A Changing Sea: the effects of temperature and CO2 to the temperate sea anemone Anthopleura elegantissima and its green symbiont Elliptochloris marina

• Main Author: Diep, Kimberly
• Format: Text
• Language: English
• Published: Western CEDAR 2017
• Subjects: Environmental Studies; Ocean acidification
• Online Access: https://cedar.wwu.edu/scholwk/2017/Day_one/13

Ocean acidification, which occurs as rising atmospheric CO2 reduces pH and changes the carbonate chemistry of seawater, is likely to change marine ecosystems. Calcifying organisms are clearly at risk, but non-calcifying, photosynthetic organisms could actually benefit from high CO2 conditions. Elliptochloris marina is a unicellular alga that engages in and endosymbiosis with the temperate sea anemone Anthopleura elegantissima. Little is known about how temperature and elevated CO2 will affect either partner in this non-calcifying cnidarian. A. elegantissima hosting E. marina were exposed to three concentrations of CO2 (400 μatm, 800 μatm, or 1200 μatm) at 12 or 20°C in a laboratory setting for 5 weeks. Sea anemone appearance and behavior, and photosynthetic efficiency and density of the symbionts were used to assess the health of the host, symbiont, and the symbiosis. Over 5 weeks of observation, there was no clear effect of temperature or CO2 on behavior of the sea anemones (measured by expansion of the tentacle crown). Anemones in the 20°C treatment appeared to be bleaching over the course of the experiment, but, by the end of 5 weeks, there was no statistically significant difference in symbiont density. There was also no significant effect of temperature, CO2, or the interaction between temperature and CO2 on symbiont photosynthetic efficiency. Our results show that a relatively short exposure to high seawater pCO2 and elevated temperature had no direct negative effect on A. elegantissima or E. marina. However, these conditions may impact the competitiveness of E. marina compared to another endosymbiont A. elegantissima hosts, which responds very positively to high CO2 and could lead to important changes in the ecology of this important intertidal species.