Award: OCE-1136477

This research examined functional, genetic and taxonomic diversity of eukaryotic phytoplankton in the surface ocean. Marine phytoplankton account for about half the annual global primary production. As the basis of the marine food web, phytoplankton are a crucial element in the biological pump whereby CO2 from the atmosphere is eventually sequestered in the deep ocean. Many factors contribute to the diversity of phytoplankton and their roles in primary production, the local food web and global export production. In addition to variations in size, different groups of phytoplankton exhibit different physiological and biochemical capabilities, "preferences" for nutrient utilization and growth form. For example, small cells, whether prokaryotic or eukaryotic, have the advantage of large surface to volume ratios and generally grow faster than their larger congeners or functional parallels at lower nutrient concentrations. With their simplified genomes, the most abundant picophytoplankton, Prochlorococcus, is generally unable to utilize nitrate, and apparently achieves its high cell abundance in the oligotrophic ocean by exploiting regenerated nitrogen. In contrast, diatoms, generally larger cells with larger more complex genomes, can grow nearly as fast and they achieve their highest growth rates on nitrate. Although stochastic factors – essentially, being in the right place at the right time – may determine which species dominates a bloom, similarities in some fundamental properties may be selective in defining a winning life form. For example, species able to escape microzooplankton predation because of their size (large cells) or protection (chemical or mechanical) consistently dominate the biomass in blooms . Size and functional diversity are important parameters in biogeochemical models, which are used to investigate the fate of carbon and nitrogen in the ocean. Differences in the physical regime of, e.g., the central gyres vs. the subpolar oceans, are reflected in differences in phytoplankton community composition in terms of size and taxonomy. Therefore we expect that global change that includes perturbation of the temperature and nutrient structure of the ocean will lead to changes in the phytoplankton community and the rest of the food web. Climate change and nitrogen fertilization of the open ocean are potential new drivers of phytoplankton biodiversity. Understanding the current structure and function of phytoplankton assemblages is thus essential to the effectiveness of models for predicting response of ocean productivity to global changes. Here we assign specific functions to major groups of phytoplankton that dominate the oceans largest biomes. Three major groups, the mamiellales, pyrmnesiophytes, and pelagophytes, dominate these ecosystems. Through comparative ecological genomics we contrast the evolution and ecology of these groups to the large phytoplankton cells that dominate coastal regions. Last Modified: 04/14/2015 Submitted by: Andrew E Allen This project has been registered at BCO-DMO: http://www.bco-dmo.org/project/544343 Molecular and diversity/genomic data has been deposited at BCO-DMO under: http://www.bco-dmo.org/dataset/565717 and linked to the project page above. This BCO-DMO entry includes results broken down by bacteria, archaea, eukaryotic chloroplast, and eukaryote. As noted in BCO-DMO, processed sequences from this data set can be found at http://scripps.ucsd.edy/labs/aallen/data/ under microbial diversity data sets. Other genomic data generated through this project has been deposited in the NCBI sequence read archive under accession SRX278429-SRX78432 and SRX278437. Last Modified: 09/22/2015 Submitted by: Andrew E Allen