Nav: Home

What are the mechanisms of zooxanthella expulsion from coral?

December 29, 2014

Coral bleaching, which often results in the mass mortality of corals and in the collapse of coral reef ecosystems, has become an important issue around the world, with the number of coral reefs decreasing annually. Associate Professor Kazuhiko Koike and Ms. Lisa Fujise of the Graduate School of Biosphere Science at Hiroshima University and their collaborators have proposed mechanisms that might cause coral bleaching and damage. This research group demonstrated that corals more actively digest and expel damaged symbiotic zooxanthellae under conditions of thermal stress, and that this is likely to be a mechanism that helps corals to cope with environmental change. On the other hand, if the stressful conditions prevail, accumulation of the damaged symbiotic zooxanthellae may not maintain the expulsion, which will gradually accumulate in coral tissues. These researchers consider that this loss of zooxanthellae and the accumulation of damaged cells results in coral bleaching. These results were published as an article in PLOS ONE entitled "Moderate thermal stress causes active and immediate expulsion of photosynthetically damaged zooxanthellae (Symbiodinium) from corals" DOI: 10.1371/journal.pone.0114321.

The symbiosis between corals and zooxanthellae (dinoflagellate genus Symbiodinium) form the foundation of coral reef biology. The aforementioned research group demonstrated that the expulsion of zooxanthellae at 27°C (non-thermal stress conditions) is part of a regulatory mechanism that maintains zooxanthellal density and a stable carbon concentration with expulsion of digested or normal forms of symbionts. However, at 30°C (moderate thermal stress), Symbiodinium were damaged, and corals selectively digested the damaged cells or immediately expelled them without digestion by exocytosis, which is most likely to reflect an adaptive mechanism in response to moderate thermal stress to avoid the accumulation of damaged cells. However, under thermal stress, the accumulation of damaged cells may exceed the increased rate of expulsion of digested zooxanthella. More photosynthetically damaged zooxanthellae were observed upon prolonged exposure to thermal stress, and were released by corals without digestion, therefore preventing their accumulation. This response may be an adaptive strategy to moderate stress to ensure survival, but the accumulation of damaged Symbiodinium, which causes subsequent coral deterioration, may occur when this response cannot cope with the magnitude or duration of environmental stress, and this might be a possible mechanism underlying coral bleaching during prolonged moderate thermal stress.
-end-


Hiroshima University

Related Corals Articles:

How climate killed corals
A squad of climate-related factors is responsible for the massive Australian coral bleaching event of 2016.
Iron deficiency in corals?
When iron is limited, the microalgae that live within coral cells change how they take in other trace metals, which could have cascading effects on vital biological functions and perhaps exacerbate the effects of climate change on corals.
3D-printed corals could improve bioenergy and help coral reefs
Researchers have designed bionic 3D-printed corals that could help energy production and coral reef research.
Soft corals near Virgin Islands recover from hurricanes, but stony corals declining
Soft corals at three sites in the US Virgin Islands were able to recover from the destructive effects of nearly back-to-back Category 5 storms in 2017, but research by a UB marine ecologist puts that seemingly good news in the context of an ecosystem that is dramatically changing.
Stressed corals set up progeny for a better life
First evidence that animal DNA methylation patterns can be passed to the next generation.
Algae team rosters could help ID 'super corals'
U.S. and Australian researchers have found a potential tool for identifying stress-tolerant ''super corals.'' In experiments that simulated climate change stress, researchers found corals that best survived had symbiotic algae communities with similar features.
How do corals make the most of their symbiotic algae?
Corals depend on their symbiotic relationships with the algae that they host.
Gulf Coast corals face catastrophe
Gulf of Mexico coral reefs may only be saved by a dramatic reduction in greenhouse gas emissions beyond those called for in the Paris Agreement, according to Rice University-led research.
For some corals, meals can come with a side of microplastics
A new experiment by the University of Washington has found that some corals are more likely to eat microplastics when they are consuming other food, yet microplastics alone are undesirable.
New disease hits corals
The emergence of a new coral disease in Micronesian reefs, termed grey-patch disease, is reported in the open-access journal Microbiome.
More Corals News and Corals Current Events

Trending Science News

Current Coronavirus (COVID-19) News

Top Science Podcasts

We have hand picked the top science podcasts of 2020.
Now Playing: TED Radio Hour

Our Relationship With Water
We need water to live. But with rising seas and so many lacking clean water – water is in crisis and so are we. This hour, TED speakers explore ideas around restoring our relationship with water. Guests on the show include legal scholar Kelsey Leonard, artist LaToya Ruby Frazier, and community organizer Colette Pichon Battle.
Now Playing: Science for the People

#569 Facing Fear
What do you fear? I mean really fear? Well, ok, maybe right now that's tough. We're living in a new age and definition of fear. But what do we do about it? Eva Holland has faced her fears, including trauma and phobia. She lived to tell the tale and write a book: "Nerve: Adventures in the Science of Fear".
Now Playing: Radiolab

Uncounted
First things first: our very own Latif Nasser has an exciting new show on Netflix. He talks to Jad about the hidden forces of the world that connect us all. Then, with an eye on the upcoming election, we take a look back: at two pieces from More Perfect Season 3 about Constitutional amendments that determine who gets to vote. Former Radiolab producer Julia Longoria takes us to Washington, D.C. The capital is at the heart of our democracy, but it's not a state, and it wasn't until the 23rd Amendment that its people got the right to vote for president. But that still left DC without full representation in Congress; D.C. sends a "non-voting delegate" to the House. Julia profiles that delegate, Congresswoman Eleanor Holmes Norton, and her unique approach to fighting for power in a virtually powerless role. Second, Radiolab producer Sarah Qari looks at a current fight to lower the US voting age to 16 that harkens back to the fight for the 26th Amendment in the 1960s. Eighteen-year-olds at the time argued that if they were old enough to be drafted to fight in the War, they were old enough to have a voice in our democracy. But what about today, when even younger Americans are finding themselves at the center of national political debates? Does it mean we should lower the voting age even further? This episode was reported and produced by Julia Longoria and Sarah Qari. Check out Latif Nasser's new Netflix show Connected here. Support Radiolab today at Radiolab.org/donate.