title: Dynamic sinking behaviour in marine phytoplankton: rapid changes in buoyancy may aid in nutrient uptake.
abstract: Phytoplankton sinking is an important property that can determine community composition in the photic zone and material loss to the deep ocean. To date, studies of diatom suspension have relied on bulk measurements with assumptions that bulk rates adequately capture the essential characteristics of diatom sinking. However, recent work has illustrated that individual diatom sinking rates vary considerably from the mean bulk rate. In this study, we apply high-resolution optical techniques, individual-based observations of diatom sinking and a recently developed method of flow visualization around freely sinking cells. The results show that in both field samples and laboratory cultures, some large species of centric diatoms are capable of a novel behaviour, whereby cells undergo bursts of rapid sinking that alternate with near-zero sinking rates on the timescales of seconds. We also demonstrate that this behaviour is under direct metabolic control of the cell. We discuss these results in the context of implications for nutrient flux to the cell surface. While nutrient flux in large diatoms increases during fast sinking, current mass transport models cannot incorporate the unsteady sinking behaviour observed in this study. However, large diatoms appear capable of benefiting from the enhanced nutrient flux to their surface during rapid sinking even during brief intervening periods of near-zero sinking rates.
authors.affiliation: Deparment of Integrative Biology, University of South Florida, Tampa, FL 33620, USA Marine Science Department, University of Texas at Austin, Port Aransas, TX 78373, USA bgemmell@usf.edu.
authors.forename: Brad J
authors.identifier: 0000-0001-9031-6591
authors.initials: BJ
authors.lastname: Gemmell
authors.affiliation: Marine Science Department, University of Texas at Austin, Port Aransas, TX 78373, USA.
authors.forename: Genesok
authors.initials: G
authors.lastname: Oh
authors.affiliation: Marine Science Department, University of Texas at Austin, Port Aransas, TX 78373, USA.
authors.forename: Edward J
authors.initials: EJ
authors.lastname: Buskey
authors.affiliation: Marine Science Department, University of Texas at Austin, Port Aransas, TX 78373, USA.
authors.forename: Tracy A
authors.identifier: 0000-0002-5717-8163
authors.initials: TA
authors.lastname: Villareal
mesh_terms: D017377:Diatoms; D020387:Food Chain; D009792:Oceans and Seas; D010839:Phytoplankton; D012623:Seawater; D014872:Water Movements
keywords: diatom; nutrient flux; phytoplankton; sinking