Deep beneath the waters of the Galapagos Marine Reserve (GMR) and atop a submerged volcano, an ancient coral reef was just discovered by an international group of scientists. It’s the first to be documented inside the protected area since it was established in 1998. Stretching out for several miles, the reef supports a breathtaking mix of marine life.
This finding comes at an opportune time. In the face of global warming and other environmental changes, corals in the Atlantic Ocean have declined precipitously in recent years, while corals in the Pacific and Indian Oceans are faring a bit better. That’s good news for this Galapagos treasure. And, by developing a method for describing several species of symbiotic algae that corals need to grow, a group of researchers has found that such mutualistic relationships in the Indo-Pacific may be more flexible and ultimately more resilient to higher ocean temperatures than those in the Atlantic.
Too, when it comes to preserving the world’s coral reefs, we’re finding out that what’s going on above the surface is just as important as what’s going on below.
Ancient corals uncovered
The Galapagos Deep 2023 expedition explored the uncharted depths of the Galapagos Marine Reserve with the deep-sea submarine Alvin. Twenty-one scientists participated in the voyage, which began on March 27 and ended on April 22. It was the first time Alvin had undertaken research dives inside the Galapagos Marine Reserve.
After the groundbreaking discovery of the ancient coral reef, Ecuador’s Minister of Environment Jose Antonio Davalos stated that the news reaffirms the nation’s determination to establish new marine protected areas in Ecuador and to continue promoting the creation of a regional marine protected area in the Eastern Tropical Pacific. The richness of the yet-explored depths of our ocean, he said, is another reason to strive towards achieving the commitments of the Global Ocean Alliance 30 x 30 initiative, which aims to safeguard at least 30 percent of the world’s oceans by 2030, aligning sustainable economic activities with conservation.
The discovered reef is novel for two main reasons: 1) it shows that sheltered, deep-water coral communities have likely persisted for centuries in the depths of the GMR, supporting diverse, rich and potentially unique marine communities; and 2) in shallow reefs where finding 10 to 20 percent of coral cover would be considered a relatively unhealthy reef, in the deep sea this is the norm. Dead coral skeletons making up the remaining 80 to 90 percent still provide homes for a huge diversity of life, which is less reliant on the live sections of coral. However, the ancient reef just found has 50 to 60 percent live coral in many areas, which is very rare. It’s pristine and teeming with life: batfish, pink octopuses, squat lobsters and an array of deep-sea fish, rays and sharks.
This newly discovered reef is of potential global significance, a site we can monitor over time to see how an untouched habitat evolves with our current climate crisis. Essentially, it is a canary in the mine for other reefs worldwide.
And because this reef is very old and essentially unaltered—unlike those found in many other parts of the world’s oceans—it provides a reference point for understanding the original natural biodiversity of a coral reef; as well as its role in providing goods and services, such as fisheries and carbon cycling. It also helps us reconstruct past ocean environments to decipher modern climate change. Open waters cover more than 95 percent of the known GMR, of which less than 5 percent have been investigated through modern research expeditions. It’s very likely there are more reef structures across different depths waiting to be explored.
Future corals favor generalists
Most reef-building corals contain photosynthetic cells, called zooxanthellae, that live in their tissues. The corals and these special cells have a mutualistic, symbiotic relationship. The corals provide the zooxanthellae with a protected environment and compounds they need for photosynthesis. In return, the zooxanthellae produce oxygen and help the corals to remove wastes. Most importantly, zooxanthellae supply the corals with amino acids, glucose and glycerol, which are the products of photosynthesis. Corals use these products to make carbohydrates, fats and proteins; and to produce calcium carbonate, the building material of reefs. As much as 90 percent of the organic material photosynthetically produced by the zooxanthellae is transferred to the tissues of the host corals. This is the driving force behind the growth and productivity of coral reefs.
