For corals adapting to climate change, fat cells and flexibility are crucial
By Pam Frost Gorder
The future health of the world’s coral reefs and the animals that depend on them relies in part on the ability of one tiny symbiotic sea creature to get fat — and to be flexible about the type of algae it cooperates with.
In the first study of its kind, scientists At Ohio State have discovered that corals — tiny reef-forming animals that live symbiotically with algae — are better able to recover from yearly bouts of heat stress, called “bleaching,” when they keep large energy reserves — mostly as fat — socked away in their cells.
“We found that some coral are able to acclimatize to annual bleaching, while others actually become more susceptible to it over time,” said Andréa Grottoli, professor in the School of Earth Sciences. “We concluded that annual coral bleaching could cause a decline in coral diversity and an overall decline of coral reefs worldwide.”
The study, which appears in the journal Global Change Biology, indicates that some coral species will almost certainly decline with climate change, while others that exhibit large fat storage and flexibility in the types of algae they partner with will stand a better chance of enduring repeated rounds of stress as oceans get hotter.
“If we conserve reefs that contain coral species with these survival traits, then we’re hedging our bets that we might be able to preserve those reefs for an extra decade or two, buying them enough time to acclimatize to climate change,” Grottoli said.
Corals are essentially colorless; the colors we associate with them are actually the colors of algae living inside the corals’ cells. That’s why, when stressed corals dump algae from their cells, their bodies appear pale, or “bleached.”
Normally, bleaching is a rare event. But by 2025, Caribbean waters are expected to be hot enough that the coral living there will be stressed to the point of bleaching once a year. The rest of the tropics are expected to experience annual bleaching by 2050.
Bleached corals can recover by growing more algae or acquiring new algae once water temperatures return to normal. Corals can supplement their diet by eating plankton, but they get most of their energy by siphoning off sugars that algae produce in photosynthesis. Like humans, corals can store
excess energy as fat.
Previous studies followed coral through only one bleaching event, or through two events several years apart. This study tested what would happen if some common Caribbean corals bleached two years in a row.
Grottoli and her colleagues tested three corals from Puerto Morelos Reef National Park. Two years in a row, they plucked samples of finger coral, mustard hill coral and boulder coral from the ocean floor, and placed them in warm water tanks in an outdoor lab until the corals bleached. Both times, the researchers returned the corals to the ocean to let them recover.
The mustard hill coral kept low fat reserves and partnered with only one algal species. It recovered from the first round of bleaching but not the second. The boulder coral kept moderate fat reserves but partnered with six different algae and changed between dominant algal types following each bleaching. It recovered from both rounds of bleaching, though its growth slowed.
The real winner was the finger coral, which switched completely from one algal partner type to another over the course of the study and had the largest fat reserves. The finger coral was barely even affected by the second bleaching and maintained a healthy growth rate.
The bottom line: As some species adapt to climate change and others don’t, there will be less diversity in reefs, where all the sizes and shapes of coral provide specialized habitats for fish and other creatures. Interactions among hosts, symbionts, predators and prey would all change in a domino effect, Grottoli said. Reefs would be more vulnerable to storms and disease in general.
It sounds like a bleak picture.
“We’re actually a bit optimistic because we showed that there’s acclimation in a one-year window, that it’s possible,” she said. “In two of our three coral species, we have recovery in six weeks. The paths they took to recovery are different, but they both got there.”
Potential new target found in fight against E. coli
Scientists have identified a protein essential to the survival of E. coli bacteria and consider the protein a potential new target for antibiotics.
In the study, researchers confirmed that this protein, called MurJ, flips a fatty molecule from one side of a bacterial cell membrane to the other. If that molecule isn’t flipped, the cell cannot construct a critical layer that keeps pressurized contents of the cell contained. If those contents aren’t contained, the cell bursts.
E. coli is part of the gram-negative family of bacteria, characterized by an extra membrane, called the outer membrane, that reduces the chances for a drug to penetrate the cell to kill it. Inhibiting MurJ, however, would require getting past just one of the two membranes, meaning it could be an attractive new target for antibiotics in this age of resistant pathogens.
“We have proof of principle that MurJ is actually a valid target because we showed that if we stop it from working, the cells will die within 10 minutes — very quickly,” said Natividad Ruiz, assistant professor of microbiology at Ohio State and a co-lead author of the study.
“If you want to develop an antibiotic, it’s important to know a protein’s function. Defining the activity associated with MurJ is a big step toward possibly designing antibiotics that could target it.”
Ruiz co-led the study with Thomas Bernhardt, associate professor of microbiology and immunobiology at Harvard Medical School. The research was published in the July 11 issue of the journal Science.
Discovery expands search for Earth-like planets
A newly discovered planet in a binary star system located 3,000 light-years from Earth is expanding astronomers’ notions of where Earth-like — and potentially habitable — planets can form and how to find them.
At twice the mass of Earth, the planet orbits one of the stars in the binary system at almost exactly the same distance from which Earth orbits the sun. However, because the planet’s host star is much dimmer than the sun, the planet is much colder than the Earth — a little colder, in fact, than Jupiter’s icy moon Europa.
Four international research teams, led by professor Andrew Gould of Ohio State, published their discovery in the July 4 issue of Science.
The study provides the first evidence that terrestrial planets can form in orbits similar to Earth’s. Although this planet itself is too cold to be habitable, the same planet orbiting a sun-like star in such a binary system would be in the so-called “habitable zone” — the region where conditions might be right for life.
“This greatly expands potential locations to discover habitable planets in the future,” said Scott Gaudi, professor of astronomy at Ohio State. “Half the stars in the galaxy are in binary systems. We had no idea if Earth-like planets in Earth-like orbits could even form in these systems.”
Very rarely, the gravity of a star focuses the light from a more distant star and magnifies it like a lens. Even more rarely, the signature of a planet appears within that magnified light signal.
When the astronomers detected this new planet, they could document that it produced two separate signatures — the primary one, and a secondary one that had previously been only hypothesized to exist.