Award: OCE-1220664

Copepods are the most important marine secondary producers world-wide, and they serve as a dominant food for nearly all larval fish and many sea birds and marine mammals. They make up 70-90% of the zooplankton biomass throughout most of the world?s oceans. Despite this, very few studies have addressed the impact of the emerging climate threat of ocean acidification (OA) on copepods. The existing studies have primarily focused on how OA directly affects copepods. Few significant effects of OA on copepods have been found, and almost no effects have been found at OA levels that are within realistic future predictions for the world?s oceans. However, there is increasing evidence that OA significantly affects biological characteristics and the nutritional quality of their dominant prey, the phytoplankton. For example, some researchers have shown that OA affects the types and concentrations of fatty acids produced by phytoplankton. This is important because the amount and types of fatty acids present in phytoplankton are crucial for the health and development rate of juvenile copepods. Some fatty acids essential to growth and survival of juvenile copepods cannot be synthesized by the mother copepods themselves, and instead must be acquired through the mothers? phytoplankton diets. If OA changes the nutritional quality of their food, then copepod grazing, egg production, and hatching success could also change. This could mean that copepod populations and, ultimately, marine food webs would also change. This award provided the opportunity to advance our understanding of how copepod populations are affected by OA. Our main objective was to determine how changes in phytoplankton physiology and biochemistry affect copepod reproductive performance and output. We also included a series of experiments that tested whether OA affects copepod reproductive output independent of changes to prey. A conceptual diagram showing the various pathways by which OA may affect copepods, and the pathways that formed the foundation of our hypotheses, is shown in Figure 1. Our results show that for the phytoplankton used in this study, OA indeed caused changes in phytoplankton that could alter copepod reproductive output. For example, all phytoplankton species tested under OA scenarios showed higher population growth rates compared to current ocean acidity levels. In two of the three phytoplankton tested, OA increased the total amount of lipids per phytoplankton cell, while one phytoplankton species showed an opposite trend, with lower lipid concentrations under OA scenarios. The biological changes we observed in the phytoplankton did give rise to some modifications in copepod behavior, reproductive output, and developmental rates of juvenile copepods. In the two copepods used in this study, a large lipid-rich, and a small lipid poor species, we observed differences in their feeding rates when offered phytoplankton grown under OA. For the small copepods, the developmental rate of copepod juveniles was faster when consuming phytoplankton grown under OA. For the larger copepod, the number of eggs produced by individual adult females was lower when feeding on phytoplankton grown under OA. These results show that the reproductive output and development of juvenile copepods can be affected by OA through the food quality of their prey, and that the degree to which this occurs is dependent on the individual species of copepods. Perhaps the most significant finding from this study is that female copepods that were feeding on lipid rich prey grown under OA conditions accumulated less fatty acids in their bodies than those eating prey grown at current ocean conditions. That is, the pattern was reversed in the copepods from what was observed in their prey. This result has implications for the efficiency of marine food webs. Specifically, it reduces the amount of these essential nutrients that are available to the animals that prey on these copepods. We were committed to broadening the scope of this project beyond just the research activities that most directly advance scientific understanding of OA effects on planktonic food webs. This award supported public outreach initiatives that increased awareness of marine issues in the general public through presentations by the faculty and students at public events. We collaborated with local schools to incorporate the concept of OA into K-12 school curriculums. Seven underrepresented multicultural students, mentored by the principle investigators of this project, showcased their research at national scientific conferences. All told, this award supported eleven undergraduate students conducting independent research projects, the research and academic costs for three graduate students, and the training and professional development of a postdoctoral researcher. Further, it increased research infrastructure and capacity at Western Washington University?s (WWU) Shannon Point Marine Center, which is in use for ongoing student research projects (graduate and undergraduate), and has been used in several undergraduate courses. This increased capacity serves to benefit all science, technology, engineering and math (STEM) students enrolled at WWU and regional community colleges. Last Modified: 03/29/2017 Submitted by: M. Brady Olson