A team comprising dozens of scientists embarked on a mission to find a solution to how coral reefs can survive climate change.
The scientific community has long looked to the past for inspiration. Echoing the spirit of explorers from the 19th and 20th centuries, the Tara Pacific expedition embarked on a mission not unlike those of old.
They sought to discover and understand the unknown. Over a period of two years, their quest led them across the vast expanse of the Pacific Ocean. The mission: to investigate the mysteries of coral survival.
The Tara Pacific expedition comprised an international team of 70 scientists from eight different countries. They made the voyage across the Pacific with an ambitious objective in mind.
Their goal was to gather the largest ever genetic dataset from a marine system. This mission specifically focused on coral reefs.
During the expedition, the team collected around 58,000 samples from a hundred different coral reefs. Their immense effort resulted in the assembly of an unparalleled genetic inventory.
This massive collection, recently published in Nature Communications, is openly accessible to scientists around the world. The expectation is that this dataset will serve as a fundamental resource for understanding coral habitats. It will also help to aide their goal of boosting coral reef survival amidst climate change for years to come.
The initial analysis of the gathered data revealed some eye-opening findings. Firstly, global microbial biodiversity is significantly higher than previously estimated. Secondly, environmental influences on evolutionary adaptation vary from species to species. Lastly, there appears to be duplication of key genes in corals.
Coral reefs, although they occupy a meager 0.16 percent of the world’s oceans, boast an incredibly diverse range of marine life. About 35 percent of known marine species make their home in these vibrant underwater ecosystems.
The team of researchers used a genetic marker-based dataset. They discovered that the microorganisms living in these reefs encompass the entirety of estimated global bacterial biodiversity.
“We have been completely underestimating the global microbial biodiversity”, proclaimed Christian Voolstra. He is a professor of genetics of adaptation in aquatic systems at the University of Konstanz.
Voolstra also the scientific coordinator of the Tara Pacific expedition. He suggested that the current estimation of biodiversity, around five million bacteria, may in fact be ten times lower than the real figure.
Scientists analyzed 32 archipelagos. These are all natural laboratories providing a diverse set of environmental conditions. This enabled them to explore the relationships between environment and genetic factors across vast geographical scales.
Their research shed light on how environmental influences on the evolutionary adaptation of corals differ depending on the species. This finding was made possible through an examination of telomeres. These are the ends of chromosomes carrying genetic information.
Much like in humans, where telomere length shortens with age and cell divisions, telomere length in corals also appears to have significant implications. The research team discovered that in highly stress-resistant corals, the telomere lengths remain constant. “They apparently have a mechanism to preserve the lengths of their telomeres,” concluded Voolstra.
In contrast, stress-sensitive coral species, typically with a shorter lifespan of about a hundred years, have telomere lengths that respond to environmental stress factors such as temperature changes.
Voolstra emphasized the potential implications of this finding, stating, “A direct imprint of environmental stress levels on organismal resilience may even hold implications for human health.”
Another critical discovery was that the longevity of some coral species could be attributed to the duplication of specific genes. These genes, deemed important, are found multiple times within the coral genomes.
The scientists were able to identify this phenomenon using a cutting-edge technique called long-read sequencing. This technique allows not just for the identification of present genes, but also the understanding of their order within the genome.
The widespread occurrence of gene duplication could be a reason why corals, despite being exposed to extreme environmental conditions like high UV radiation, are able to live for thousands of years, according to Voolstra.
The Tara Pacific expedition’s research will likely be a cornerstone for large-scale studies on coral reef diversity for many years ahead. One of the distinctive features of this expedition was the uniform methodology used at all the sampled locations over the two-year period. This ensured that the resulting data is fully comparable.
What makes this program truly special is its commitment to openness. All the datasets are freely available and accompanied by comprehensive physical and chemical measurements.
Voolstra lauds this unique aspect of the expedition, stating, “It is the largest dataset collection on coral reefs ever collected and it is completely open access.”
The hope is that this groundbreaking collection will serve as a foundation for the continued study of coral reefs worldwide, fueling scientific advancement for many years to come.
Coral reefs, often dubbed as the “rainforests of the sea,” are some of the most biodiverse ecosystems on our planet. They cover less than 0.2% of the ocean floor, but they support about 25% of all marine species. However, these vital ecosystems are facing an existential threat from climate change.
One of the most noticeable impacts of climate change on coral reefs is coral bleaching. Corals have a symbiotic relationship with microscopic algae called zooxanthellae. They live in their tissues and provide them with most of their food and color.
When water temperatures rise due to global warming, corals get stressed and expel the zooxanthellae. This causes them to turn completely white.
This is known as coral bleaching. Bleached corals are not dead, but they are under more stress and are more likely to die.
Another major impact of climate change on coral reefs is ocean acidification. The oceans absorb about a quarter of the carbon dioxide (CO2) that humans release into the atmosphere.
When CO2 dissolves in seawater, it forms carbonic acid and lowers the ocean’s pH. This makes it more acidic. This process is called ocean acidification.
Coral reefs are made of calcium carbonate, and acidified seawater makes it more difficult for corals to build and maintain their skeletons. This impedes reef growth and makes the reefs more susceptible to erosion and damage from storms.
Climate change also causes sea-level rise, which can affect coral reefs. If sea levels rise too quickly, deeper water can smother corals.
On the other hand, if sea levels rise too slowly, corals may grow above the water surface. This would then expose them to air, sunlight, and extreme temperatures, which can harm them.
Climate change may also lead to more frequent and intense storms. Storms can cause physical damage to coral reefs, breaking them apart and scattering the coral.
Warmer water temperatures are also linked to increased outbreaks of coral diseases, which can cause mass mortality events on reefs.
While the situation is critical, it’s not without hope. Coral reefs are remarkably resilient, and if given a chance, they can recover from bleaching events and other disturbances.
However, reducing greenhouse gas emissions is crucial to slowing the rate of global warming and ocean acidification. Additionally, protecting reefs from local stressors such as pollution and overfishing can improve their resilience to climate change.
Furthermore, scientists are researching ways to help corals adapt to changing conditions. These include breeding heat-tolerant coral varieties and developing innovative restoration techniques.