Shedd Aquarium postdoctoral researcher Shayle Matsuda spotted the white as she peered over the edge of the research vessel Coral Reef II, sailing in the Florida Keys.
Matsuda and a group of researchers from the aquarium and other institutions witnessed firsthand how coral reefs that were healthy and vibrant just two months ago were rapidly graying when they returned to the Sunshine State for their most recent trip.
An unprecedented rise in ocean temperatures off the coast of Florida in early summer made headlines when countless dead fish washed ashore. But according to Shedd’s research in collaboration with the University of Miami, the Palm Beach Zoo and the University of Southern California, the effect spread much more widely than was initially apparent.
Shedd research biologist Ross Cunning said 90 percent to 95 percent of the corals they surveyed for a week at 76 sites in the Keys and Dry Tortugas showed signs of excessive bleaching. Some coral species, such as endangered branched corals such as staghorn and elkhorn, were almost entirely dead.
“We pull up to the reef on the boat, and before we even got into the water you could see the stark, bright white color of these bleached corals,” Cunning said. “This was no wonder. “So we knew how severe these effects were before we even got into the water.”
The bleaching got worse as the researchers moved south. Along the dry Tortugas, they dived to depths of 60 feet, hoping to have a better chance of encountering survivors. But they couldn’t find a single live staghorn coral.
Researchers call this “the worst coral bleaching event Florida has ever experienced.”
Corals bleach when the waters are too warm because the tiny algae that live in their tissues and provide them with essential nutrients through photosynthesis cannot survive in the high temperatures. Losing their primary food source causes corals to lose color and bleach, leaving them vulnerable to starvation and disease.
“Bleaching is not inherently bad as a stress response,” Matsuda said. The researchers explained that corals expel algae in response to seasonal temperature increases, so even if a coral bleaches, it doesn’t necessarily mean it’s dead.
If temperatures retreat over time, this could alleviate heat stress on corals and allow them to regain lost symbiotic algae as well as food sources and color.
However, it becomes a problem if the bleaching takes several weeks longer and the corals continue to starve. “Then they’ll die,” Cunning said.
Corals serve as habitat for many other animals and fish. A quarter of all marine life They spend a significant portion of their lives on coral reefs, according to the U.S. Environmental Protection Agency. One of the most biodiverse ecosystems on the planet, coral reefs are often referred to as the rainforests of the sea, and corals are their building blocks.
“It would be like a forest without trees. You have no trees, you have no forest; All animals living in the forest have no habitat. The same thing happens with coral reefs, Cunning said. “If you don’t have corals, you don’t have coral reefs. As corals die, their skeletons will begin to break down over a long period of time, similar to how dead trees eventually fall over. “And if you lose that structure, you lose that habitat, and that’s when we’ll start to see the loss of all these other species that no longer have habitat.”
Shedd has been studying heat tolerance in corals for several years and has been helping international conservation efforts for endangered Caribbean corals for more than a decade.
In 2019, Tribune accompanied Cunning and other Shedd researchers on a trip to the Bahamas, where they placed live coral fragments in open ocean underwater nurseries to identify the toughest, most heat-tolerant coral species that were more likely to perform better and survive. in warming oceans.
That mission has become much more important now than it was four years ago, Cunning said, “because what’s happening in Florida this summer is going to happen more and more frequently and more intensely.”
At the Shedd, aquarists grow and propagate corals (most of their collections come from the Pacific, as Caribbean corals are banned in the aquarium trade). Cunning and Matsuda use it to complement field research with experimental fieldwork.
Behind the scenes of a busy aquarium on a recent day, Cunning held up a dead staghorn coral, whose rough surface was pure white and covered in tiny knots that might have been invaded by coral tissue that resembled polyps or tiny tentacles. The specimen was still alive.
“We had to look at a lot of these very closely when we were in the field in September,” he said, scanning the dead corals in his hands. “Many appeared to be a bright, clean white; We would look closely at some of them and we could detect a piece of the remaining tissue in those columns. “But others, we looked very closely and couldn’t see anything, indicating that either there was too little living tissue left for us to see with our eyes, or they had recently died.”
Elkhorn and staghorn corals are two of the most important reef-building species in Florida and the Caribbean and thus have long been the focus of many conservation efforts. Cunning said it was especially devastating for him to see most of the coral off Florida’s coast die over the summer.
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“On one hand, we all knew this was coming. “It wasn’t really a surprise because we’ve known for a very long time what warm water temperatures do to corals,” Cunning said. “And we’ve known for a very long time that we’re causing our planet and our oceans to warm. So it’s not a surprise in that sense, but it was still shocking to witness and heartbreaking to see. ”
For researchers, the mass bleaching and death of corals in Florida represents a harbinger or indicator of what is to come for coral reefs in warming oceans around the world.
“There are no reefs anywhere in the world that are immune to or protected from the effects of global climate change,” Cunning said. “We cannot find a way out of this problem for coral reefs or the rest of our planet. We must stop emissions and the further warming of our planet. And this needs to happen now and on a global scale. “So far, we have not seen the level of action we need against climate change to ensure the survival of reefs and the rest of our planet.”