Sargassum stenophyllum (Fucales, Ochrophyta) responses to temperature short-term exposure: photosynthesis and chemical composition

Sargassum species form extensive benthic beds in tropical and subtropical low intertidal and subtidal zones, acting as important drivers for marine community structure. Temperature, as one of the most important abiotic factor, affects seaweed performance and triggers changes in metabolic responses; therefore, laboratory experiments involving temperature ranges are tools for understanding seaweed engineering. The aim of this study was to assess the physiological vulnerability and sensitivity of Sargassum stenophyllum C. Martius exposed to five different temperatures by analyzing photosynthetic performance and chemical composition related to carbon and nitrogen metabolism. There were no significant differences in energy quenching between treatments, except at 35 °C, which showed decreased photochemical quenching and increased non-regulated non-photochemical quenching. Chlorophyll a and chlorophyll c at 15 °C and 35 °C exhibited lower amounts at the end of experiment. Protein content showed progressive diminution in the treatments. Total soluble carbohydrates content showed higher concentration as temperature increased. After 7 days, total amino acid content showed increase from 15 °C to 30 °C. No generalization between the amino acid patterns, although glutamine and glutamate content at 15 °C and 35 °C were reduced; and the highest values of isoleucine and leucine were detected at 35 °C. We postulated that accumulation of certain chemical compounds in S. stenophyllum results from a reallocation of carbon and nitrogen, osmoregulation responses and protection against oxidative stress. Results suggest this species’ tolerance ranges between 15 °C and 30 °C and sensitivity at 35 °C.