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Corals are All Business, No Romance
Posted on February 13, 2015
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The staghorn coral is the one with branch-like protrusions in the middle.

There’s no love or romance in coral reproduction. It’s just eggs, sperm, and let’s get reproducin’. While Hannah Evans, senior biologist at the Vancouver Aquarium Marine Science Centre, says there’s coral spawning going on regularly in the various tropical exhibits, she’s keeping a close eye on one species in particular: the staghorn corals (Acropora micropthalma).

Egg-sperm bundles under a microscope.
Egg-sperm bundles under a microscope.

During an exhibit clean the other day, she picked up a coral fragment and noticed a pink and clear jelly-like substance, which she quickly identified as “egg-sperm bundles” (eggs are pink, sperm is clear). Being able to produce both eggs and sperm makes this animal a hermaphrodite. These corals have never spawned in the four years that they’ve been at the Vancouver Aquarium, so Hannah will be keeping a close eye on them.

Whether these corals will actually spawn though is still a mystery. In the wild, corals spawn when set off by certain natural cues: length of day, temperature of water and the lunar cycle. At the Aquarium, the lighting and temperature are regulated by Aquarium biologists  with the photoperiod and temperature remaining constant throughout the year, and the corals don’t have access to moonlight or lights that mimic the lunar cycle, so it’s possible that they won’t spawn at all. Instead, they might just reabsorb the eggs or hold on to them, perhaps indefinitely.

Hannah checks on the corals behind the scenes.
Hannah checks on the corals behind the scenes.

Hannah says the staghorn corals spawn like clockwork six or seven nights after a full moon in Guam, where she volunteered in coral conservation. But she won’t be concerned if she doesn’t see the same type of behaviour here. Hannah says seeing the bundles at all is, “a good indication of coral health because it takes a decent amount of energy to produce eggs.”

Written by Karen Horak, writer-editor, content and digital experience at the Vancouver Aquarium.

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