Intellectual Merit. Progressing ocean acidification and increasing sea surface temperature may significantly impact marine plankton community structure and community-level processes. Yet, our ability to predict specific responses is still limited because of the tremendous taxonomic complexity of microbial assemblages and the limitations of the methodological and experimental tools presently available to test specific hypotheses. Research to study community level effects due to a changing CO2/temperature regime often involve short-term field incubations that subject organisms to simulated 'greenhouse' conditions. A central question for understanding global climate change is whether the trends and patterns that are observed in communities during short-term manipulations can be extrapolated to the responses of fully acclimated plankton communities over decadal or longer timescales.
The specific objectives of this research program are: 1) to examine how protistan communities restructure in response to increased seawater CO2 concentrations and temperature in semi-continuous field incubation experiments, and 2) to evaluate if the dominant algal species that are isolated from either ambient or increased CO2 and temperature treatments in field experiments will re-establish dominance under the same conditions in acclimated laboratory culture competition studies. Changes in community structure of natural protistan assemblages in our experimental treatments will be followed using image-based methods (flow cytometry, FlowCAM and microscopy) in combination with state-of the art molecular tools (DNA fingerprinting). Molecular approaches have begun to reveal an incredible high diversity for marine microbes and stimulate debate in regard to the ubiquitous presence of a microbial 'Rare Biosphere'; that is, the presence of a huge number of species that are present at extremely small percentages of the total abundance of microbes, among a much smaller percentage of dominant ones. Little is known about the ecological significance of these rare species, and the investigators hypothesize that change in CO2 and temperature will select for some of these members that are inconspicuous under ambient conditions.
The unique aspect of this experimental approach is the combined use of field incubations that encompass entire natural microbial assemblages, with a series of laboratory culture competition trials that focus on the same groups of algae after extended acclimation, to evaluate the validity of short-term experiments that examine changing CO2 and temperature. First, field incubation experiments will be conducted to characterize changes in protistan community structure under ambient and future CO2/temperature regimes. Second, clonal algal strains will be isolated from dominant taxa in present day and greenhouse treatments, and cultivated for extended periods under their 'preferred' CO2/temperature conditions. Finally, mixtures of these acclimated strains will be competed against each other, to re-examine their responses to ambient and greenhouse conditions and compare them to the responses observed in the unacclimated field incubation experiments.
Broader Impacts. Two graduate students will make this project the focus of their Ph.D. research at USC, and undergraduate students will be involved in the field and laboratory work. Results from this research will be incorporated in lesson plans on microbial diversity and global climate change. Dissemination of data and results is planned on a project website. The PIs in this project also participate in an on-going, innovative, NSF-funded program (Centers for Ocean Science Education Excellence; COSEE-West) which focuses on personal involvement of faculty in a custom framework to allow an effective connection with K-12 teachers, thus improving math and science education in disadvantaged parts of Southern California.
Approximately a fourth of the Carbon Dioxide (CO2) released into the atmosphere is absorbed into the oceans. This increase in CO2 causes a shift in the ocean’s chemistry, essentially making it more acidic. This trend in progressing ‘ocean acidification’ paired with changes in other global climate parameters such as increases in sea surface temperature are predicted to significantly impact marine plankton community structure but also community-level processes. As algal community structure and productivity changes at the base of the food web so does the amount of energy that becomes available to large consumers within marine ecosystems including commercially important species such as shellfish or fish. Studies have begun to show that if single organisms are exposed to CO2 concentrations that resemble a future, more acidic ocean, they respond differently. For instance, some may grow faster, some slower, others yet appear unaffected. We still know little about responses on the community level to ocean acidification or the effects that multiple climate change parameters may have (e.g., increases in both CO2 and temperature). This study’s main objectives were to investigate how overall community structure and algal physiology are affected if mixed algal assemblages are exposed to ‘greenhouse conditions’ (predicted for 2100) in short-term experiments (~2 weeks). In addition, we wanted to evaluate if observed trends from 2-week experiments can serve as predictors for what can be expected for algal communities as they are exposed to a gradual increase of CO2 and temperature, in other words, as they experience shifts over the coming decades and are given time to acclimate. To address latter question, we first isolated the most common algal species from either ambient or altered CO2/temperature treatments at the end of the 2-week experiments and allowed the cultured organisms to acclimate to varying CO2/temperature conditions over extended periods of time (up to one year). Then, we recombined them to compare competition outcome with trends from the 2-week experiments. Our findings demonstrated that short-term experiments can serve as a good proxy for several algal species. Both, temperature and CO2 concentration, interacted strongly in affecting final community structure but temperature became a stronger driver especially when species were allowed longer periods to acclimate to increased CO2 levels (e.g., 4 compared to 8 or 12 months). We also found that some organisms were more resilient in handling environmental perturbation in general (‘weed species’) and their ability to establish dominance could not be directly attributed to their ability to handle pCO2 and/or temperature change. Finally, the importance of being able to analyze and resolve responses for individual members of the algal community during experimentation became clear as we demonstrated species-specific additive (synergistic) and antagonistic effects of CO2 and temperature on individual members of the algal community. So far, this project has resulted in nine peer-reviewed journal articles and several conference presentations. Two PhD students were supported through this research and several undergraduates participated in varying aspects of field work, sample processing and data analyses. Significant findings from this work are also incorporated into lesson plans and public outreach talks by the participating PIs. Normal 0 false false false EN-US X-NONE X-NONE
