This afternoon some fragments of Acropora hyacinthus were brought up and placed in tanks and at about 8pm they started setting (egg bundles were seen at the mouth of the polyps). At 9:10pm they started releasing their egg bundles (bundles of eggs and sperm). It was great! It’s almost midnight now so more updates tomorrow! We’ll be doing a dive tomorrow night so there’ll probably be more action! (and pictures!)

Here are some pictures

Coral fragments in flower pots

Before night fell the coral fragments (collected a day earlier) were placed in flower pots floating in a large tank. This is so that when the corals release their egg bundles, we can isolate the egg bundles from each colony (and cross fertilise them later).

Acropora millepora releasing egg bundles

About about 8pm (an hour after dusk) we could see pinkish egg bundles sitting at the mouth of each coral polyp. At this point, we would regard the coral as “set” and would most likely spawn within an hour or so. However, it was also possible that the corals would not spawn and somehow reabsorb their eggs, although I’m not quite sure how.

The corals that were setting in the tanks spawned at about 9pm. There were some others that didn’t spawn, but perhaps they will spawn the next day instead. Spawning started with just a few of the egg bundles being released, followed by lots more. Sometimes only part of a colony of a coral spawns.

After the corals release their egg bundles, the egg bundles float to the surface because they are positively buoyant. After about half an hour or so, it looks something like this

Egg bundles floating above Acropora hyacinthus

Note that these photos were taken after most of the spawning had already occurred because it’s best not to use camera flashes or any white light for that matter on corals that are close to spawning as it might mess up their cues. The corals depend on cues like sunlight, moonlight, water currents etc to know when to spawn. White light on a coral might make the coral think that it’s still day time and so it may not spawn. Most of the time we were working more like this

Checking for coral spawn using red light

At the end of the spawning session, the egg bundles were collected

Collecting egg bundles. The pink parts are eggs, the whitish parts are sperm

Each egg bundle contains a mixture of eggs and sperm from the same parent and self-fertilised embryos tend not to survive so well (and would also defeat the purpose of sexual reproduction). So we cross fertilised the eggs with sperm from another colony to get best results. All these were done in the lab and in-vitro fertilisation seems to yield more successful fertilisation rates than would occur naturally because we eliminate factors such as predation and increase chances of egg and sperm fusion.

18 hour old fertilised embryos look something like this:

Coral embryos

They kinda look like the eggs but slightly mis-shapened. But don’t worry, they’re good embryos that later develop into hard corals! Cool yeah? More updates soon!


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