Coral Sex

Work has been rather slow lately, a lot of sifting through websites looking for meteorology stations, and where the data actually comes from. Hopefully in the next couple weeks something tangible will come of it, but for now it’s not all that exciting to talk about.

So, this week I  have a post from outside of work that happens to be ocean related. A few weeks ago I got the chance to go scuba diving with the coral spawn! For anyone who has not heard of this already here is a quick overview of how coral reproduce.

Coral is made of colonies of individual polyps. Individual polyps can reproduce asexually- splitting into two, which is how a colony grows. And a whole colony is essentially made of clones of one original polyp. Because they cannot move to reproduce sexually, corals release their gametes into the water column where hopefully they mix together with another genotype and produce genetically distinct offspring which will settle and begin to divide and ultimately form a new colony. (This is an oversimplification of the lifecycle if you want to know more take Invertebrates or look it up). The ocean is a big place, and the chances of fertilization occurring if corals were releasing gametes at random would be incredibly low, so many species have evolved to precisely time the release of their gametes to within a couple of hours on one night a year, so that the maximum number of gametes from the most different colonies are in the water at the same time. It is still unclear exactly how they time this, but it is related to the phases of the moon. It is also different for different species and different locations around the world. But here in northern Colombia the species we went to observe (sorry never learned what species it was) spawns one week after the first full moon of September (this year it was 31 of August) about 4 hours after sunset. This species is hermaphroditic, and releases gamete packets that contain both sperm and eggs.

Please note: All underwater photos in this post were taken by Jorge Granados, a divemaster with Diving Planet dive shop. I have ‘borrowed’ them from his Facebook profile. Any other photos were taken by me.

I left work early on a Thursday to go to the dive shop, and we took a boat out to their second location the Rosario Islands (about an hour South-East-ish of Cartagena). The plan was to do 3 dives, spend the night on the island and be back to Cartagena by 9 the next morning.

Isla Grande, Rosario Islands. Looking back towards Cartagena.

Dive flag

Dive dive dive!

Dive gear on the jetty

Ready to go!

We did an evening dive first, about an hour before sunset. We didn’t see too much exciting, though we killed 8 Lionfish (Lionfish are invading the Caribbean and are destroyed on sight). We later ate them for dinner…

And then we did a night dive just after sunset. Way more invertebrates were out after dark, tons of shrimp and prawns with reflective red eyes. Several Spiny Lobsters and some big crabs. Brittle Stars were also all over the place too, some hiding in the corals with only their arms sticking out, and some bright red ones out in the open.

Spiny Lobster

Brittle star and also some polychaete worms (the little squiggly things in the foreground)

The third dive of the day was the one we had come out for… The timing for the start of the spawn is pretty accurate down to about an hour, but to avoid wasting air waiting for it to start one or two divers who know what to look for go down first and wait for it to start before signalling to the surface that it is time to get in.

It was slow to start, a lot of the colonies had the egg packets ready to, but they weren’t releasing them yet. Each polyp had a small pale pink ball about the size of a pin head in its centre. It took about 10 minutes before the first colonies started to release their packets, but then over the next 15 or 20 minutes colonies everywhere where doing it!

Coral before releasing gametes

Getting ready! Some packets are just starting to come free.

Starting to release gametes


More spawning!

As things were winding down with the coral, myself and a few of the other divers (including cameraman Jorge) got a bonus show! A couple of octopuses! The first one hid quite quickly, however the second one crawled along the coral and did some colour changing and even tried to catch a small crab while we were watching!

Little octopus!

Not too much later the spawning was pretty much done, and it was time to surface and head back for land and dinner (previously mentioned Lionfish!).

Spent the night in a hammock. And the next morning we were on the boat back to the city by about 8. I made it in to work by 9:30 (start time for us is supposed to be by 9, so considering I was coming in from an island half an hour late isn’t too bad…).

I will hopefully have some work related news this time next week… Or else I may have schedule another dive trip.


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