| Due to anthropogenic emissions of CO2, the world's oceans are becoming more acidic. Ocean pH levels have decreased by 0.1 units since 1850 and are expected to decrease by another 0.3-0.4 units over the next 100 years. Predicting the impacts of ocean acidification on marine communities requires understanding the consequences for individual species and their interactions with other species. This change in pH is likely to have major effects on calcification, metabolic stability and larval development for a wide variety of organisms. Not all organisms are expected to be adversely affected, however, and it is predicted that some algal species may thrive in an acidified ocean environment. Due to respiration (especially at night) and photosynthesis during low tide, the pH of seawater in tide pools can vary dramatically throughout the day. This daily change is orders of magnitude more extreme than what is expected for the ocean at large over the next century. In order to examine how these communities may respond to this aspect of climate change, I exposed both natural tide pools and tide pool mesocosms to high CO2 conditions. To do this, I utilized yeast reactors to maintain low pH conditions within the range of natural pH variation seen in tide pools. Natural tide pools were used for field portions of the experiment, while split mesocosms were used in running seawater tables to examine species interactions. In response, the green alga Ulva increased in growth and cover under high CO2 conditions. High CO2 treatments also resulted in increased grazing by the herbivorous snail, Littorina littorea. Tissue analyses suggest that shifts in stoichiometry may be the reason for this behavioral shift. I also observed transient, but significant, decreases in metrics such as diversity, richness and evenness in natural tide pools following CO2 enrichment. As one of the first in natura studies of this issue, my work highlights the utility and importance of considering ocean acidification effects in a community context. |
