Nubbins

When we pull up to a study site, the whole team goes to the bow. Sure, we have a latitude and longitude for where we're supposed to be, but the GPS can only get us so close. The best strategy is to peer through the water and see if you can spot anything familiar - like your experiment. 

The turbidity at Mecherchar is pretty high, so I wasn't sure if we would actually see the nubbin rack from the surface. We actually did! The rack was made from black, white, and gray PVC, so it had pretty high contrast and actually stood out. I was relieved that we found it again, and I'm pretty sure Cas's blood pressure spiked about 50 units with excitement when we spotted the rack. 

The missing, the dead, and some survivors on our rack

Once we determined that our experiment was still there, the next question was whether anything survived. Cas took on that task while Matt and I swam off to take care of something else. We actually had pretty good survival - about 50%! Some nubbins fell off the rack and had to be excluded. Many of them either bleached or fell victim to predators. But about half were still alive. We were stoked. 

It was even more exciting to have an experiment work after the previous day's disappointment. We wanted to collect tissue samples to tell how our corals had changed over the 6-month transplant. You see, corals are whole ecosystems. Every coral has within it algae and microbes, and those symbionts can be replaced by other species over time. While every organism has the same DNA throughout its life, the coral host and their single-cell partners can change what parts of their DNA are active. We call that "gene expression." If a coral gets different symbionts, different microbes, or the coral or its symbionts start expressing different genes, it could affect the coral's ability to survive in a stressful environment. Seeing how the corals have changed over 6 months will tell us how they acclimate to stressful conditions. 

Here's the thing: studying gene expression is super finnicky. To see what genes are active, you actually look for RNA - that's a molecule that is copied from DNA and carries the instructions to make proteins. RNA degrades super quickly. Insanely quickly. Like, leave it alone for five minutes, and it's vanished. 

To get an accurate view of gene expression, you really have to preserve the samples in situ. You want to get your sample into ethanol as soon as humanly possible, so you get a freeze-frame of RNA in the organism at that exact moment. For us, preserving samples in situ meant preserving samples underwater. Yep. Underwater. 

We came up with a pretty neat system, actually. We filled tubes with ethanol and carried them to the seafloor with us. One by one, we took a small chip of tissue from each of our coral nubbins. Then we turned an ethanol tube upside-down, opened it, placed the coral chip inside the lid, and screwed the lid back onto the tube. Ethanol is lighter than seawater, so most of it stays in the tube. You get perfectly preserved in situ RNA to study gene expression - voila! Back at the lab, you can transfer the samples to new tubes with fresh ethanol if you want. 

It was very satisfying to see one of our experiments working. Hopefully, we'll get good results!