Lone survivor

Our lone survivor on the side of its tile.

We had one more experiment to check on in Palau: the juvenile transplant experiment. This is the experiment that actually got us funded to come here in the first place. It was designed to figure out whether the descendants of thermally tolerant corals can survive on outer reefs and help them recover from bleaching. After the disappointment of our delayed metamorphosis experiment, I was really curious whether our little baby corals would survive the transplant. Do you want guess? How many corals do you think survived six months after transplantation? 

One. 

Honestly, we're not even sure that one individual is from the experiment. It's pretty small and is living on the side of a tile. Most of our experimental juveniles settled on the front or back. It's possible that the one coral we found on the tile actually just settled there after we put the experiment out. 

Corals are extremely challenging to work with, so I'm not actually surprised that all of ours died. Even though we won't get publishable results from the juvenile transplantation, the mortality we observed is still informative. Coral babies are subject to any number of stressors that can kill them - not just temperature and light, but also predators and competition from algae. We've demonstrated that mortality in the post-settlement stage can be very high and constitute a bottleneck for coral populations. We've also shown that if coral restoration efforts want to use juveniles descended from thermally tolerant parents, they need to expect high mortality - or maybe just work with a different life stage altogether. 

The tiles that our corals were on didn't actually have that much junk on them - no thick mats of fleshy algae, no nasty overgrowth. I'm pretty optimistic that we could modify the experimental design and get better results. We could let the juveniles grow a little in the lab and get hardier before we outplant them. We could also shorten the duration of the experiment - maybe leave them out for one month instead of 6 months. 

We have a reasonable path forward, and in the meantime, we're learning a lot!