Coral reefs are among the most diverse and productive ecosystems on Earth, but they are also under threat from climate change, pollution, overfishing, and other human activities.
One of the most visible signs of coral stress is bleaching, which occurs when corals expel their symbiotic algae (zooxanthellae) or lose their pigments, turning white or pale.
Bleaching can lead to coral death or reduced growth, reproduction, and resistance to disease.
Scientists have long suspected that bleaching is triggered by the production of reactive oxygen species (ROS), a group of highly reactive molecules that can damage cellular components and cause oxidative stress.
ROS are generated by the zooxanthellae as a byproduct of photosynthesis, especially when exposed to high light and temperature conditions.
However, measuring ROS levels in corals has been challenging, as conventional methods require invasive sampling or laboratory experiments that may alter the natural conditions of the corals.
The sensor is based on a chemical compound called Amplex Red, which reacts with hydrogen peroxide (H2O2), one of the main forms of ROS, to produce a fluorescent product.
The sensor can be attached to a coral colony and measure the fluorescence intensity, which reflects the H2O2 concentration, using a fiber optic cable and a spectrometer.
The researchers tested their sensor on two species of corals, Acropora sp. and Porites sp., in the Red Sea, where they experience high light and temperature conditions during the summer.
They found that both species produced H2O2 in response to light, with higher levels during midday than in the morning or evening.
They also observed that Acropora sp. produced more H2O2 than Porites sp., which may explain why Acropora sp. is more susceptible to bleaching than Porites sp.
The researchers also compared their sensor measurements with conventional methods, such as colorimetric assays and enzyme-linked immunosorbent assays (ELISA), and found good agreement between them.
The sensor is the first of its kind to measure ROS levels in corals in situ, and it offers several advantages over existing methods.
It is non-invasive, as it does not require coral tissue sampling or manipulation. It is also fast, accurate, and sensitive, as it can measure H2O2 concentrations in real-time and at nanomolar levels.
Moreover, it is versatile, as it can be used on different coral species and in different environments.
It can help to elucidate the mechanisms and thresholds of ROS production and detoxification in corals, and how they vary among different coral species, symbionts, and environmental conditions.
It can also help to monitor the health and resilience of coral reefs and to identify the factors and locations that are most vulnerable to bleaching events.
The sensor can also contribute to coral conservation and restoration efforts, as it can provide information on the optimal conditions for coral growth and survival, and the best practices for coral transplantation and acclimatization.
For example, the sensor can help select the most resilient coral species and symbionts for reef rehabilitation and to adjust the light and temperature regimes for coral nurseries and aquaria.
The sensor is not only useful for corals, but also for other marine organisms that host zooxanthellae, such as giant clams, sea anemones, and sponges.
These organisms also produce ROS and are affected by bleaching, but they have been less studied than corals. The sensor can help to fill this knowledge gap and to understand the diversity and complexity of the coral-algal symbiosis.
A deeper understanding of coral bleaching
The sensor developed by the researchers is a breakthrough in coral research, as it allows for the first time to measure ROS levels in corals in situ and to explore their role in coral bleaching and stress response.
It can provide new insights into the physiology and ecology of corals and their symbionts, and their adaptation and acclimation to changing environmental conditions.
Moreover, it can support coral conservation and restoration efforts, by providing information on the health and resilience of coral reefs, and the best strategies for their protection and recovery.
In conclusion, the sensor is a powerful tool for advancing our understanding of coral bleaching and for safeguarding the future of coral reefs.
