Physiological and growth responses of Eucheumatopsis isiformis morphotypes to different light and temperature regimes

Abstract In the Yucatán Peninsula, México, the red eucheumatoid algae Eucheumatopsis isiformis has been proposed as a candidate for mariculture to obtain carrageenan, a sulfated polysaccharide widely used as a food thickener and stabilizer. As a part of the efforts to develop tropical seaweed cultivation in the region, we studied the photophysiological and growth responses to different light and temperature levels of two morphotypes with contrasting forms and thicknesses, to determine the optimal levels for large‐scale cultivation. First, in laboratory experiments, we quantified changes in photosynthesis and respiration rates, pigment content, and growth rate under low‐, medium‐, and high‐light intensities. In a second approach, we scaled up these experiments in a mesocosm system using the optimal light levels identified to test the response to short‐term increases in temperature according to seasonal variation. This study showed how irradiance modulated all responses; pigmentation was reduced while photosynthetic capacity, saturation irradiance, and growth increased under high light in both morphs. The thinner morphology (M1) showed the highest photosynthetic capacity and a linear response to light (LL<ML<HL), standing as a better candidate for cultivation. Temperature experiments in M1 showed that light acclimation modulates photosynthesis responses; it was positively affected under low light, while at high light it was not. Hence, light conditions driven by seasonal changes play an important role in the performance of E. isiformis, and special attention should be focused on the vertical cultivation system, which can regulate the incident light to maximize outcomes. The improvement and development of E. isiformis cultures are feasible and could provide an alternative industry for local fishermen, but more information is needed, particularly related to temperature and nutrient availability.