Moses and the Israelites crossing the Red Sea. Image by Providence Lithograph Co., (1907). Source: Wikipedia
When the ancient Hebrews (apocryphally) crossed the Red Sea, with 600 chariots at their heels, they likely transited the Gulf of Aqaba or its sister, the Gulf of Suez.[1] However, even if they survived descents to average seabed depths of 2,624 ft (800 m) and 131 feet (40 m) respectively, and evaded the spears of their pursuers, the passage would have presented a challenge more daunting than either: coral.
Most images depict a level, sand-lined seabed under a few fathoms of water but in fact, for refugee and charioteer alike, the most immediate threat would have been the calcified spines of razor-sharp coral on the steep, irregular reefs lining both waterways. For any who made it before the waters crashed back down, triage for lacerations would have come before milk and honey.
Thousands of years later, it is the world’s reefs that require first aid. Half the planet’s coral is estimated to have died since the 1950s. Going forward, up to 90% of the remainder may be doomed over the next 30 years. Coral appears headed for extinction.
Coral spawning, Flower Garden Banks, National Marine Sanctuaries (NMS), Aug. 2005.
Photo by G.P. Schmahl /National Oceanic and Atmospheric Administration (NOAA).
Source: Wikimedia Commons
Yet corals may be attempting to save themselves. In a modern-day exodus, corals are leaving their tropical ranges and fleeing northwards, into warming basins and coastlines formerly too cold for their sensitive polyps and symbiotic algae. Yet, while a few species have been clocked at a blistering 8.7 miles (14 km) per year, others are not so speedy, and reef building is a tedious business. Reefs of even the fastest-growing corals build out at only about 10 cm per year. Indeed, scientists estimate the Great Barrier reef (GBR) took about half a million years to form.
Besides, new reefs farther north won’t save those left behind. Coral migration is so slow, and global warming now so rapid, that most if not all the world’s reefs are doomed – without human intervention. Fortunately, there is hope at the site of the original Exodus. The same bright and teeming Red Sea reefs that Moses may have cursed as they gouged and sliced his sandals, are thriving almost as well as they did in his day.
Beds of Red Sea coral near Hurghada, Egypt, 2010. Photo by Kallerna. Source: Wikipedia
But how? And how can science leverage the answer to save suffering reefs elsewhere? Researchers and marine engineers are racing to find out, with only a few decades to work with until modern reefs are functionally dead.
Scientists’ options, however, are limited. The primary causes of reef degradation and death – global warming, marine acidification, and pollution – are still escalating. In the near term at least, humans can neither cool, nor alkalize, nor cleanse the oceans.
Happily, the answers provided by Red Sea coral may lie not in shifting their range or rehabilitating their habitat, but in the genes of the corals and their algal symbionts themselves. Noting that many Red Sea corals are managing warmer, more acidic surface water better than those elsewhere, some scientists are testing them for the specific genes that make them hardier than corals of the same species elsewhere. If such varieties could be identified, improved, accelerated, and, in a sort of polyp diaspora, sent far and wide to re-colonize the world’s reefs, then coral may yet have a future.
Symbiodinium symbiotic zooxanthellae microalgae, necessary to coral nutrition,
but expelled by coral under heat stress. Photo by Todd C. LaJeunesse (2018).
Source: Wikimedia Commons
This methodology is being applied successfully to other warming-challenged organisms: as we noted in Vietnam Varietals (Nov. 2021),the genetic properties of critical flora and fauna are being cataloged for favorable genetic traits that allow them to thrive in 21st-century conditions – warmer, colder, saltier, more acidic, more polluted – conditions better than their cousins. As for corals, of the 2,500 or so known species, about 800 are reef builders and, of these, some twenty climate-resilient species have been identified in the Red Sea so far.
But how did they get there? Why are there corals which can withstand temperatures more than 5˚C over mean temperature in their home waters?
