CO­RAL AND ITS CO­HAB­I­TANTS

Cosmos - - Coral Evolution -

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

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