The investigator will study the cellular mechanisms of how reef-building corals sense changes in pH in the surrounding seawater and how the regulation of this pathway affects coral physiological responses to ocean acidification (OA). This project builds on the recent discovery that a bicarbonate (HCO3-) sensing enzyme (soluble adenylyl cyclase [sAC]) involved in the regulation of pH homeostasis in vertebrates is expressed in corals. This enzyme produces cAMP, a universal messenger molecule used in organisms from bacteria to mammals. The investigator's hypothesis is that the sAC pathway is involved in coral pH sensing and regulation of pH homeostasis through the production of cAMP. Coral sAC is stimulated in response to HCO3- concentrations relevant to coral physiology, and differences in sAC activity and regulation will affect coral physiological responses to OA.
To test her hypothesis, the investigator will: 1. Characterize the activity and expression of the sAC pathway and its response to CO2, HCO3- and pH in multiple coral species, 2. Determine how the sAC pathway affects coral physiology, including maintenance of pH homeostasis, respiration, photosynthesis, and calcification, 3. Determine how chronic exposure to projected OA conditions affect the regulation of the sAC pathway in corals and how these differences affect coral physiology.
The broader impacts of the project include developing a bilingual, multimedia exhibit showcasing the significance of ocean acidification and its effects on the marine environment at the Birch Aquarium in San Diego, reaching a large Latino population, and mentoring two female doctoral students and undergraduates.
This project is supported under the NSF Ocean Sciences Postdoctoral Research Fellowship (OCE PRF) program, with goals to support novel research by early career scientists and increase the diversity of the U.S. ocean sciences workforce and research community. With OCE-PRF support, this project will enable a promising early career researcher to establish themselves in an independent research career related to ocean sciences and broaden participation of under-represented groups in the ocean sciences.
Coral reefs around the world are threatened by global climate change, and of particular concern is the ability of corals to cope with ocean acidification. In order to understand how corals will respond to ocean acidification, we have investigated the cellular mechanisms that corals use to sense and regulate changes in pH. One pH regulation pathway that we have identified and characterized involves the acidification of the microenvironment where the endosymbiotic algae reside (Figure 1) by a coral proton pump, which is present in the host membrane surrounding the algae. Acidification of the algal microenvironment by the host coral promotes photosynthesis, demonstrating that corals can actively regulate symbiont physiology. Coral growth and calcification is supported by the sugars produced from algal photosynthesis, and this novel pathway is thus critical for the maintenance of the coral-algal symbiosis and likely coral survival on the reef. The second pathway that we have characterized during this project is involved in sensing changes in pH within coral cells by the enzyme soluble adenylyl cyclase (sAC). This enzyme is stimulated by bicarbonate to produce the universal signaling molecule cAMP, which can lead to a variety of downstream physiological changes. We demonstrated that corals express an active form of sAC throughout their tissues, as well as the nuclei of various cells, indicating sAC activity may influence gene expression. Inhibition of sAC activity leads to the breakdown of acid/base homeostasis within the calcifying cells and the extracellular calcifying fluid, suggesting that sAC activity is an important part of maintaining pH and therefore may be critical for promoting calcification. We expect that sAC plays an important role in detecting pH changes in the seawater due to ocean acidification, and through the production of cAMP helps cells compensate for the decreasing external pH. The physiological mechanisms that we have characterized during this project are an important step forward for coral biology and coral reef conservation. By improving our understanding of these how corals detect and regulate their internal and external pH environment, we can better predict if corals will be able to adapt to ocean acidification. These insights can be used to implement science-based management strategies to help protect sensitive species as well as hardy species with the potential to survive in the face of the multiple stressors that are impacting coral reefs around the world today.
