Warming Oceans Mean Extinction for Reef-Building Corals, Study Finds
by AMNH on
Photos courtesy of James Reimer
New research led by scientists from the Museum and Harvey Mudd College (HMC), suggests that without a significant change in human-caused carbon emissions, reef-building corals will go extinct while softer corals and sea anemones persist.
The research team traced the evolution of corals, sea anemones, and their relatives through deep time and found that changes in ocean chemistry and temperature dramatically affected the group’s diversity and will likely continue to do so in the future.
“This study shows us how nature through evolution is able to adapt, survive and reinvent itself, so when hard corals are not able to survive, their soft-bodied relatives such as sea anemones will thrive instead,” said Estefanía Rodríguez, curator in the Museum’s Division of Invertebrate Zoology and a co-author on the study, published today in the journal Nature Ecology and Evolution. “The question is whether we will be able to adapt and reinvent ourselves once nature, as we currently know it, is not there anymore.”
New genomic analyses reported in the study show that corals, which together with sea anemones and other relatives make up a class of animals known as anthozoans, have been on the planet for 770 million years. That’s 250 million years before the earliest undisputed fossil evidence of their existence—and long enough to experience massive shifts in climate, fluctuations in ocean chemistry, and several mass extinctions.
The researchers examined how these past conditions impacted anthozoan diversity with a new molecular approach developed by Andrea Quattrini, formerly at HMC, now curator of corals at the Smithsonian’s National Museum of Natural History, Catherine McFadden, the Vivian and D. Kenneth Baker Professor of Biology at Harvey Mudd College, and Rodríguez. The method allowed the team to compare nearly 2,000 key regions of anthozoan genomes to discern the evolutionary relationships between species.
Hundreds of anthozoan specimens collected around the world and now stored in museum collections were included in their analysis. When this molecular data was aligned with fossil evidence of anthozoan history, it revealed how these diverse animals evolved over geologic time.
Over the Earth’s history, changes in acidity and ion concentrations have shifted the ocean’s chemical composition between two states, known as aragonite and calcite seas. These changes, as well as changes in ocean water temperature, appear to have played an important role in determining what kinds of skeletons corals were able to produce.
Stony corals —the type that build massive reefs that support complex marine ecosystems—take up minerals from the water to construct hard skeletons from a form of calcium carbonate known as aragonite. Other corals, such as sea fans and black corals, build their softer skeletons from protein or calcite (a less soluble form of calcium carbonate), whereas sea anemones have no skeleton at all.
The researchers found that reef-building corals emerged only when conditions favored the construction of their aragonite skeletons—periods of aragonite seas, when ocean temperatures were relatively cool. During periods of calcite seas, when carbon dioxide is more abundant in the atmosphere and oceans are more acidic, evolution favored anemones and corals that built their skeletons from protein or calcite.
It was the soft anthozoans that fared best after reef crises—times when up to 90 percent of reef-building organisms died off as oceans warmed and became more acidic.
“Unfortunately, although these softer bodied species may adapt better to climate change than the stony corals, they don’t form large reefs. So in the future, reefs may be replaced by different marine communities,” McFadden said. “This already appears to be happening in the Caribbean where stony corals are being replaced by ‘forests’ of sea fans. Although stony corals have recovered from past reef crises and re-diversified, those recoveries have taken millions of years. That's a long time to wait for coral reefs as we know them to reappear.”
Preserving the Dry Coral Collection – Transcript
[The Museum's video logo appears over blurred footage of a colorful coral reef, followed by the title of the video, "Preserving the Dry Coral Collection".]
[The footage of the coral reef comes into focus, and the word "CNIDARIANS" appears with the phonetic pronunciation written underneath it: "NAHY-DAIR-EE-UHNS". We then see the first speaker on camera.]
ESTEFANíA RODRíGUEZ (Associate Curator, Division of Invertebrate Zoology, American Museum of Natural History):
Corals are Cnidarians. Cnidarians is a group of animals, around 10,000 species more or less, relatively simple, but very diverse, with many, many forms, including jellyfish, corals, anemones.
[As she says each of the forms of cnidarians, footage of that animal appears on screen.]
RODRíGUEZ: Stony corals are the corals that everybody knows.
[A large stony coral specimen with many curving branches sits in front of a black background. The words "stony coral" appears at the bottom of the screen with an arrow pointing towards the specimen.]
RODRíGUEZ: They are colonies of very little polyps. Basically sacks with tentacles that live in the sea floor,
[A close-up photo of pink/orange polyps with translucent tentacles appears on the screen with the words "CORAL POLYPS" and arrows pointing from the word to various polyps in the picture underneath.]
RODRíGUEZ: and they have the ability of producing an exoskeleton.
[Footage of live coral polyps visible on large pieces of flat coral in a reef.]
RODRíGUEZ: Like that, they produce the coral reefs that everybody knows and that are very, very important because they sustain a lot of other animals.
