Nav: Home

Breakthrough in live coral imaging

March 06, 2017

Corals are calcifying animals and are the prime architects of the most diverse marine ecosystem, the coral reefs. The coral animal harbors tiny microalgae as symbionts in its tissue, where they fix CO2 via photosynthesis and provide the animal host with organic carbon for its respiration. In turn, the microalgae obtain shelter and nutrients in the coral tissue, which extends over a complex calcium carbonate skeleton deposited by the animal host.

The coral host takes several measures to optimize light harvesting of its symbionts, while avoiding excess light exposure. This includes tissue contraction and relaxation as well as synthesis of coral host pigments, including brightly fluorescent protein complexes similar to the well-known green fluorescent proteins that are widely used as cell markers in the life sciences.

Direct observation of living corals is not easy and has relied on bright field imaging and epifluorescence microscopy with limited depth and areal resolution due to the opaque coral tissue, which is composed of different cell layers, as well as diffuse backscatter from the underlying coral skeleton. The use of visible light for such observations can also influence the corals, e.g. by stimulating photosynthesis or by exposure to potentially harmful UV and blue light.

An international team of scientists headed by professor Michael Kühl at the Department of Biology, University of Copenhagen has now surpassed such limitations in observing the tissue organization of living corals by using optical coherence tomography.

Michael Kühl explains, "OCT is an optical ultrasound-like technology that is e.g. employed by doctors to monitor tissue damage in the eye. It involves the use of non-actinic near-infrared radiation that penetrates deeper into tissue than visible light and can reveal microscopic structures with different reflective properties. We used an OCT system that enabled rapid 3D scanning of a 1-2 cm2 area down to a tissue/skeleton depth of 1-3 mm at a spatial resolution of a few μm. This enabled fascinating insights to the internal and external tissue-organization over the skeleton of living corals."

It was possible to identify different tissue layers and quantify their plasticity upon changes in light exposure on living corals. Corals rapidly contracted their tissue under high light stress, making it more reflective thereby protecting their symbionts against excess light. OCT also enabled the quantification of fluorescent host pigments organized in granules that also made the tissue more reflective especially after contraction.

In the dark, corals expand their tissues to gain better access to oxygen, and OCT showed that the tissue surface area of corals can be doubled at nighttime. The surface area of corals exposed to seawater and incident light is thus very dynamic, and OCT can now quantify such changes. This can have important implications for the measurements of coral metabolic rates, which typically are normalized to the surface area of the coral skeleton after the tissue has been removed - assuming that such area measurements are representative of the coral tissue surface area. The OCT results indicate that this assumption needs revision.

It was also possible to monitor the production of coral mucus on the tissue surface, which is an important component of coral life as mucus harbors beneficial microorganisms and also traps particles for feeding or self-cleaning purposes. Enhanced mucus production is also a signature of stressed corals, e.g. upon onset of coral bleaching. Furthermore, corals can expand special defensive tissue structures such as mesenterial filaments upon mechanical stress, and OCT could also visualize such dynamic responses.

Michael Kühl summarizes: "OCT is a powerful technique for studying the dynamic structure of living corals and their behavioral response to environmental stress. It now enables many novel applications in coral science as well as in other areas of marine biology. Our study also illustrates the importance of interdisciplinary approaches in science. Who would have thought that a technique used in the eye clinic would be useful for coral research?"
-end-


Faculty of Science - University of Copenhagen

Related Biology Articles:

Experimental Biology press materials available now
Though the Experimental Biology (EB) 2020 meeting was canceled in response to the COVID-19 outbreak, EB research abstracts are being published in the April 2020 issue of The FASEB Journal.
Structural biology: Special delivery
Bulky globular proteins require specialized transport systems for insertion into membranes.
Cell biology: All in a flash!
Scientists of Ludwig-Maximilians-Universitaet (LMU) in Munich have developed a tool to eliminate essential proteins from cells with a flash of light.
A biology boost
Assistance during the first years of a biology major leads to higher retention of first-generation students.
Cell biology: Compartments and complexity
Ludwig-Maximilians-Universitaet (LMU) in Munich biologists have taken a closer look at the subcellular distribution of proteins and metabolic intermediates in a model plant.
Cell biology: The complexity of division by two
Ludwig-Maximilians-Universitaet (LMU) in Munich researchers have identified a novel protein that plays a crucial role in the formation of the mitotic spindle, which is essential for correct segregation of a full set of chromosomes to each daughter cell during cell division.
Cell biology: Dynamics of microtubules
Filamentous polymers called microtubules play vital roles in chromosome segregation and molecular transport.
The biology of color
Scientists are on a threshold of a new era of color science with regard to animals, according to a comprehensive review of the field by a multidisciplinary team of researchers led by professor Tim Caro at UC Davis.
Kinky biology
How and why proteins fold is a problem that has implications for protein design and therapeutics.
A new tool to decipher evolutionary biology
A new bioinformatics tool to compare genome data has been developed by teams from the Max F.
More Biology News and Biology 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

Making Amends
What makes a true apology? What does it mean to make amends for past mistakes? This hour, TED speakers explore how repairing the wrongs of the past is the first step toward healing for the future. Guests include historian and preservationist Brent Leggs, law professor Martha Minow, librarian Dawn Wacek, and playwright V (formerly Eve Ensler).
Now Playing: Science for the People

#566 Is Your Gut Leaking?
This week we're busting the human gut wide open with Dr. Alessio Fasano from the Center for Celiac Research and Treatment at Massachusetts General Hospital. Join host Anika Hazra for our discussion separating fact from fiction on the controversial topic of leaky gut syndrome. We cover everything from what causes a leaky gut to interpreting the results of a gut microbiome test! Related links: Center for Celiac Research and Treatment website and their YouTube channel
Now Playing: Radiolab

The Flag and the Fury
How do you actually make change in the world? For 126 years, Mississippi has had the Confederate battle flag on their state flag, and they were the last state in the nation where that emblem remained "officially" flying.  A few days ago, that flag came down. A few days before that, it coming down would have seemed impossible. We dive into the story behind this de-flagging: a journey involving a clash of histories, designs, families, and even cheerleading. This show is a collaboration with OSM Audio. Kiese Laymon's memoir Heavy is here. And the Hospitality Flag webpage is here.