Western CEDAR

Anemones on acid: possible benefits of ocean acidification to sea anemone-algal symbiosis

Ocean acidification continues to be a threat to most species of marine life and is projected to become more severe over the next 50 years. Areas that experience upwelling of low pH water, like the Salish Sea and Puget Sound, are particularly susceptible to even greater OA conditions. While much of OA literature has focused on the negative impacts to calcifiers, economically important shellfish, and zooplankton, not all species may be threatened by OA. Photosynthesizing organisms have shown some benefits from the increased CO₂ in their environment. This study focuses on one of the most abundant intertidal organisms in the Pacific Northwest, the aggregating anemone (Anthopleura elgantissima) and the two photosynthetic symbionts they house- Symbiodinium muscatinei and Elliptochloris marina. Anemones hosting each symbiont individual and those hosting both or none at all were subjected to 3 different levels of OA over the course of 10 weeks. Photosynthetic efficiency, reactive oxygen species (ROS), and CZAR score (the percent of organic carbon received from the symbiont) were measured during the experiment for all 4 symbiont states. Reactive oxygen species increased with OA level and was greatest in S. muscatinei anemones. Photosynthetic efficiency increased in intermediate levels of OA for both symbiont types but declined at the highest levels. CZAR score increased with OA level but was significantly higher in S. muscantinei anemones. Lastly, anemones that started with 50% of each symbiont type shifted toward a higher percentage of S. muscatinei with increased OA. This study suggests anemones hosting S. muscatinei may have a competitive advantage under future conditions and even benefit from increased OA until a certain threshold is reached.