Coral larvae movement is paused in reaction to darkness
Researchers find a new light responding behavior that may affect where
corals live

Date:
November 4, 2020
Source:
National Institutes of Natural Sciences
Summary:
A new study shows that coral larvae swimming in seawater behave
in such a manner so as to temporarily stop swimming due to reduced
light, especially blue light. Researchers think that this behavior
may play a role in determining where corals settle.



FULL STORY ========================================================================== Light is essential for the growth of reef-building corals. This is
because corals grow by using the photosynthetic products of the algae
living inside their cells as a source of nutrients. Therefore, the light environment of coral habitats are important for their survival.


==========================================================================
A new study published in Scientific Reports shows that coral larvae
swimming in seawater behave in such a manner so as to temporarily stop
swimming due to reduced light, especially blue light. Researchers think
that this behavior may play a role in determining where corals settle.

Corals can only move freely during the larval stage of their lives. Larvae
that hatch from eggs are able to swim by moving the cilia on the surface
of their bodies. After that, when the larva settles on the seabed and transforms into a sedentary form (called a "polyp"), it becomes immobile.

How the corals, whose growth requires light, select a suitable light environment for survival is a mystery. To solve it, a research team led
by Dr.

Yusuke Sakai, Professor Naoto Ueno of the National Institute for Basic
Biology in Japan thoroughly observed the response of coral larvae to
light. They found that coral larvae temporarily stop swimming in response
to a decrease in light intensity and then subsequently resumed swimming
at their initial speed.

Corals mostly lay eggs once a year. "In collaboration with Andrew Negri, principal investigator at the Australian Institute of Marine Science,
and Professor Andrew Baird and his colleagues at James Cook University,
we have not only tested corals in Japan, but also in Australia's Great
Barrier Reef, where coral spawning occurs at a different time than
here. This was performed in order to repeat the experiment and thus
validate our findings " said Dr. Sakai.

The research team then conducted a detailed analysis of the wavelengths
of light that coral larvae react to. The Okazaki Large Spectrograph,
the world's largest spectroscopic irradiator at the National Institute
for Basic Biology, was used for this experiment. Experiments with coral
larvae exposed to various light wavelengths revealed that coral larvae
respond strongly to purple to blue light.

How does pausing behavior in response to light decay affect the
destination of coral larvae? To answer this question, researchers
conducted mathematical simulations; the results of which show that the
pause caused by the attenuation of light and the subsequent resumption
of swimming have the effect of resetting the swimming direction of the
larva once when it moves into a dark region and turning it in a random direction. As a result, it was suggested that it would lead to the
gathering of larvae in a bright space.

Dr. Sakai said "In cnidarians, including corals, the mechanism of light reception is largely unknown. We would like to clarify the molecular
mechanism of light reception in coral larvae, which do not have an eye structure." "In the future, it will be important to elucidate not only
this phenomenon but also the mysterious ecology of coral at the molecular
and cellular levels, such as the mechanism for controlling the spawning
time" Professor Naoto Ueno commented.


========================================================================== Story Source: Materials provided by
National_Institutes_of_Natural_Sciences. Note: Content may be edited
for style and length.


========================================================================== Journal Reference:
1. Yusuke Sakai, Kagayaki Kato, Hiroshi Koyama, Alyson Kuba, Hiroki
Takahashi, Toshihiko Fujimori, Masayuki Hatta, Andrew P. Negri,
Andrew H.

Baird, Naoto Ueno. A step-down photophobic response in coral larvae:
implications for the light-dependent distribution of the common
reef coral, Acropora tenuis. Scientific Reports, 2020; 10 (1) DOI:
10.1038/ s41598-020-74649-x ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2020/11/201104102158.htm

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