Gold record

Back in 2017, I worked with my German collaborators to finish a long-term experiment on recruitment in the Arctic deep sea. A lander frame with brick and plastic panels that had been deployed in 1999 was finally brought to the surface in 2017, and I had the opportunity to see what was living on it. Some of you may remember one of the most common species on the panels was the crinoid (sea lily) Bathycrinus carpenterii.

Some of my crinoid specimens - those stalks are tiny!

The more I looked at the samples, the more I started to see a pattern. There were two distinct sizes of Bathycrinus on the panels - one large, one small. I started brainstorming reasons why there would be two different sizes, and I hypothesized that the two size groups had individuals of different ages - one older, one younger. If that's true, it means Bathycrinus carpenterii might have had only two reproductive events in the 18 years the experiment was taking place.

Think about that for a second: if this species only reproduced twice in 18 years, that's a really long time between spawns! Most marine organisms reproduce every year, and some reproduce continuously. I'm testing my hypothesis by slicing open the stalks of Bathycrinus individuals from the long-term experiment. In a previous study, two scientists found that Bathycrinus had growth rings like a tree, so I'm hoping I can count the rings. (I also have to ascertain if the rings are annual, but more on that later.)

Biology's Greatest Hits (actually an otolith saw blade)

Slicing open the stalks of an Arctic deep-sea species takes a little bit of experimentation. As far as I know, nobody has ever done this before. Thankfully, Bathycrinus aren't the only marine organisms that have calcium carbonate structures with rings inside. In fact, fisheries biologists regularly slice open otoliths (ear bones) of the fish they study to measure rings, so I'm copying their methods. A generous colleague in my building has opened his lab to me and allowed me to use his otolith saw. I spent a lot of time experimenting in the fish lab today, trying to find the best way to slice open the stalks.

The otolith saw with one of my specimens

The first step was to buy and condition a new blade for the saw. When the blade arrived, it was packaged in clear plastic, exactly like a gold record a musician might display on their wall! I installed it on the saw, conditioned it by dipping the edge in glycerin and slicing into a "dressing stick," and then set to work with my specimens.

I had to glue the Bathycrinus stalks to microscope slides to hold them still. Then, by clamping the slide onto a rotating arm on the otolith saw, I was able to lower the specimen carefully onto the blade for slicing. To be honest, I'm not sure if the slicing is going to work because my specimens are so tiny. I'm speaking with my fisheries biologist colleague to see if he has any suggestions for working with very, very small specimens.

It will take a little work, but I'm excited to experiment with my specimens and determine their ages. If I succeed, I will establish a new method for the analysis of deep-sea species and will likely have some very cool results!