Breakthrough study shows coral reefs will transform but can persist, if carbon is curbed
University of Hawaii at Manoa
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Hawaiian coral reefs are teeming with life.
view moreCredit: Andre Seale.
In a breakthrough study published this week in Proceedings of the National Academy of Sciences, researchers in the Hawaiʻi Institute of Marine Biology (HIMB) at the University of Hawai‘i (UH) at Mānoa have shown that, contrary to most projections, coral reefs are not inevitably doomed, but have the potential to persist and adapt over time, if carbon emissions are curbed and local stressors are addressed. This work was conducted by the Toonen-Bowen “ToBo” Lab, with partners across UH Mānoa and The Ohio State University.
In an island-based laboratory adjacent to the coral reefs they study, HIMB researchers created 40 experimental systems known as “mesocosms,” which mimic the diversity and environment of a coral reef in the wild. The mesocosms included eight of the most common Hawaiian coral species, reef sand, rubble, and a menagerie of creatures which helped represent one of the most diverse ecosystems on the planet. For two years, the team exposed the mesocosms to different scenarios of higher temperature, higher acidity, or a combination of both ocean stressors to see how the reef communities would react to future climate scenarios.
“We included the eight most common coral species in Hawai‘i, which constitute about 95% of the coral cover on Hawaiian reefs, and many of the most common coral types across the Pacific and Indian Oceans,” explains HIMB post-doctoral researcher and lead author of the study, Christopher Jury. “By understanding how these species respond to climate change, we should have a better understanding of how Hawaiian reefs and other Indo-Pacific reefs will change over time, and how to better allocate resources as well as plan for the future.”
Reef structures form over time through a process known as “calcification” where individual coral organisms—or polyps—build their own skeletons by secreting a salt known as calcium carbonate, which becomes limestone. Coral reefs are naturally eroded by a variety of species, and if the balance between reef producers and reef eroders shifts, coral reefs could disappear, and the huge diversity of species which live on coral reefs would have nowhere to live.
As the ToBo lab research team controlled levels of temperature and acidity in the mesocosms, they measured the calcification responses of the eight species of coral, the reef communities, and the biodiversity of these systems. Their findings were entirely unexpected.
“These experimental reef communities persisted as new reef communities rather than collapsing,” shares Jury. “This was a very surprising result, since almost all projections of reef futures suggest that the corals should have almost entirely died, the reef communities should have experienced net carbonate dissolution, and reef biodiversity should have collapsed. None of those things happened in this study.”
Their results are unique, and so is the ToBo lab’s approach to how they study their subject.
“Rather than focusing on just one or two species in isolation, we included the entire complement of reef species from microbes, to algae, invertebrates, and fish, under realistic conditions they would experience in nature,” notes Rob Toonen, co-director of the UH Marine Biology Graduate Program, HIMB Professor and Ruth Gates Endowed Chair, and co-senior author of the study. “These more realistic mesocosm experiments help us to understand how coral reefs will change over time.”
These findings suggest that coral conservation in a changing world is possible, but urgent action is essential for these unique ecosystems to persist.
“Reefs are not inevitably doomed,” emphasizes Jury. “The recognition that coral reefs are not doomed if we take appropriate action on climate change and local stressors reinforces the need to accomplish these goals. Under potential future ocean warming and acidification, coral reef communities will change substantially, but are unlikely to collapse if global change is limited to Paris Climate Agreement targets and local stressors are adequately addressed.”
Coral reefs are among the most diverse ecosystems on the planet, and they support hundreds of millions of people around the world. As our planet rapidly changes in unprecedented ways, coral reefs are under severe threat due to ocean warming and acidification. This study shows that with effective and timely climate change mitigation measures in place, coral reefs will continue to change, but global reef collapse may still be avoidable.
Hawai‘i Institute of Marine Biology (HIMB) is located on Moku o Lo‘e, a storied islet in Kāne‘ohe Bay on the Hawaiian island of O‘ahu. HIMB’s unique location provides researchers with unparalleled, immediate access to their research subject. In this image, a research diver encounters Porites evermanni
Caption
A mesocosm system at the Hawai‘i Institute of Marine Biology enables researchers to carefully control and study the impact of ocean warming and acidification while preserving realistic conditions, like those on nearby reefs.
Credit
Mariana Rocha De Souza
Journal
Proceedings of the National Academy of Sciences
Method of Research
Experimental study
Subject of Research
Animals
Article Title
Experimental coral reef communities transform yet persist under mitigated future ocean warming and acidification
Deep-sea corals are home to previously unknown bacteria with extremely small genomes
Microbes lack ability to break down carbohydrates – species belong to new family of marine bacteria.
