A team of coral researchers from QUT in Australia captured the effects global warming has on corals. A combination of a microscope, digital camera, and a smart tablet was used to record close-up.
Researchers Brett Lewis and Dr Luke Nothdurft placed solitary corals, Heliofungia actiniformis, into controlled aquaria, before heating the water up to simulate rising sea surface temperatures.
Their resulting videos, described in the peer-reviewed Coral Reefs, show the unhappy corals belching Symbiodinium, tiny algae cells that live within coral tissue and give corals their vibrant colours.
Mr Lewis said previous studied had shown H. actiniformis was one of the very few corals on the Great Barrier Reef considered to be relatively resilient to bleaching, even as neighbouring species suffered the full effects.
"Our observations suggest this resilience could be due to the rapid expulsion of the coral's algal symbionts during thermal stress, and could very well increase H. actiniformis's chance of survival during abnormally high sea temperatures."
During the experiments, the team raised the water temperature in a 10-litre aquarium system from 26oC to 32oC over 12 hours, where it remained for up to eight days.
While scientists have known for some time that coral bleaching occurs when the relationship between the coral and their Symbiodinium
breaks down as ocean temperatures rise, the QUT team's time-lapse videos show for the first time how this coral removes the algae.
"Our H. actiniformis used a pulsed inflation to expel Symbiodinium
over time (seen as greenish plumes in the video) – inflating their bodies to as much as 340 percent of their normal size before suddenly and violently contracting and ejecting Symbiodinium
through their oral openings over the four to to eight day duration of the experiments" Dr Nothdurft said.
Dr Nothdurft said reef-building corals and their algal Symbiodinium
had evolved to form a mutually-beneficial relationship.
"Coral provide Symbiodinium
with protection and surface area for photosynthesis, while the excess sugars created by the algae supply the majority of the coral's daily food requirements," he said.
He said expulsion of the algae removed the pigment from the corals' tissue, rendering them white or transparent, referred to as coral bleaching. If environmental conditions return to normal quickly enough, some corals may regain their Symbiodinium
and associated colour.
"If the Symbiodinium
is removed from the host and does not recolonize quickly, the corals can die.
"Mass coral bleaching events are a concern for scientists globally with recent events on the Great Barrier Reef highlighting the threat of elevated water temperatures to the heat of reef ecosystems."
source - phys.org