Award: OCE-1558490

Our overall goal was to examine how single-celled marine photosynthetic microbes, called diatoms, thrive across very different environments, from the coast to the open ocean. Diatoms generate about 20% of global primary production and are key contributors to the cycling of major elements like carbon through the earth-atmosphere system. We asked the following questions: ● How variable is diatom community composition along the coast compared to the open ocean? ● How do diatom species regulate their cellular activities in vastly different environments? ● How does the availability of nutrients alter diatom community composition and cellular activity? We conducted two oceanographic cruises in the North Atlantic, sampling from the NE coast of the US, a region rich in nutrients, to Bermuda, located in the nutrient limited Sargasso Sea. We first examined diatom species diversity and found no significant differences in diversity with environment. Instead, we found that some species were located primarily in coastal regions while others were found only in the open ocean, suggesting that they are adapted to different environmental conditions. Interestingly, a subset of species was found in both types of environments suggesting that these species are 'flexible' and able to cope with a wide range of environmental conditions. Second, we analyzed the cellular activities of diatoms by examining their gene expression, which is essentially a read out of all the genes in the genome. This approach provides a quantitative assessment of gene expression of organisms sampled directly from the natural environment, providing a 'read out' of their activities. Because little is known about diatom activities from the open ocean, we generated a custom database of open ocean gene expression using diatoms we grew in the laboratory. We then used this database to ask questions about the gene expression of diatoms sampled from either the open ocean or coastal waters. Generally, we found that gene expression was more strongly tied to the taxonomic affiliation of the organisms than to the oceanographic region we sampled. We did identify an exception to this pattern where some species had particularly strong responses to environmental variation. Finally, we also found large differences in gene expression among diatom species, suggesting that species-specific adaptations may help explain why diatoms can generate so much primary production in the world's oceans. Broader impacts of the project included support for one female PhD student, two postdoctoral researchers (one female) and three undergraduates. Our work included educating ~750 K-12 students about STEM careers and oceanography through various programs including the Narragansett Bay Classroom After School Science program, the Overbrook Academy STEM careers day, the Girl Scouts of Eastern Massachusetts STEM Conference and EXPO and the Science and Math Investigative Learning Experience (SMILE) Fourth Grade Ecology Day. Our outreach and education work also included yearly participation in the Metcalf Institute Summer Journalism Workshop that included interactive workshops on how science is done to over 60 professional journalists. Other activities included mentoring for the URI chapter of the Society of Women in Marine Science (SWMS), over 20 contributions to the ocean.bites blog (200-400 views per day) and outreach booths at large public events like the Volvo Ocean Races Ocean Exploration Zone (~40,000 visitors). Last Modified: 12/17/2021 Submitted by: Tatiana Rynearson