Dataset Information

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.

SUBMITTER: Gemmell BJ

PROVIDER: S-EPMC5069504 | biostudies-literature | 2016 Oct

REPOSITORIES: biostudies-literature

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Dynamic sinking behaviour in marine phytoplankton: rapid changes in buoyancy may aid in nutrient uptake.

Gemmell Brad J BJ Oh Genesok G Buskey Edward J EJ Villareal Tracy A TA

Proceedings. Biological sciences 20161001 1840

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, individ ...[more]

PMID: 27708154

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Project description:Children accrue experiences with buoyancy on a daily basis, yet research paints a mixed picture of children's buoyancy knowledge. Whereas children's predictions and explanations of the floating and the sinking of common objects are often based on a single feature (e.g., mass or facts), children's predictions of novel cubes reveal solution strategies based on mass and volume integrations. Correspondingly, category learning theory suggests that categories (e.g., floaters vs. sinkers) are easier to identify when items mainly vary from one another in the relevant defining features. For example, a set of cubes only varies in mass and volume and hence density, thereby being able to highlight the deterministic role of density when placed in water. Here we asked how item variation during hands-on exploration affects children's subsequent predictions and explanations of buoyancy. Kindergarteners and first-, second-, and third-grade children individually explored either a set of 10 systematically varied cubes (i.e., systematic condition; n = 95) or a set of 10 common objects (i.e., non-systematic condition; n = 96) in a water basin. Next, the children predicted the buoyancy of five new cubes and five new common objects one at a time. Subsequently, the children explained their predictions one subset at a time. The children in the systematic condition were more accurate in their predictions of the test cubes than the children in the non-systematic condition. Latent class regression analyses identified three cube prediction solution strategies. The children in the systematic condition were more likely to use a strategy in which buoyancy decisions were made based on an accurate integration of mass and volume, while the children in the non-systematic condition were more likely to use a strategy in which mass was given more predictive load than volume. A third strategy was characterized by guessing. Latent class analyses of the children's explanations revealed different explanation strategies, each appealing to several features, but as hypothesized, no clear condition differences were found. The findings indicate that even 5 min of exploration with systematically varied cubes can already help children use an advanced buoyancy prediction strategy. This provides evidence in favor of using category learning theory to inform early science education design.

Project description:Diatoms are marine primary producers that sink in part due to the density of their silica frustules. Sinking of these phytoplankters is crucial for both the biological pump that sequesters carbon to the deep ocean and for the life strategy of the organism. Sinking rates have been previously measured through settling columns, or with fluorimeters or video microscopy arranged perpendicularly to the direction of sinking. These side-view techniques require large volumes of culture, specialized equipment and are difficult to scale up to multiple simultaneous measures for screening. We established a method for parallel, large scale analysis of multiple phytoplankton sinking rates through top-view monitoring of chlorophyll a fluorescence in microtitre well plates. We verified the method through experimental analysis of known factors that influence sinking rates, including exponential versus stationary growth phase in species of different cell sizes; Thalassiosira pseudonana CCMP1335, chain-forming Skeletonema marinoi RO5A and Coscinodiscus radiatus CCMP312. We fit decay curves to an algebraic transform of the decrease in fluorescence signal as cells sank away from the fluorometer detector, and then used minimal mechanistic assumptions to extract a sinking rate (m d-1) using an RStudio script, SinkWORX. We thereby detected significant differences in sinking rates as larger diatom cells sank faster than smaller cells, and cultures in stationary phase sank faster than those in exponential phase. Our sinking rate estimates accord well with literature values from previously established methods. This well plate-based method can operate as a high throughput integrative phenotypic screen for factors that influence sinking rates including macromolecular allocations, nutrient availability or uptake rates, chain-length or cell size, degree of silification and progression through growth stages. Alternately the approach can be used to phenomically screen libraries of mutants.

Dataset Information

Dynamic sinking behaviour in marine phytoplankton: rapid changes in buoyancy may aid in nutrient uptake.

Publications

Dynamic sinking behaviour in marine phytoplankton: rapid changes in buoyancy may aid in nutrient uptake.

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