Photosynthetic pigments in surface sediments in the northwest of the Bohai Sea, China: Potential implications for sediment deposition of brown tides of Aureococcus anophagefferens in coastal waters

Abstract It is not clear whether brown tide, caused by pico-pelagophyte, can lead to significant settlement of organic matter and potentially induce environmental degradation, such as hypoxia. In this study, surface sediment pigment compositions were studied after the brown tide bloom in the northwestern Bohai Sea (NWBS), China, to confirm whether organic matter from the brown tide can deposited to sediment. Seventeen kinds of photosynthetic pigments were detected in the sediments, and chlorophyll a was the most dominant pigment. Fucoxanthin and β,β-carotene were the main carotenoids. Especially abundant 19′-Butanoyloxy-fucoxanthin (But-Fuco), the characteristic indicator of brown tide Aureococcus anophagefferens , was universally detected in the sediments, with the average proportion of But-Fuco among a total of 13 carotenoids reaching about 9.2%. The horizontal distribution of these dominant pigments followed similar patterns and high levels were observed in the middle of the study areas, while the higher ratio value of But-Fuco/Fuco appeared in A. anophagefferens bloom area. Significant correlations were found between Fuco and But-Fuco, Diato and But-Fuco, and Diadino and But-Fuco, while almost no correlations were observed between pigments and total organic carbon (TOC) or sediment grain size. The universal observation of But-Fuco and its high content in A. anophagefferens bloom areas confirmed that brown tide could induce additional abundant deposition of organic matter to sediment. Our results support the view that the contribution of pico-plankton to carbon export from the ocean surface cannot simply be ignored, and indicate the fundamental influence of brown tide on the sediment environment for the first time.