Spawning Under a Full Moon

Work in construction as a rule, whether it be installing a slider door or dredging for natural gas, is inherently subject to unexpected delays from unlikely places. Since Chevron is trying to do right by the environment during this project, the source of delays are generally environmental. The project is facing a potential two week delay, translating into hundreds of thousands in monetary loss, due to an extremely full moon and thousands of little colonial polyps otherwise known as coral. A massive coral spawning event is due to take place on this 19th night of March; where little packets of genetic material will be simultaneously released into the sea.

I’m assuming you haven’t put much thought into coral sex, so let me take this opportunity to explain the process. For starters, corals are essentially a colony of polyps, polyps in turn are essentially small fleshy cup-like organisms with ‘arms’; think of them as very small anemones that build calcium carbonate houses to live in (in fact they’re in the same class as anemones Anthozoa). Coral polyps feed by capturing plankton with their arms, but they get most of their energy from zooxanthellae, mutualistic algae that live in their tissue. The polyp gives the zooxanthellae a home; the zooxanthellae in turn provide the polyp with sugar produced through photosynthesis.

Each polyp can reproduce in two ways. It can either engage in sexual reproduction where gametes (both eggs and sperm) are released into the water in a process called broadcast spawning; or through asexual reproduction, where an individual polyp will bud a clone of itself, which then matures into a genetically identical polyp. Like Richard Simmons, corals are hermaphroditic, producing both egg and sperm.

The ocean is a very big space from the perspective of a polyp (if they in fact could perceive their world…I wonder what they would ponder), so if each polyp released its gametes at random intervals, the chances of gametes from neighboring coral colonies interacting would be slim, thus defeating the purpose of sexual reproduction; which is the produce variation in the gene pool and ‘spread the seed’ so to speak, through sex. It would be like showing up to a party at 7am, after everyone has already passed out from excessive drinking, and expecting to make some offspring…it’s just not going to happen. Better to show up at the right time. So corals have evolved a method of insuring their gametes get put to good use, with a synchronized broadcasting of sperm and eggs during one night out of the year, across an entire region. This allows for the greatest chance for the coupling of sperm and egg from different coral colonies throughout a reef.

Broadcast spawning events typically only happen once a year, so it’s a big deal, and its timing depends on three key conditions. First, an increase in water temperature triggers the production of gametes. Second and thirdly, spawning events are related to the diurnal and lunar cycles, only happening in the dead of night during a full moon.

The sea becomes a soup of genetic material, billions of sperm and egg packets drift around the reef with the currents, and when the two meet, they form a kind of embryonic coral called a planula larvae. The planula will drift around for days to weeks, until it eventually settles on the sea floor, where it then undergoes a radical change leading to a new polyp. The founding polyp will then begin asexual budding and produce thousands of clones. Give these founding polyps a few hundred thousand years, and they will produce something as massive and awe inspiring as the Great Barrier Reef.

So, all of this sex will be happening under my feet tonight. Given the rarity and importance of the event, dredging will cease for at least 10 days to avoid interfering with the fertilization process. At the stroke of midnight, coral polyps all across the Barrow Island region, gravid and ready to burst, will release their seed into the sea under the light of a full moon. At least someone is getting some action.

The moon, as a side note, will make a very close approach on its orbit around the earth. In fact closer to earth than it’s been in two decades, 221,567 miles away. A historic night indeed.