I know you know

 "See the rivers flow
Heading for the ocean
I know that's where we belong"
- "I know you know" by Ásgeir

Ah, the beginning of spring. Temperatures jump up to a more tolerable range, days lengthen, and there suddenly seem to be birds everywhere. I must admit I'm enjoying it. As an extra bonus in 2021, people are getting vaccinated! I know and you know how big of a deal that is. 

Earlier this week, I had a chance to start a new spring project. I'm trying to figure out whether an established technique (measuring carbon and nitrogen stable isotopes) can be used in a new way to reliably identify the diets of marine larvae. The theory goes like this: the higher up the food chain you are, the more heavy isotopes you accumulate. If you eat phytoplankton, you should have relatively low ratios of heavy isotopes, but if you're an apex predator, you should have pretty high ratios. People have been using stable isotopes to characterize the diets of marine species for years, but I can find only two studies that have done it for larvae. Each of those studies used just a single larval species. I suspect that studies on more species would reveal new information. 

Animals in jars. The scientist's dream.

For larvae, it's not so important exactly what they're eating as whether they're eating at all. Some larvae feed in the water column, but some rely more or less on energetic yolk they get from their mother. These two groups of larvae - feeding and non-feeding - have very different dynamics and pressures to contend with while they disperse to their new homes. 

The first step in my study is to use two species with known larval feeding types and compare the isotope ratios in larvae to their mothers. This exercise should establish my baseline - do larvae have isotope ratios that match their mothers when they are born? For the first step, I picked the slipper limpet Crepidula fornicata, which has a feeding larva, and the tunicate Didemnum sp., which has non-feeding larvae. On a SCUBA dive under the WHOI pier, I collected adults of both species, stuck them in seawater in my lab, and waited for them to spawn. 

Well, here's the thing. It's early April. The water temperature is 6° C. I'm not quite sure about Didemnum, but Crepidula never, ever releases larvae before it's 10°. I spot-checked some of the adults I had collected, and none of them seemed to be brooding egg masses. Drat. 

The good news is that I have 3 incubators in my lab with fine temperature control, so I can slowly warm up the adults and hope for the best. Animals never operate on human schedules - we have to conform to them - but in this case, the worst possible outcome is having to go SCUBA diving again. Hardly a punishment, if you ask me. For now, I can tell you that it felt really good to get my hands salty and work with live animals again. It's going to be a good spring.