Coral reefs—those things that shape some of surfing’s most previous platforms—are in as existential a crisis as ever, perhaps with no thanks in particular to us humanoids. Yada, yada, yada, the metamessage the environmentalists take redundant care in delivering. But that’s a dour note for another entry into this vast compendium of nautical intrigue.
Today, a positive spin whirs across our desktops: Not all coral reefs the world over are doomed to succumb to the pesky rash of marine heat waves that just doesn’t seem to abate. Thanks to hidden ocean currents, select reef habitats, such as a nameless one in the Andaman Sea in the northeastern Indian Ocean, get regular-enough infusions of cool, clear water when and where climate conditions dictate.
At least that’s what decades-long study by researchers at the University of Bremen’s Center for Marine Environmental Studies (MARUM) and the Deutsche Forschungsgemeinschaft (DFG) in collaboration with Thai marine scientists found and published in the journal Scientific Reports.
The researchers measured conditions over time while using forensic evidence entombed within coral skeletons to trace a wider story of the reef’s trials and tribulations. Brief marine-biology lesson, for no one in particular: Corals exist on a foundational level due to calcium carbonate deposits. Minerals beget life, too—sort of. As corals grow, and as calcium deposits build, they trap chemicals, or at least chemical information about the aqueous solution in which they dwell.
The researchers employed a strontium-to-calcium (Sr/Ca) ratio to chart subsurface water temperatures while also tracing the corals’ nutrition using carbon-isotope (variations of a chemical element) ratios. Plainly, the study found that a reef’s cooling (and health) depends on subsurface ocean currents, which is probably no surprise to anyone who’s plunged a few feet below the surface of even a swimming pool.
But things are a little more complex in the deep blue sea, where internal waves and thermocline changes take place with nuance. Different climate cycles—see the El Niño-Southern Oscillation (ENSO) and the Indian Ocean Dipole (IOD), where this reef is concerned—have bearings upon wind, ocean circulation, and the depth of the thermocline. All of the aforementioned, naturally, affect a reef’s temperatures.
The study’s most significant finding relative to today’s concerns is that the reef in question showed its most intensive natural cooling cycle during the “extraordinary” El Niño event of 1997 and 1998, when the IOD came very strongly into play.
The thermocline was found to be abnormally shallow at the time, and lent a cool flood of relief to the beleaguered reef. Elsewhere, that El Niño led to some of the most prolific cases of coral-bleaching on record.
Another quick marine-biology lesson: Coral reefs build on calcium-carbonate deposits, but the living parts—and the tiny algae that live within the corals’ tissues—photosynthesize in order that corals might flourish and grow. When water gets too warm, that relationship fails, and the corals kick the algae out of home and hearth. This is what is colloquially known as “bleaching.”
The records developed by the research suggest that when the Andaman reef in question becomes stressed, its corals generally respond by engaging in heterotrophy, or catching food particles from the surrounding water, a strategy corals resort to when they lose their primary energy source (from algae).
During the 1998 El Niño, however, the corals’ heterotrophic activity did not increase, and the researchers concluded that extraordinary cooling must have led the corals to keep their little busy-bee algae within and resumed their normal operations, despite the marine heatwave.
While this is an encouraging finding for coral reefs the world round, the researchers’ findings also stress that such naturally-cooled reefs don’t necessarily have permanence. As climate conditions change a reef that survives one heatwave might not necessarily ride out the next.
Still, cool water continues to circulate, and studying those shifts and their impacts may play bigly into marine biologists’ understanding of which reefs are likely to withstand impact ahead of marine heatwaves.
That knowledge may inform protection and conservation efforts, but all in all, lest we need reminding: It just goes to show that mother ocean takes care of herself and her own—and that she needs us far less than we oh-so-gravely need her.
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