Corals know how to attract good company. New research finds that corals emit an enticing fluorescent green light that attracts the mobile microalgae, known as Symbiodinium, that are critical to the establishment of a healthy partnership.

The study led by researchers at Japan’s National Institute for Basic Biology and the ARC Centre of Excellence for Coral Reef Studies at James Cook University (Coral CoE) sheds new light on the mechanism that brings corals and Symbiodinium together, for example, following a bleaching episode.

“Most reef corals can not function without Symbiodinium,” said Shunichi Takahashi from the National Institute of Basic Biology.

“Following the back-to-back mass bleaching events, images of bleached white coral contrasted with healthy, vibrantly coloured coral were widespread. The key difference between the two is the abundance of Symbiodinum in the coral’s tissue. Without sufficient Symbiodinum, which provide corals with nutrients via photosynthesis, the coral will starve.”

“Thirty percent of corals receive their Symbiodinium from their parents, the other seventy percent, need a different mechanism” said co-author Professor Andrew Baird of Coral CoE.

But what brings the two organisms together? Corals are stationary creatures, however Symbiodinium can move freely through the water column.

The study reveals that corals have evolved a cunning ability to draw the Symbiodinium to them.

The researchers used the chalice coral, Echinophyllia aspera, to test whether the green fluorescent light emitted by corals under certain conditions can signal the Symbiodinium in the water column to move towards them: a process known as “positive phototaxis.”

“Our research identifies a novel biological signaling tool that underlies the success of a relationship essential for healthy coral reef ecosystems, ” said Prof Baird.

The paper “Green fluorescence from cnidarian hosts attracts symbiotic algae” is published in the journal Proceedings of the National Academy of Sciences.

CITATION
Aihara Y, Maruyama S, Baird AH, Iguchi A, Takahashi S, Minagawa J (2019) Green fluorescence from cnidarian hosts attracts symbiotic algae. Proceedings of the National Academy of Sciences 116 (6): 2118-2123

IMAGES
Link to images here. Please credit as marked.

CONTACT FOR INTERVIEW
Prof Andrew Baird
ARC Centre of Excellence for Coral Reef Studies at James Cook University
Phone: +61 (0) 400 289 770, +61 (0)7 4781 4857 (AEST/UTC +10)
Email: andrew.baird@jcu.edu.au

FOR FURTHER INFORMATION
Catherine Naum, Communications Manager
ARC Centre of Excellence for Coral Reef Studies
Townsville, QLD AUSTRALIA
P: +61 7 4781 5979, +61 (0)428 785 895 (AEST/UTC +10)
E: catherine.naum1@jcu.edu.au

A world-first study has revealed that “robust” reef-building corals are the only known organisms in the animal kingdom to make one of the “essential” amino acids, which may make them less susceptible than other corals to global warming.

Using advanced genomic techniques, a team of researchers led by Dr Hua (Emily) Ying of The Australian National University (ANU) and Prof David Miller of the ARC Centre of Excellence for Coral Reef Studies (Coral CoE) at James Cook University (JCU), have found that the group of corals classified as “robust,” which includes a number of the brain corals and mushroom corals, have a key physiological advantage over “complex” corals, including common branching corals such as the staghorn coral.

In a new paper published today in the prestigious journal Genome Biology, the researchers report that “robust” corals possess a unique capacity to generate an “essential” amino acid.

“Amino acids are the building blocks of life,” said lead author Dr Emily Ying of the ANU Research School of Biology.

“They are crucial, for example, in repairing tissue or growing new tissue. But, generating amino acids is energetically costly for animals, so they usually only generate 11 of the 20 required for life.”

“The remaining nine amino acids are called the ‘essential’ amino acids because they must be supplied by the animal’s diet. For corals, this includes tiny drifting animals known as ‘zooplankton.’”

But this is not the only form of sustenance for corals. Through a mutually-beneficial relationship with microalgae known as Symbiodinium, corals are supplied the energy needed to build their hard skeletons.

“Symbiodinium also supplies the coral with some of the ‘essential’ amino acids, making them less dependent on their diet than other animals,” said senior author Prof David Miller of Coral CoE at JCU.

For example, when global warming causes corals to bleach, they expel their resident Symbiodinium and are therefore suddenly fully dependent on their diet to meet this nutritional requirement.

“We now know that ‘robust’ corals can make at least one of the ‘essential’ amino acids without relying on Symbiodinium. This suggests that they may be more resilient, at least in the short term, to bleaching than the ‘complex’ corals such as the branching staghorns,” explained Prof Miller.

Until now, scientists had few clues about why some corals only host a specific Symbiodinium type and others are less particular.

“Our research also suggests that ‘robust’ corals are less choosey about which species of microalgae can take up residence in the coral’s tissue. The ability to host a broader range of Symbiodinium types could facilitate more rapid acclimation to higher temperatures,” said Prof Miller.

Note to editor:

• Since 1996, coral taxonomists have recognised the existence of two “superfamilies” of reef-building corals: “robust” and “complex.”

• Symbiodinium is a photosynthetic micro-alga that has a mutually beneficial relationship with reef-building corals – in exchange for the stable environment inside the coral cells, it supplies most of the energy needs of the host animal.

• Coral bleaching is the loss of Symbiodinium by coral hosts when they are stressed –especially by high temperatures. Symbiodinium cells depart from stressed corals, which makes the corals pale.

Citation: Ying, H, Cooke, I, Sprungala, S, Wang, W, Hayward, DC, Tang, Y, Huttley, G, Ball, EE, Forêt, S, Miller, DJ (2018) Comparative genomics reveals the distinct evolutionary trajectories of the robust and complex coral lineages. Genome Biology 19:175 DOI: 10.1186/s13059-018-1552-8

Visuals available here

CONTACTS

Prof David Miller
Coral CoE at JCU
Townsville, Queensland
E: david.miller@jcu.edu.au

Dr Hua Ying
ANU Research School of Biology
Canberra, ACT
E: Hua.Ying@anu.edu.au

More information

Catherine Naum, Communications Mgr
Coral CoE
T: +61 (7) 4781 6067
M: +61 (0) 428 785 895
E: catherine.naum1@jcu.edu.au

Check out Prof. Miller’s related talk from the 2018 “Coral Reef Futures” Symposium: