Perfect timing: part 2

A Metridium senile larva

I pulled into the parking lot at work. It was 6:30 am. Every morning, I stopped by the lab before my safety training class to take care of my larvae. Every afternoon, I went straight back to the lab as soon as my training was finished. Sure, I was burning the candle at both ends, but I was getting amazing data. 

I have wanted to study the larvae of Metridium senile for several years now. I actually had a lightbulb moment in 2017, when my husband dragged me to a dive show north of Boston. We had just started dating, and he wanted to get me interested in SCUBA diving (the plan may have worked a little too well). There was an exhibit at the dive show about the shipwreck Andria Doria, which rests just south of Nantucket. As we walked through the exhibit, I stopped short. Every photo of the shipwreck on display that day had the same species in it: Metridium senile. I new Metridium well - it was the dominant species on a shipwreck I studied in grad school. Seeing the exact same species on Andria Doria, several hundreds of miles away from my old study site, was actually a bit eerie. 

In the years since, I have laid eyes on many more shipwrecks, and at least in the North Atlantic, every single one has had Metridium senile on it. No other species shows up that often. Why is Metridium so good at living on shipwrecks? I just have to know. 

My first guess is that it has to do with the larvae. Metridium, like most anemones, can only crawl short distances as an adult. The major opportunity for an individual to spread to a new environment occurs during the larval phase. Larvae are carried around by ocean currents, so they can travel pretty darn far. Maybe the reason Metridium lives on shipwrecks is just that it can reach them, and not many other species can. Anemones can split themselves in half and reproduce asexually, so it would only take a few larvae to found a whole population. If those few anemone larvae make it out to a shipwreck before their normal competitors or predators arrive, they could divide over and over again and dominate the whole thing. A combination of long-distance larval dispersal and asexual reproduction could explain the patterns I see. 

To test my hypothesis, I have to learn as much about the larvae as I can. Nobody has written a truly comprehensive description of larval development in Metridium before. There are scraps of information buried in papers from the 80s, and even those few reports are contradictory. Some researchers say the larvae "swim strongly," others say they just lay at the bottom of the dishes. One account describes the larvae as plankton-eaters; another says they live off of fat reserves from their mom. It's possible that all those accounts are correct - maybe Metridium larvae are super variable. Maybe that's why some of them end up far away from their parents on a shipwreck. 

I have waited years for someone to fund my Metridium research, but now I finally have the resources I need. This experiment is my chance to test an idea that started growing in my mind in 2017. It's a lot of work to maintain larval cultures, collect the data that I need, and hold down all my other responsibilities, but you know what, it's worth it. I am so freaking excited about this experiment.