Short-term thermal exposure effects on growth rate, photosynthetic performance, and chemical composition in Pyropia spiralis (Rhodophyta) from the brazilian coast: insights and limitations

Red macroalga Pyropia spiralis thrives in the upper intertidal zone and demonstrates remarkable resilience to environmental fluctuations, attributed to protective mechanisms against factors like solar radiation, temperature, and desiccation. The aim of this is study was assess the thermosensitivity and tolerance of P. spiralis, subjecting to five temperatures (15, 20, 25, 30, and 35 °C) evaluating growth rate, photosynthetic performance, and chemical composition. The hypothesis states that higher temperatures will reduce growth and photosynthesis, overstimulate metabolism, degrade pigment composition, and trigger the synthesis of protective metabolites for stabilizing cellular structures under elevated temperature conditions. The study revealed thermotolerance between 15 and 25 °C, characterized by stable energy dissipation and minimal pigment changes. Yet, at 30 and 35 °C, there was significant thermosensitivity, leading to a notable drop in photosynthesis and pigments. Carbon-to-nitrogen (C:N) ratio, notably below 20 (9.58 at 15 °C and 7.86 at 25 °C), indicated a balanced growth characterized by optimal proportions of minerals, carbohydrates, and proteins. P. spiralis ' nutritional traits make it a promising candidate for use in seaweed-based products. Analysis of specific amino acids highlighted an upward trend at 25 °C, while higher temperatures induced a thermal-response profile associated with osmoprotectants, primary stress signals, and glutathione biosynthesis. Additionally, lower temperatures were linked to increased soluble carbohydrates, whereas higher temperatures inversely impacted protein accumulation. It is crucial to note that, being just one variable, the study provides a partial perspective, highlighting the importance of future, multifactorial analyses.