Effect of Temperature on the Release of Transparent Exopolymer Particles (TEP) and Aggregation by Marine Diatoms ( Thala
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Effect of Temperature on the Release of Transparent Exopolymer Particles (TEP) and Aggregation by Marine Diatoms (Thalassiosira weissflogii and Skeletonema marinoi) CHEN Jie1), 2), GUO Kangli1), *, Daniel C. O. Thornton2), and WU Yi1) 1) Fourth Institute of Oceanography, Ministry of Natural Resources, Beihai 536007, China 2) Department of Oceanography, Texas A & M University, College Station, Texas 77843, USA (Received March 9, 2020; revised April 26, 2020; accepted August 20, 2020) © Ocean University of China, Science Press and Springer-Verlag GmbH Germany 2021 Abstract The presence of diatoms is accompanied by the production of a large amount of extracellular polymeric substances, which are mainly composed of carbohydrates. Transparent exopolymer particles (TEP) are a large class of extracellular polymeric substances with high stickiness that promotes the formation of aggregates and marine snow, which affects marine bio-carbon pump efficiency. The purpose of this research was to determine how temperature increases affect the allocation of cellular carbohydrates and the formation and aggregation of TEP. The results showed that the responses of two different diatom species (Thalassiosira weissflogii and Skeletonema marinoi) differed according to temperature. The cell density and chlorophyll a concentration of the former were not significantly correlated with temperature, while those of the latter were significantly decreased with increasing temperature. This indicates that the two species of diatom may have different heat tolerance ranges. A temperature increase will promote significant formation of TEP by both types of diatoms, including aggregation of S. marinoi as the temperature rises, meaning that the high temperature will produce an aggregate with a larger particle size and thus may increase the sedimentation rate of organic carbon. Moreover, the TEP aggregation of T. weissflogii did not increase; therefore, its particle size was smaller, and so it may remain on the sea surface at high temperatures for longer periods. These influences have a profound impact on the biogeochemical cycling of carbon. Key words
transparent exopolymer particles; diatom; Thalassiosira weissflogii; Skeletonema marinoi; aggregation
1 Introduction Diatoms in the ocean play an important ecological role, not only because of their high productivity but also because they can excrete large amounts of extracellular polymeric substances (EPS) (Hoagland et al., 1993; Thornton, 2002; Underwood and Paterson, 2003). EPS constitute 10% of the carbon in the oceanic dissolved organic carbon (DOC) pool (Chin et al., 1998; Verdugo et al., 2004). Most EPS are acidic polysaccharides, which can coagulate into transparent exopolymer particles (TEP) (Alldredge et al., 1993; Passow, 2002a). TEP are sticky, gel-like particles (Alldredge et al., 1993; Engel, 2000; Passow, 2002b) that affect the formation of aggregates, as they collide with diatoms and other particulate organic carbon (POC) to form larger particles that sink rapidly in the water column (Kiø
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