I had thought that sea urchins moved too slowly to detect… until I saw them mating one magical evening in the Caymans. Sea urchins can move pretty quickly when motivated by sex.

I was coming back to the dock from a short snorkel, and was floating about 4 feet over a bottom covered by spiny sea urchins. I paused, and was stunned to find that they were moving. They were going amazingly fast – at least for them. And all of the urchins in my area were moving toward one point – a high rock with a single urchin on it.

One of the suitors reached the rock first and let out what looked like a puff of smoke. I thought this was premature ejaculation, since he was still 1.5 feet from the female, but he meant to do it. Nearly as soon as he released the sperm (or was it just a scent signal?) all of the other urchins stopped moving.

The male then moved close to the female. They got much closer than I had imagined spiny animals could get without poking each other’s eyes out. After a minute or so together, they moved apart about an inch and the female released eggs from the top of her body. She moved away a little, the male moved toward her and released sperm. They kept doing this, but I’m not sure of how long. When I emerged from the water the sun was nearly set and the rest of the guests had their pre-dinner beer buzz going nicely. I was probably in the water for over an hour. I don’t wear a watch or pay any attention to time when I’m on vacation, so it’s hard to be sure. And you know how time flies when you’re watching live urchin porn.