Environmental stress and signaling based on reactive oxygen species among planktonic protists

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Traditionally marine food webs have been studied on the basis of size, assuming that larger organisms eat smaller ones, and that they eat everything in a given size range. This simplification has not stood the test of time, especially for the smallest microbial plankton. Not only do smaller organisms sometimes eat larger ones, there is growing evidence that chemical signaling and defenses are acting at these small scales. This project addresses the central premise that the oxidative stress response is an emergent property of phototrophic cellular systems, with implications for nearly every aspect of a phytoplankton cell's life in the upper ocean. Oxidative stress (OS), arising from numerous environmental stressors, can damage cells and lead to release of compounds suspected to be potent signals regulating protist behavior. Through chemical signaling, OS is hypothesized to govern relationships among environmental variability, phytoplankton condition, and protist predation. The study of these integrated processes has three overarching objectives: 1) Use light stress to create oxidatively stressed phytoplankton in the laboratory, and characterize the response using an array of fluorescent probes, biochemical measurements, and physiological assays. In addition, production and release of potential signal molecules will be quantified. 2) Examine protist predation and behavioral responses to oxidatively stressed phytoplankton and associated chemical signals. Responses will be investigated by means of manipulation experiments and resulting signal chemistry. 3) Investigate the prevalence of OS, its environmental correlates, and the microzooplankton predation response in a local embayment. Broader impacts will build directly on these experimental and observational activities. The project will support several graduate students and involve undergraduates through two programs at Shannon Point Marine Center, including one targeting under-represented minorities. Funds will support a significant collection of heterotrophic protists isolates. The fluorometer will be used in developing new units for at least 3 different Western Washington University marine-related courses. In addition, graduate students will use protist images as the basis for outreach activities aimed at the general public and K-12 students.This research will help to elucidate some of the many ways in which the OS response can affect phytoplankton fitness, characterizing the position of key coastal species along an OS response spectrum. Findings will also inform the relatively new and exciting field of chemical signaling in planktonic communities. Finally, this study will help elucidate the links between environmental stress, phytoplankton response, and predation in planktonic ecosystems. These links relate to central issues in biological oceanography, including the predator-prey interactions that influence bloom demise, and the mechanisms by which protists feed selectively and thereby structure prey communities. The research is a cross-cutting endeavor that unites subjects usually studied in isolation through a novel conceptual framework. Outcomes have the potential to generate broadly applicable insights into the ecological and evolutionary regulation of this key trophic link in planktonic food webs.