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The deep-sea coral Callogorgia delta is often found in the Gulf of Mexico near cold seeps. The pink-coloured brittle stars are probably useful for the corals. The photo was taken at a depth of 439 metres.
view moreCredit: ECOGIG consortium
A German-American research team led by Professor Iliana Baums from the Helmholtz Institute for Functional Marine Biodiversity at the University of Oldenburg (HIFMB) and Dr Samuel Vohsen from Lehigh University in the US has discovered two highly unusual bacterial species in the tissue of two deep-sea corals from the Gulf of Mexico. These previously unknown coral symbionts have an extremely reduced genome and lack the ability to obtain energy from carbohydrates, the team reports in an article published in the scientific journal Nature Communications. “These species are impressive examples of how few genes are needed for a functional organism,” says Baums, who co-authored the paper.
The research team studied several colonies of two soft coral species, Callogorgia delta and Callogorgia Americana, which are found in the Gulf of Mexico at depths ranging from 300 to 900 metres, where it is completely dark. The researchers discovered two previously unknown, closely related species from the mollicutes class of bacteria. Mollicutes often live as parasites either on or in the cells of plants, animals and humans, and in some cases cause diseases. On the basis of their genetic analyses, the researchers propose a new family called Oceanoplasmataceae, to which the two bacteria are to be assigned.
Further investigations revealed that the bacteria are the dominant symbionts of these corals and live in a gelatinous layer of tissue that forms part of their immune defence system and transports nutrients. One of the species (Oceanoplasma callogorgiae) contains only 359 genes which encode proteins for various metabolic functions. The other (Thalassoplasma callogorgiae) has 385 protein-coding genes. By comparison, the intestinal bacterium Escherichia coli contains more than 4,000 such genes, while humans have around 21,000 of them.
Amino acid is their only source of energy
The question of how the metabolism of the two newly discovered microbes can function with such a reduced genome remains a mystery to the researchers: “These bacteria don’t even carry genes for normal carbohydrate metabolism, in other words, for obtaining energy from carbohydrates – something that basically every living organism has,” Baums explains. According to the research to date, their only source of energy is the amino acid arginine, which is provided by the host coral. “But the breakdown of this amino acid provides only tiny amounts of energy. It is astonishing that the bacteria can survive on so little,” says Vohsen. The bacteria also obtain other essential nutrients from their host.
It remains unclear whether the microbes are purely parasites, or whether the corals benefit in some way from their symbionts. According to the scientists’ genetic analysis, the two bacterial species use various defence mechanisms called CRISPR/Cas systems to remove foreign DNA. These systems are also used in biotechnology to edit genes. The researchers hypothesise that these mechanisms may also be useful to the host corals, helping them to fend off pathogens. Another possibility is that the bacteria provide nitrogen to their host when they break down arginine.
For Baums, whose research focuses on both the ecology and evolution of corals, the symbionts offer an opportunity to gain further insights into the history of this diverse group of animals. “I always find it amazing that corals can colonise so many different habitats despite being very simple animals in terms of their genetic blueprint,” says the researcher. Symbionts are crucial for the ability of corals to adapt to different environmental conditions, she explains: “They provide metabolic functions that the corals themselves lack.” For example, tropical corals, which live in shallow, light-flooded waters, rely on photosynthetic algae to provide them with food and energy. Cold-water corals, many of which live in the dark and nutrient-poor deep sea, are thought to rely on bacteria to convert nutrients or obtain energy from chemical compounds.
Baums, an evolutionary ecologist and coral expert, conducts research at the Helmholtz Institute for Functional Marine Biodiversity at the University of Oldenburg (HIFMB) and holds a joint professorship at the University of Oldenburg and the Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research in Bremerhaven. In addition to Professor Baums and Dr Vohsen, scientists from the Max Planck Institute for Marine Microbiology in Bremen, Kiel University and Pennsylvania State University in the US were also involved in the current study.
This deep-sea community was discovered in 2016 at a depth of 624 metres in the Mississippi Canyon, Gulf of Mexico. The coral Callogorgia delta is accompanied by tubeworms and a clam.
Credit
ECOGIG Consortium
Journal
Nature Communications
Method of Research
Observational study
Subject of Research
Animals
Article Title
Discovery of deep-sea coral symbionts from a novel family of marine bacteria, Oceanoplasmataceae, with severely reduced genomes
Article Publication Date
4-Nov-2024
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