Perfect timing: part 3

Settled larvae in my culture dishes

I sat down at the microscope with a dish of anemone larvae in one hand and a glass pipet in the other. Time for a water change. For about a week and a half, I had been tracking everything I could about my Metridium senile larvae - size, shape, buoyancy, swimming speed, survival. All those parameters would inform a high-resolution model of their dispersal, so I needed to record everything. 

Peering into one of my dishes, I noticed something I hadn't seen before: small blobs attached to the glass. They were about the size and shape of a larva, actually. Same color, too. I sucked up a little water with my pipet and blew it on one of the blobs. The blob did not move. It was firmly attached to the dish. 

Zooming in, I noticed that the blobs had a bit of internal structure. A central point, some pale lines radiating out from it. A mouth and septa. Just like a juvenile anemone. 

Ladies and gentlemen, we have settlement! Those blobs can only be one thing: Metridium larvae that have metamorphosed and attached to the very dishes they were growing in. I let out a little squeal, then grabbed a pen and my lab notebook. 

Rearing a larva to settlement is a big deal, especially for a species you've never worked with before. Ironically, I had tested various settlement cues on my Metridum larvae as they grew. They didn't metamorphose in response to chemical cues from adult anemones, potassium chloride, magnesium chloride, or a scratched-up, rugose surface. Maybe I tested them too young, when they weren't ready to settle. Or maybe they didn't like the cues I gave them. Either way, the blobs in my dish were a good sign. Settlement in the lab was possible for Metridium, and I could calculate how long they took to develop. 

Another interesting component of my experiment is that I'm actually culturing the larvae at 4 different temperatures. The first settlers I found were in my warmest temperature, 20° C. A few days later, I had settlement in 10° C cultures, and some 5° C individuals settled a few days after that. I expected that development would be slower at colder temperatures, but now, I know by how much. 

My Metridium experiment is going incredibly well, and I'm accumulating amazing data in my notebook. I am so glad I finally get to study this amazing species!