Outreach | 2016 Society of Integrative and Comparative Biology

Anthopleura elegantissima participates in a facultative symbiosis with two microalgae Symbiodinium muscatinei and Elliptochloris marina. The symbiosis is centered around nutrient exchange including reduced organic carbon, inorganic nitrogen and carbon dioxide (CO2). The CO2 is used in algal photosynthesis and is produced in part by anemone carbonic anhydrase (CA) which catalyzes the reversible reaction of bicarbonate (HCO3-) to CO2. Under ocean acidification conditions, algal symbiont densities in A. elegantissima have been shown to increase, thereby increasing the demand for CO2 by the symbionts. Additionally, ocean acidification causes an increase in the abundance of HCO3- and CO2 in seawater. Therefore, we predicted that an increase in algal symbiont density under acidifying conditions would trigger an increase in anemone CA activity to meet the need for increased CO2. Aposymbiotic, Symbiodinium-, and Elliptochloris-containing A. elegantissima were collected from four locations around San Juan Island, and placed into ambient and high pCO2 conditions for ten days. Anemone CA activity was only measured after the experiment and algal densities were measured before and after the experiment. There was no significant effect of pCO2 or symbiotic state on the CA or density of algal symbionts after ten days of treatment. Our findings suggest that A. elegantissima may have internal homeostatic mechanisms to respond to increased pCO2 levels and concomitant increased algal densities.