[An underwater camera drifts slowly across a colorful coral reef with many specimens in shades of greens and purples.]
RODRíGUEZ: They are the base for the whole community and they actually make deserts into very biodiverse coral reefs.
[Three consecutive shots of fish of many shapes and colors swimming amongst corals in different reefs around the world.]
CHRISTINE JOHNSON(Curatorial Association, Division of Invertebrate Zoology, American Museum of Natural History): In our coral collection here at the American Museum of Natural History, we have about a little over 4,000 specimens from all over the world. The collection dates back to about 1873.
[Three consecutive shots of Christine Johnson opening specimen drawers from various cabinets around the room, followed by a tilting shot of the inside of a specimen cabinet with many pieces of dry coral.]
JOHNSON: Some of these collections were donated by amateur collectors or some researchers, or they were considered by-catch. So, people would go out on expeditions for other things, and would bring back pieces of coral.
[Archival black-and-white footage of a woman swimming near a coral reef]
JOHNSON: And then there was an expedition to bring back a reef and to replicate a reef within the museum.
[Archival black and white footage of scientists collecting coral specimens in the wild and then assembling a display of coral at the Museum]
JOHNSON: And you can see that in the Hall of Ocean Life. It's a spectacular display.
[Footage of the Museum's coral reef diorama in the Milstein Hall of Ocean Life, followed by dry coral specimens on a cart in a lab setting.]
JOHNSON: But then we have specimens that are for researcher use only.
RODRíGUEZ: The collection of dry corals at the AMNH is important because it's old. That means that we can travel in time and see how the oceans were 200 years ago.
[Footage of a modern-day coral reef with fish swimming above fades into a 200-year old woodblock print of life on the sea floor.]
Nowadays, as people may be aware, coral is becoming increasingly endangered.
We decided that we really needed to put this effort into rehousing the coral, so that it's available to the outside world.
[One long shot of coral specimens arranged in their storage cabinets, with labels indicating that they are protected species.]
REZES: (Coral Rehousing Project Intern, Division of Invertebrate Zoology, American Museum of Natural History):
So we are currently six months in to our ongoing three-year project to clean, document and photograph the entirety of the dry coral collection at AMNH.
[Quick shots of someone cleaning a coral specimen, cleaning a specimen's label, and photographing a specimen.]
REZES:The way that we clean the coral is with a vacuum and a soft brush, right now we're using watercolor brushes. Who knew, very effective.
[A woman carefully holds a small vacuum hose up to a coral specimen while brushing dust off of the specimen into the vacuum.]
REZES:After we're all done cleaning, we take the time to photograph all of the specimens with all of their original labels from the donor.
[Emily arranges a specimen and its labels for photography and takes a picture.]
REZES:And this is because they can be some of the most detailed sources of locality information, and the date it was collected and the collector and things like that.
[A single specimen and its original label lie against a gray background. As Emily lists the type of information given by the label, that part of the label is highlighted.]
REZES:Most of the stuff that I've worked with before is an artwork that somebody has crafted in some way, whereas here, it was once living and it was grown and nobody has shaped it into this form.
[Three consecutive shots of coral specimens highlight the unique shapes stony corals form as they grow.]
REZES:My favorite species that I've worked with so far is Acropora Spicifera.
[A photograph of a large Acropora Spicfera specimen on a black background appears. The words "ACROPORA SPICIFERA" appear in the corner with an arrow pointing to the specimen.]
REZES:It's almost like lace, and if you get really close it kind of looks like a forest.
[Details of the specimen shown in the previous photograph]
One of my most favorite pieces is this single piece of black coral. This piece is just so beautiful and sleek and elegant.
[A slow tilting shot along the length of a piece of long, thin, black coral. The words "BLACK CORAL" appear in the bottom corner with an arrow pointing to the specimen.]
Corals are very beautiful, so I don't think I have a favorite one. Many of the pieces are amazing.
[A close-up, detailed shot of a stony coral specimen starts out blurred and comes into sharp focus.
By researchers coming here, carbon-dating the coral, and also looking at how environmental conditions have affected the coral, this will absolutely help us understand the fate of corals and how to protect corals going forward in the future.
[A shot of stony coral specimens in storage cabinets fades into footage of a living coral reef.]
Today, about 1,300 species of stony coral inhabit the ocean, favored by aragonite sea conditions. But rising levels of carbon dioxide in the atmosphere are warming and acidifying the waters, making them less hospitable for these and other organisms whose shells and skeletons are made from aragonite. The scientists say that the loss of reef-building corals will have devastating consequences for communities who depend on reefs and the rich, complex ecosystems they support for fishing, shoreline protection, and tourism.
“Aragonite is expected to dissolve under ocean acidification,” Quattrini said. “As our seas are becoming more acidic and warmer, it’s likely that the skeletons of corals will dissolve or not be able to grow. The best way to protect them is to curb our carbon emissions.”