New Method Helps Predict How Individual Microalgae Might Behave Under Future Temperature Stress

Owing to the composition of their microalgae symbionts, coral species showcase different temperature tolerances.

At Uppsala University, with the availability of a new technique, scientists were able to forecast the behavior of separate microalgae under future temperature stress and determine highly tolerant coral symbionts.

Jointly with the approaching single cell selection and growth experiments, the identification of climate-resilient cells offers a chance to help reduce the impacts of coral bleaching.

Coral reefs tend to offer income and sustenance to approximately half a billion people, safeguard coastlines and attract tourists. They are among some of the most highly biodiverse ecosystems on the planet. In spite of their significance, over half of the world’s coral reefs are currently being subjected to stress, mainly as a result of climate change and related human activities.

Stressed or “bleached” corals explain the interruption of the symbiosis between corals and their photosynthetic partners. It is a heavily pigmented microalgae that offer the majority of the energy to its coral host.

This is the reason behind the white appearance of the coral skeleton (bleached) and leaves the coral in a form of energy shortage until new — probably less temperature-sensitive — symbiont cells are taken up from the surrounding.

Hence, the temperature sensitivity of a coral relies in part on the temperature sensitivity of its symbionts. This has made the analysis of temperature tolerance among coral symbionts an intense topic for research.

In a new study reported in the ISME Journal, researchers analyzed how various species of coral symbionts tend to react to temperature stress. The variation in temperature tolerance between various coral symbiont species was already a known fact. However, there are very few studies of the variation between individual cells inside the same species.

These differences among cells allowed us to predict the temperature tolerance of a cell before the stress actually occurred. For one, this might be handy for coral reef monitoring because it enables us to recognize more heat tolerant in a rapid, minimally-invasive assay.

Linhong Xiao, Study First Author, Uppsala University

Xiao added, “By providing the means to identify and select more temperature tolerant coral symbionts, the method also holds potential to accelerate ongoing coral reef restoration efforts by ‘experimentally evolving’ temperature tolerant coral symbionts which could, conceivably, be introduced back to coral host larvae in order to make corals more robust against climate change.”

Compared to studies that were performed earlier, this study utilized a special miniaturized method comprising a microscope and a credit card-sized “microchip” that accommodates several hundreds of individual coral symbiont cells to evaluate variations in temperature sensitivity among the single cells.

Adopting this special method made the scientists quantify that individual cells present inside each species tend to act in a different manner from their sister cells.

We hope our new method can help to predict the thermal tolerance of corals in the field by extracting and measuring symbiont cells from live corals. While we still have a long way to go, our tools might help coral-reef monitoring and also increase the speed at which we can create stocks of climate resilient coral symbionts, a frontier research area.

Lars Behrendt, Study Head, Uppsala University

Journal Reference:

Xiao, L., et al. (2022) Photophysiological response of Symbiodiniaceae single cells to temperature stress. The ISME Journal. doi.org/10.1038/s41396-022-01243-6.