Award: OCE-1155663

The project goal was to combine existing methods for silica production using a radioisotope with measures of silicon deposition rates using the fluorescent probe to gain further understanding into the role that individual diatom groups play in the assemblage processes. This project included laboratory and field work, along with student training and public outreach. Laboratory work was conducted using diatom clones isolated cells from the north central California Coast. These experiments helped refine the incorporation ratio of fluorescent dye relative to diatom silica among the clones. Comparing our data with previous work helped produce the most robust analysis of incorporation ratio to date and provided the essential information for making the fluorescent dye a quantitative field method. The methods resulting from this laboratory work were tested in the field. This project supported one field cruise and work on two cruises of opportunity. The 2013 DYE labeling of diATOM silica (DYEatom) took place aboard the R/V Pt. Sur in June/July. The goal was to sample a variety of diatom assemblages in various states of nutrient stress (i.e. replete to chronically stressed), and this was achieved. The Ph.D. student supported and trained by this project was able to conduct additional work aboard two cruises of opportunity: June 2014 aboard the R/V Melville and April 2015 aboard the R/V Oceanus. The refined field method resulting from the laboratory and cruise work was published in 2015 (Limnology and Oceanography: Methods). Perhaps the most exciting results are determination of kinetic parameters for individual diatom groups in the field. During the 2013 DYEatom cruise, Chaetoceros and Pseudo-nitzschia routinely switched as the most abundant diatom group, but this new method showed their efficiency for taking up silicon from seawater was significantly different. This experiment provides the first direct evidence that Pseudo-nitzschia has a high capacity for persistence at low silicic acid, this would be due to their high affinity for Si at low substrate. This result is consistent with explanations for the dominance of this organism group in waters affected by anthropogenic activity, e.g. increases in N and reductions in Si which has been coincident with shifts away from large diatoms dominating the phytoplankton to Pseudo-nitzschia and dinoflagellate dominance. This project also supported multiple outreach efforts by the PI at his home institution, Dauphin Island Sea Lab. The phytoplankton 3-d models developed for outreach have also been used numerous times by the PI and his group at DISL?s Annual open house, presentations to students either during their field trips to DISL or to local classrooms in the city of Mobile, AL (Figure 7). In addition to DISL-based instruction, to date, the models have been used in teachers? workshops at Florida Polytechnic, for museum displays in the Canadian Museum of Nature – Musée Canadien de la Nature Ottawa, and used by colleagues in Europe to scale up fluid dynamic studies of phytoplankton and shear; these represent only those parties who have used the models and communicated it. Additionally, a DISL Educator has used the models and recently presented at the 2017 National Marine Educators Association meeting in Charleston, South Carolina. This outreach drew much acclaim from educators with mid-Atlantic Sea Grant programs to classroom educators at multiple levels. The two teaching-aid posters produced have been freely given to regional teachers for use in their classrooms in addition to using in DISL Discovery Hall Program?s Plankton module instructional unit, which is presented to several hundred primary school children annually. Last Modified: 07/05/2017 Submitted by: Jeffrey W Krause