Award: OCE-0962309

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.

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