b'6 Carnegie Science|Spring/Summer 2020Who Controls Whom:Algae or the Sea Anemone?According to new research led by Carnegies Shawna Foo, now at Arizona State University, when the sea anemone Aiptasia hosts symbiotic algae, it moves toward light. When the anemone is bleached, its movements lack directionality. Image courtesy Ken Caldeira, Carnegie Institution for Science B leached anemonesthose lacking symbiotic algaedo not move toward light, a behavior that healthy, symbiotic anemones do. Published in Coral Reefs, this finding from Carnegies Shawna Foo, Arthur Grossman, and Ken Caldeira, along with Lauren Liddell of the NASA Ames Research Center, is a case study to explore the concept of control in a symbiotic relationship. Anemones are closely related to coral and can help scientists understand coral reef ecosystems. Like corals, they host algae that convert the Suns energy into food through photosynthesis. The algae share some of the nutrients they produce with their anemone or coral hosts. Ocean warming due to climate change is causing coral and anemones to lose their algal tenants, a phenomenon called bleaching, Caldeira said. Anemones can capture their own food, but the nutrients provided by the photosynthetic algae allow them to survive when Shawna Foo is studying Aiptasia under blue light. there isnt much available to eatbeneficial in a changingImage courtesy Ken Caldeira, Carnegie Institution for Scienceclimate. But many corals will die without the nutrients provided by the algae they host.Grossman added: The algae have numerous light-sensitive This research revealed something new about bleachedreceptors absorbing light in the blue region of the visible anemones: they do not move towards light as healthy anemonesspectrum that might participate in this process; currently we do. They found that the anemone Aiptasia know almost nothing about the roles of such photoreceptors insensed and moved toward white and blue light when it was hosting algae. Butthese types of symbiotic algae.without an algal tenant (the symbiont), the anemones movementMore research is needed to understand the physiological was random and lacked directionality.mechanisms underpinning this observationhow the anemone This finding raises the question about whether theand algae signal each other to take actions that enhance the photosynthetic algae guide the anemone hosts movement, oralgaes ability to harvest energy from sunlight. whether the anemone has evolved to move toward the light inRegardless of how the relationship between the algaes the presence of its algal tenant.presence and the anemones movement functions, it is clear that It is possible that the algae are sensing the direction of thethe symbiotic pairing has evolved to take advantage of a situation light and subsequently controlling the anemones movement,that allows both partners to prosper, Caldeira concluded. which optimizes their absorption of light for photosynthesis andIt has been suggested that transplanting more thermally growth, explained lead author Foo, who is now at Arizona Stateresilient, non-native algae into coral could be a mechanism for University. Or perhaps itsurviving bleaching events. Understanding the signaling SUPPORT: is the anemones thatmechanisms facilitating the interactions between tenant and A Carnegie Science Venture Grant and the Gordon and Betty Moore Foundation supported this work. sense the light, but onlyhost, including this ability to sense and move toward light, could when populated by algae.help scientists in this research.'