University of São Paulo: Brazilian corals resort to “jeitinho” to resist ocean warming

The ability to adjust to new environmental conditions makes the corals of the Brazilian coast more tolerant to bleaching, a phenomenon triggered mainly by the increase in ocean temperature. “When exposed to a simulated climate change scenario, in the laboratory, with a temperature increase of 2.5ºC [heating] and a decrease of 0.3 pH unit [acidification] , coral species from the Brazilian coast responded positively to these conditions. , which suggests an evolution of physiological responses driven by the waters, rich in nutrients and organic matter and with lower luminosity due to the flow of sediments from the Brazilian coast”, he explains to Jornal da USPthe biologist and research coordinator Samuel Coelho de Faria, professor at the Center for Marine Biology (Cebimar) at USP and an associate researcher at the Coral Vivo Project. According to him, the ability of corals to be plastic is a ‘Brazilian way’ for our coral fauna to be tolerant of climate change. The region (the Brazilian coast) is being seen as a great refuge of tolerance to the impacts of climate change, deserving priority in public policies of environmental conservation.

The comparative experimental study included eighteen species of corals (17 scleractians and one hydrocoral) originating from the Brazilian coast and the Sargasso Sea (Bermuda), located in the Atlantic Ocean, near the east coast of the United States (USA). “Both regions host similar species of corals in evolutionary terms, but they present different physicochemical characteristics in their waters, especially with regard to the amount of nutrients and availability of light”, says the researcher.

According to the study, ecosystems that involve coral reefs are essential for the maintenance of aquatic biodiversity. They are sources of food, shelter and protection for many species and about 25% of all oceanic biodiversity is sheltered by coral reefs. The degradation and depletion of these resources will have negative repercussions for the whole of society, he reports. Numerous reef-dependent species serve as sources for medicines and biochemical agents, in addition to moving more than 30 billion dollars a year in goods and services such as fishing, tourism, food, medical and technological development and coast protection. Reefs provide a complex web of interactions, with direct impacts, therefore, on the terrestrial environment of which we are a part, says Professor Faria.

Bleaching is a natural defense response of corals to situations of thermal stress, reports Miguel Mies, an associate researcher at the Oceanographic Institute (IO) at USP and the Coral Vivo Project. The phenomenon, which is due to global warming, has been happening in several parts of the world, but some studies have shown that Brazilian corals are less affected. An article signed by Mies with other authors published in Frontiers brings data that show that the coral reefs of the South Atlantic are the main refuges of global warming and less susceptible to bleaching. To understand the reasons that make Brazilian corals more tolerant of the increase in sea temperature that can lead to their death, Professor Faria explains physiological aspects of corals.

Symbiotic relationship of corals with zooxanthellae
Corals are marine animals, and many species perform photosynthesis because they have a symbiotic relationship with intracellular microalgae called zooxanthellae. In shallow water with access to light, these microalgae meet up to 98% of the energy demands of the host coral, also contributing, in part, to their peculiar color. In turn, zooxanthellae survive and grow thanks to the products generated by the coral’s metabolism, especially nitrogen compounds, in addition to receiving shelter, protection and a stable position in the water column for access to light. The energy provided by photosynthesis and performed by zooxanthellae is also responsible for supplying the highest rates of calcification of corals, in the formation of the skeleton, whose structure is composed of calcium carbonate.

In episodes of bleaching caused by the heating of the waters, the corals, by a defensive action, expel the zooxanthellae from within their tissues because they become sources of large amounts of reactive oxygen species that trigger oxidative stress, substances that diffuse through the tissues of the host coral. As a consequence, these animals lose the ability to be fueled by photosynthesis and become translucent by the loss of symbionts, exposing the white color of their underlying skeleton.

Brazilian waters: turbidity rich in sediments and nutrients
Mies explains that the oceanic waters of the Brazilian coast have very different characteristics from other regions. They are rich in nutrients and sediments from the Brazilian coast, which reach the sea through its tributaries. According to the researcher, the coral fauna that developed here has low diversity, a high degree of endemism (typical of this region) and is quite tolerant of these adverse conditions. The Sargasso Sea, unlike Brazilian waters, has crystalline waters and low levels of nutrients and organic matter.