It’s important to study the biology of corals and their symbionts so we can predict how they will respond to future environmental changes, especially ocean warming. Not all corals and symbionts will respond in the same way. The world’s oceans contain thousands of species of corals, each with their own unique attributes. And, until recently, no one really appreciated the vast diversity of symbiont species and their importance to coral survival.
Scientists previously lumped all the symbionts into a few broad groups. But over the past several years, they’ve been able to identify individual species. They learned that some are specialists—meaning they can only associate with one or a few species of coral hosts; whereas others are generalists—meaning they can align with many species of coral hosts. In addition, the scientists found that some corals, especially from the Caribbean, rely on specialist symbionts; whereas corals from the Indo-Pacific associate with generalists. The lack of flexibility among Caribbean corals may make them more sensitive to environmental changes, while Indo-Pacific corals with more flexible partnerships may withstand greater ones.
Several host-generalist symbiont species in the Indo-Pacific region were formally described in the May 1, 2023, issue of the Journal of Phycology. Researchers collected samples of corals from across the Indo-Pacific, including the reefs of New Caledonia, Palau, the Phoenix Islands, Tanzania’s Zanzibar, Thailand and the Great Barrier Reef of Australia. Next, they extracted the symbiotic algae from these samples and sequenced their DNA. They then identified and described five species of symbionts that can associate with a variety of host coral species.
The symbiont species that the team described are important to reef ecosystems because of their ecological dominance and their importance to so many coral species over huge geographic areas. It’s possible that these thermally tolerant generalists may come to dominate coral communities as the planet’s oceans warm and more sensitive symbionts die out. Recognizing them enables more intensive research into their ecology.
Current corals need clear water
But what’s going on far below in the water isn’t where the only news about coral reefs resides. What’s happening above the ocean surface is also getting headlines.
Coral bleaching occurs when environmental conditions, such as rising ocean temperatures, cause the relationship between the algae and the coral animals to break down, resulting in a white, or bleached, colony. While corals can recover, bleaching may result in coral mortality, depending on the intensity and duration of the stress. Coral bleaching not only affects the corals themselves, but also entire ecosystems of organisms—from invertebrates, such as sea urchins and spiny lobsters, to vertebrates, such as fish and sea turtles.
To better understand coral bleaching, scientists looked at the role sunlight plays in the symbiotic relationship between corals and their algae. They found that underwater light intensity plays a critical role in the energy expended by the algae to maintain photosynthetic activity, and the maintenance of water optical quality in coral reefs is fundamental to protect coral biodiversity and to prevent reef degradation.
Publishing their findings in the journal Scientific Reports, scientists say this is hardly a revelation. Science has long shown that sunlight is the major source of energy for virtually all biochemical reactions that sustain life on Earth. However, sunlight’s impact on corals had not yet been fully understood.
To unravel the puzzle, researchers grew corals in an aquarium—simulating gradations of depth and sunlight—to develop a mathematical model that depicts the association between the depth-dependent variation in photosynthetic energy and gradients of coral species diversity.
They then tested the model on existing published data, comparing reefs with contrasting biodiversity patterns and water clarity in hot spots of marine biodiversity across the globe. The new model explained 64 to 95 percent of the depth-related variation in coral species richness, indicating that changes in exposure to sunlight is a driving force. Therefore, highly productive submarine environments, with plentiful access to sunlight, are a vital safeguard against the risk of coral extinctions from environmental changes.
These results offer a new tactic for reef conservation: preserving the clarity of the water. It’s as vital as limiting ocean acidification, pollution mitigation and reducing the sedimentation associated with human development.
Calcium carbonate comeliness (or: More than surface beauty)
The deep-sea submarine Alvin and its human explorers revealed even more of the astounding beauty and complexity of the biological and volcanic processes that make the Galapagos Islands so unique. Continually learning about what’s going on below—and above—the surface makes our appreciation for such a one-of-a-kind landscape go even deeper.
Here’s to finding your true places and natural habitats,