Award: OCE-1851412

This project sought to understand how widespread gelatinous filter feeders influence populations of microorganisms in the oceans. We approached this problem through integrating techniques across multiple biological scales, including bluewater SCUBA, oceanographic sampling, cellular, and molecular analysis. We also trained undergraduate and graduate students in oceanography and scientific thinking and used our research products in science and technical writing courses to reach a wider audience. Through the project, we revealed the interaction between the oceans most numerous cells, bacteria, and five different types of predators including pyrosomes, doliolids, appendicularians, salps, and pteropods in four different publications. We found that each grazer consumes larger phytoplankton such as diatoms as well as the dominant marine cyanobacterium Synechococcus. However, we found that some of the oceans most dominant cells, the cyanobacterium Prochlorococcus and the bacterium SAR11, seem to escape grazing by these organisms. Overall, these results demonstrate several important points. 1) Gelatinous zooplankton grazers feed selectively, so their feeding can shape microbial community structure in the ocean by removing some members of the community and leaving others in place. This selection likely has a role in shaping the function of microbial populations in the ocean on global scales. 2) Different gelatinous grazers prefer different microbial prey. We saw this when we compared different taxa of grazers and their microbial prey from the same waters. Pyrosomes and doliolids are one notable example. Pyrosomes prefer to consume larger diatoms over Synechococcus, but coexisting doliolids preferred Synechococcus. These results demonstrate that the feeding preferences of each grazer needs to be understood independently of the others, and that feeding mechanism may determine prey selection. 3) While previously understudied because of their fragility, our work and the work of others is now gathering momentum and revealing a major role for these animals in controlling the community and function of the oceans microbial populations. This information can be incorporated in ecosystem models to better predict how the ocean will change in response to disturbances, seasonal, and longer-term change. Finally, we synthesized our new understanding with the work of others. Through this project, we bridged disciplines that are often siloed, including zooplankton biology and microbial ecology. Our collaboration brought these two perspectives together towards improved understanding of marine systems holistically. This project also synthesized the existing data to create new comparisons of the feeding rates of different grazers on different marine microbes. This analysis shows a huge gap in attention on smaller cells, despite their outsized impact to global ocean processes, and provides a road map for future work. Finally, the synthesis of these past studies and ours reveals an important role of mucous mesh grazers in the microbial loop. We present a hypothesis that mucous grazers short circuit the microbial loop by making microbial carbon available to the highest trophic levels in one feeding interaction. Overall, this project advances oceanography by bridging disciplines, synthesizing existing studies, and presenting evidence that gelatinous zooplankton are important microbial predators. Last Modified: 12/20/2023 Submitted by: AnneWThompson