Red tides happen when dinoflagellate algae populations increase and turn the water a shade of red due their red pigments. These algae consume oxygen in the water and release carbon dioxide and other acidic products that make the surrounding water acidic and hypoxic. These events are becoming more common with climate change. In fact, the most recent event off the coast of Sothern California occurred in 2020 and resulted in very low oxygen content and pH of the waters. Interestingly, researchers at the Scripps Institution of Oceanography use the local seawater for housing animals and found that captive white seabass were unusually tolerant of the hypoxic and acidic conditions. In a new study published in the American Journal of Physiology – Regulatory, Integrative and Comparative Physiology the researchers explored how these fish were able to regulate their cellular oxygen concentrations under such hypoxic conditions.
Despite their name, white seabass are actually a type of croaker. These fish get their name because of the croaking sounds the males make. They are also sought after by commercial and recreational fisheries (see image above). In fact, searching the term ‘white seabass’ in Google brings up quite a few recipes. It is not surprising, therefore, that these fish are important from an economic perspective. Their ability to tolerate hypoxic algae blooms also makes them important from a physiological perspective.
Red blood cells contain a molecule called hemoglobin, which is the primary oxygen carrier in the blood. Although its ability to bind oxygen is dependent on pH, some species can regulate the pH levels within their red blood cells with the help of special sodium-proton-exchanger proteins. The research team decided to explore whether this protein could protect oxygen binding to hemoglobin even during hypoxia in white seabass. They found that the sodium-proton-exchanger is located inside the RBCs and that it moves to the cell membrane in response to activation of stress-responsive pathways. Once in the plasma membrane, this exchanger can help protect oxygen binding to hemoglobin when levels of carbon dioxide are elevated resulting in an acidic environment. It was also activated by a drop in oxygen, but not to the same extent as a rise in carbon dioxide.
Understanding how animals respond to changes in their environment can help researchers understand how they will adapt (or not) to climate changes.
TS Harter, AM Clifford, M Tresguerres. Adrenergically induced translocation of red blood cell β-adrenergic sodium-proton exchangers has ecological relevance for hypoxic and hypercapnic white seabass. 321(5): R655-R671, 2021.