I’d planned something else for Friday, but once again a shiny dinglehopper has intervened.

Last night I witnessed something few people get to see, and I thought I’d share.

This is a sun coral (Tubastrea sp.), a variety of non-reef-building, large-polyp, stony coral that prefers dim lighting conditions:

Sun corals produce in two different ways. The parent colony can either clone itself (asexually) by producing new polyps that grow out of the “parents” sides or produce “planulae(singular “planula”), which are free-swimming larval babies that settle elsewhere on live rock and produce new colonies of their own.

In captive reef systems, most sun corals reproduce exclusively by cloning (if at all). They expand laterally by putting off new clone-polyps genetically identical to the parents. Production of planulae is exceedingly rare and almost never successful.

About six weeks ago, my sun coral closed up for about five days. It didn’t look unhealthy, but it didn’t open up to eat. It looked mostly like this:

A week later I discovered tiny orange spots on adjacent pieces of live rock, and within two more weeks the “spots” had developed into baby sun corals – evidence that the coral had produced planulae successfully.

A few days ago the coral went “turtle” again, and last night it opened up to feed. I had a feeling it was planning another round of planulae, sneaked into the room at 2am with a flashlight “to see what I could see,” and witnessed a minor miracle.

Each of the polyps opened its mouth in turn. Tiny planulae crawled out as the coral sucked in water, and then each parent polyp expelled water and planulae with enough force to send the baby coral larvae into the current. The planulae drifted across the surface of the rock and fell “to ground” across the reef. Once they landed, the planulae crawled across the rock, presumably seeking an acceptable location to “root.” Each planula was approximately the size of this period ( . ) yet fully mobile and alive.

Today’s shiny dinglehopper is life itself, in one of its many amazing forms. The ability to witness that life reproducing itself (against staggering odds, when you consider the size of a planula in the ocean, where these corals typically live) is an amazing gift. A year ago, I never gave much thought to how corals reproduce, but now that I know – and have seen it – I thought the rest of you might be interested too.

If not, Grumpy Fish would like to know why.