CORAL AND ITS COHABITANTS
polyp but it is not the only one. Turns out, microbes play an important role in polyp health, much like they do in human health. Once considered invaders, the microbial community that inhabits our body’s orifices – the microbiome – is now linked to an ever-growing list of vital functions including taming our immune system and contributing to the health of the gut, liver and even the brain. The latest thinking is that the coral polyp, sitting right at the base of the evolutionary tree next to sponges, also relies on its microbiome for its health and immunity.
The coral microbiome resides in the coral’s mucus coating, gut and skeleton. It is effectively a chemical factory that produces a diverse range of products, including nitrogen and sulfur-containing compounds. Van Oppen suspects the repertoire extends to antioxidants – chemicals that could neutralise the oxidants produced during coral bleaching. If that’s the case, it might just be the genes of the coral microbiome that help it survive heat stress.
Finally, corals seem to have one more trick up their sleeve. Some colonies appear to adjust to heat stress in the same way that tomato plants do: they gradually get used to it. Gardeners harden tomato seedlings by gradually exposing them to warmer and warmer temperatures. The mechanism, dubbed epigenetics, does not alter the DNA code but reprograms it (by attaching chemicals such as methyl groups). There are glimmers of hope that corals can acclimatise to gradual change based on what happened to the reefs exposed to the devastating Indian Ocean mass bleaching event that occurred in 1998. When the 2010 bleaching event arrived 12 years later, those corals that had survived the earlier event appeared to be more resistant.
However, the bleaching events of 2016 and 2017 dashed any such hope for the Great Barrier Reef; whatever hardening took place, it was not enough to protect the reef.
Van Oppen and her colleagues are now tinkering with these four components of the coral genetic toolbox – coral genes, algal genes, microbial genes and epigenetic hardening. Most of the tinkering is taking place at AIMS in the wilds of Cape Ferguson.
AWAY FROM THE CROCODILES, sharks and snakes, scientists can safely carry out their experiments in what may be the world’s most sophisticated simulation of the sea – the $40 million Seasim aquarium, which has a state-of-the-art control room with the same design specs as those in a nuclear reactor. Scientists can observe remarkable things by programming the slowramping rhythms of the sea, the waxing and waning of daylight and temperature, and the CO2 levels that climb gradually at night as plants cease photosynthesis and their consumption of the gas. The computers can also precisely simulate the deposition of fine sediments, a feat that revealed for the first time how corals shed their mucus coating like a glove to rid their surface of sediment. Before scientists unleash any evolutionarily fast-tracked coral on the reef, its impact will be simulated at Seasim first.
Seasim may be safer than the waters of Cape Ferguson, but things get pretty feral here at spawning season. Once a year, generally on a November night after the full moon, corals spawn. On the reef it happens en masse, the waters turning cloudy with trillions of eggs and sperm. Before November, scientists from around the world pluck corals from the reef and bring them into Seasim. But not every coral species joins in on cue; they may be out of sync by hours or weeks. So breeders will stay up all night watching and waiting for the first signs that the coral are about to eject their tiny bundles of sperm and eggs. They collect the bundles, strain the sperm from the eggs and wait for the next species to spawn. It’s a harrowing wait: they have only a couple of hours before their captured sperm and eggs die.
AIMS researcher Lesa Peplow shows me a tank bearing the results of cross-breeding experiments with four species of Acropora: tenuis, loripes, sarmentosa and florida. She, van Oppen and PHD student Wing Chan have tested juvenile corals under the conditions of today and those predicted for the middle of the century (+1 degree and 685 ppm CO ). Encouragingly, some of the hybrid crosses showed greater survival than their parents under both conditions.
In another corner of Seasim, I am guided by Line Bay, a Dane who visited the Great Barrier Reef on
The latest thinking is that the coral polyp, sitting right at the base of the evolutionary tree next to sponges, also relies on its microbiome for its health and immunity.
MATURE POLYP Protective mucus layer Mouth Microbiome Free-floating polyp Attached juvenile coral Spawn: sperm and egg Mature coral Algae