding the factors controlling their changes should be a priority. Further experiments are underway to extend these cultivars to outdoor conditions.