The heat and irradiation driven degradation of the diagnostic pigments in marine phytoplankton and the compositions of special degradation products.

Marine phytoplankton stands as one of the most crucial components of marine ecosystems, so tracking it using appropriate biomarkers holds significant meaning. Chlorins are a sort of degradation products derived from the diagnostic pigment of marine phytoplankton and serve as valuable biomarkers for describing the temporal and spatial distribution of phytoplankton. However, previous research has not qualitatively or quantitatively studied multiple Chlorins, nor has it clearly revealed the conditions of their formation. Thus, this study investigated the chemical structure and formation mechanism of Chlorins in Chlorophytes, Prochlorococcus, and Chrysophytes communities by experiencing specific heat and irradiation conditions. According to the standardized redundancy analysis results, Phytin-a and its analogues with shorter phytyl chain are sensitive to irradiation intensity, and different Phytin-a analogues represent different degradation pathway of Chl-a. The composition and concentration of Phide-a and its further degradation products emerged as the primary thermosensitive components, capable of indicating and reversing temperature fluctuations within the environment. During the degradation processes of Chl-a, the carotenoids of each phytoplankton can also affect the degradation direction of Chl-a. Phycourobilin can cause Chl-a in the Prochlorococcus group to transform into special Phide-a analogues relying on low irradiation intensity. Zeaxanthin and Diatoxanthin dominate the conversion of Chl-a in Chrysophytes, and tend to cause heat-driven degradation of pigments. Zeaxanthin and Prasinoxanthin can also mediate the degradation of Chl-a in Chlorophytes. Thus, Chlorophyll and the composition of its Chlorins briefly reveal the rates of degradation and light intensity, and the carotenoids and their Chlorins can represent the temperature condition in the environment. These results imply that Chlorins can be utilized as biomarkers to infer the distribution and abundance of phytoplankton communities, reflecting the environmental factors in which phytoplankton live.