Today was a big day for me. I got to graduate some of my baby urchins from glass slides onto coralline rocks. They were growing very quickly on the slides, chowing down on scum faster than I can grow it, so now it's time for the biggest ones to really put their Aristotle's lanterns to the test and chew up some rocks.
Coralline algae are red algae that have calcified cell walls, giving them a crunchy texture. They come in two morphs--erect branching forms and as encrusting sheets--and are pink in color. The corallines that I'm using for urchin food are growing as sheets on rocks. In the field it is not uncommon to see little urchins on coralline rocks, and their teeth are more than capable of grinding up the calcified algae.
So today I used my trusty frayed paintbrush to scoop up a total of ~90 urchins from their slides and dropped them onto rocks. I should have taken a picture of this valuable tool of mine, so you can see just how low-tech (and cheap!) my type of marine biology is.
The largest urchin on this rock has a test diameter of ~2800 µm. Almost 3 mm now!
Here's a closer view of three of the urchins in the photo above:
It didn't take long for the little urchins to start crawling around on their new substrate. I think they'll be happy with this more natural surface to explore and food to eat.
In the meantime, the remaining babies will stay in their jars or on their slides, eating scum. I will continue graduating urchins to rocks as they get too big for slides, feeling more nostalgic each time.
Just think, only 97 days ago these urchins were zygotes! It's not often that you can say that you've known an organism for its entire life, from the moment of fertilization. I am grateful for the privilege of having the opportunity to undertake such an intimate study of these animals' lives. Although I try at least once every year, this is my first successful urchin spawning since 2012. Those animals, by the way, are what I call my most perfect urchins because, well, they just are. I had originally thought I could use them for dissection, but after caring for them as larvae and the three years since they've metamorphosed, I just can't bring myself to sacrifice them. They are simply perfect.
I don't think I could ever get tired of this.