The corals were transported inside boxes with seawater to the respective research bases at Projeto Coral Vivo (Porto Seguro, Bahia, Brazil) and Bermuda Institute of Ocean Sciences (St. George’s, Bermuda), where they were acclimatized for 21 days. in aquariums, in an open system and continuous flow with seawater. Light, temperature and pH were kept constant, with the exception of the physicochemical characteristics of the water, which were typical for each region.

After acclimatization, the corals were subjected to a simulated temperature increase of 2.5ºC and a reduction of 0.3 pH unit of water for 14 days. Under these conditions, coral species in Bermuda suffered bleaching (loss of zooxanthellae and chlorophyll) after being exposed to the climate change scenario. The Brazilian species, on the other hand, demonstrated a compensatory effect in terms of chlorophyll content and antioxidant capacity.

The researchers observed that both the Bermuda and Brazilian species showed a reduction in the density of symbionts (zooxanthellae) of around 30%. “This means that, on average, species from both locations expelled the zooxanthellae after the simulated temperature and pH treatment”, says the researcher. However, corals from Brazil showed an average increase of up to 90% in chlorophyll content, which means that the concentration per cell of zooxanthella increased up to seven times. Faria explains that zooxanthellae off the coast of Brazil were able to increase chlorophyll content in the face of environmental stressors, a response conceptualized as symbiotic plasticity.

antioxidant system
Regarding the defense system, under natural conditions, the antioxidant capacity of the Bermuda species is about ten times greater than that of the Brazilian species. However, when exposed to the simulated scenario of increasing temperature and decreasing pH, only species from Brazil were able to increase antioxidant defenses, an average increase of 40%, which suggests that they deal better with induced oxidative stress, says Faria. This compensatory effect is an adjustment capacity of Brazilian species in the face of new environmental conditions, a concept called antioxidant plasticity.

As for coral calcification levels – an index that indicates health conditions and energy availability for growth – the study showed that there was also an average increase of 15% in Brazilian species and an average reduction of approximately 10% in Bermuda species, indicating that the growth of Brazilian corals was not negatively affected.

Symbiotic and antioxidant plasticities seem to support higher levels of calcification in species from the Brazilian coast, reports Faria. “The research not only confirmed the hypothesis of greater physiological tolerance of Brazilian species in the face of climate change, but also verified a co-evolution of symbiotic and antioxidant plasticities in the South Atlantic. The ability to respond positively to chlorophyll content and antioxidant defenses in the face of induced treatment evolved in an integrated and convergent manner in Brazilian species, a relationship driven by the emblematic nutritional and luminous nature of our Brazilian waters”, he concludes.

The institutions involved in the research were USP (Cebimar, Institute of Biosciences and Oceanographic Institute), Bermuda Institute of Ocean Sciences, University of California, Riverside Smithsonian Tropical Research Institute, Federal University of Rio de Janeiro and the Federal University of Rio Grande (Furg ).

Climate changes
In February, the Intergovernmental Panel on Climate Change (IPCC) released a new report on global warming with warnings of irreversible impacts for humanity if decisions are not taken in the next two or three decades to reduce the emission of greenhouse gases ( CO2, CH4, N2O, HFCs, PFCs and SF6) that prevent the loss of terrestrial heat and keep the planet warm.

According to the document, which compiles and synthesizes studies by thousands of scientists, the world warmed an average of 0.85°C between 1880 and 2012. The last three decades were the warmest since 1850. The increase in temperature between the average of the period 1850 -1900 and the average for the period 2003–2012 was approximately 0.78°C.

The oceans have accumulated most of this heat, serving as a buffer for the warming of the atmosphere, storing more than 90% of the climate system’s energy and much of the carbon dioxide. The sea is becoming more acidic (less alkaline) by the continued absorption of carbon dioxide.

According to the report, if emissions continue on current trends – warming will increase, reaching 4.8°C by 2100 -, the negative effects will multiply and disrupt all components of the climate system, with serious repercussions for the good. -being of humanity and all other life forms.

Commenting on the IPCC report, Miguel Mies regrets that humanity is not managing to stop global warming and that, as a result, in a short time, perhaps three decades, if nothing is done, coral reefs will be lost. “Heating only 1.5ºC or 2ºC does not meet the needs of coral reef protection. They will perish long before that scenario,” he says.

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