The answer, it appears, is that these were not the original waters of all the corals living there. Some, like the Israelites themselves, made an exodus from far hotter and more inhospitable places, such as the Arabian Sea off the Horn of Africa, reproducing and starting new colonies. Some polyps had adapted well to heat stress, and scions of these colonies moved – over some twenty millennia – into the calm, pellucid, and cooler waters of the Red Sea.
Coral column in the Red Sea, Egypt. Photo by Erwin ‘Tauchteufel’ Cox / Pixabay
Their descendants still retain that inherited resistance to heat stress, making them excellent candidates to repopulate reefs laid waste by warming seas. “One degree above an area’s summertime maximum monthly mean sea surface temperature for a period of a week (generally given as Degree Heating Week, or DHW) can be enough for bleaching to occur,” explains The Independent. “But these [Red Sea] corals have been known to survive a seven-degree rise.”
It should be noted that parallel research is ongoing regarding the symbiotic algae that inhabit – and through photosynthesis both feed and tint – coral polyps. It is the expulsion of these algae under heat stress that causes the ‘bleaching’ effect seen in dying corals. But in fact, it is becoming clear that the corals themselves aren’t so much expelling these algae, but rather, “in the events [sic] of high water temperatures… the algae becomes stressed and may escape into the water column.” In some ways the search for heat-tolerant strains of coral is also an effort to locate or create heat-tolerant varieties of their symbiotic algae.
There are several approaches currently under investigation. Certain researchers are using simple breeding techniques – genetic manipulation done every day with plants – selecting for, or removing, specific traits. Once they find an appropriate candidate, to protect genetic diversity the super corals are crossbred with those already on the target reef. “During breeding, the heat-resistant corals have a small advantage over the others and reproduce more as temperatures are slowly raised, meaning the entire population gradually becomes more heat-resilient,” the Independent explains. This accelerates a process that, without intervention, would require many millennia. With only a few decades before Earth’s reefs are expected to be effectively dead, any hastening of the process is critical.
Photo by Anirudh / Unsplash
Other scientists – less patient, perhaps, or more desperate – aren’t waiting for natural processes: they are reengineering corals to breed varieties with climate resilient characteristics. Either way, it’s a tedious and tricky business. As one coral scientist noted, “the Great Barrier Reef is the size of Italy — it would be impossible to repopulate it artificially.”
But human reef-reforming efforts are even trickier than that. Just this year, a team of Israeli scientists found that a particular species of branch coral, a “common symbiotic reef-building coral Stylophora pistillata from the Gulf of Aqaba,” exhibited excellent resistance to heat stress, with high tolerance and resilience up to 34.5˚C, offering “real hope for the preservation of at least one major coral reef ecosystem for future generations.”
With a range that “extends from Madagascar, East Africa… through the Indian Ocean to northern Australia, Indonesia, the Philippines, New Guinea, Japan and many island groups in the western and central Pacific Ocean,” this species appears perfectly positioned to repopulate many stagnant reefs.
However, there are other forces at work on reefs besides warming and acidification: fishing, dredging, and plain old pollution also take a toll. Subsequent studies of Red Sea stylophora pistillata found that warmer temperatures render that coral more susceptible to degradation from copper (Cu), “a common marine pollutant of coastal environments,” which suppresses coral’s ability to form skeletons.
When Cu pollution is combined with higher water-acidity levels, yet another study found, the damage is immediate and devastating. As a candidate species for reef reconstruction on far-flung reefs such as the Great Barrier Reef (GBR), the Belize Barrier (BBR), or the Apo Reef in the Philippines, to name a few? Very likely not.
Reef degradation has been moving rapidly and, to this point, the human response has been flaccid. But at least there is now significant research and several possible solutions for rebuilding – or at least re-seeding – global reefs, with specific coral strains that can resist global warming. The work is focused, notably, on the corals that must have lacerated the Israelites in their dash for freedom, the corals most closely associated with migration and diaspora: the super corals of the Red Sea.
[1] There is modern debate as to whether the body of water crossed in Exodus references the ‘Sea of Reeds,’ possibly a now -defunct lake, rather than either of the Red Sea Gulfs.