Settle

"You are only as much as you settle for." - Janis Joplin

Porites lobata larvae develop quickly. We discovered this last year. Eggs get fertilized one night, become larvae by the next day, and are ready to pick a spot on the seafloor just a day after that. The timeline is convenient because we don't have to stress and change their water and try to keep them alive for days on end, but it also means we have to be ready for settlement quickly. 

Just two days after getting our first spawn, we had to settle our corals. The process is relatively easy. We culture the larvae in plastic bins, so getting the larvae to settle just involves adding a tile to the bin for the larvae to settle on and a cue that makes them want to settle. Easy, peasy.

Yeah, you're not that naiive. Of course it's more complicated. Yes, we culture the larvae in plastic bins. Yes, we also get them to settle by adding a tile and a settlement cue to their bins. But there are several steps in between. 

The first step is concentrating the larvae. They've been in their bins for about a day and a half, and by now, any eggs that failed to fertilize have exploded. The water can be a bit mucus-ridden, so we want to get the larvae away from anything that smells like death. We want them as happy as possible for settlement. The second reason to concentrate the larvae is to make sure they get evenly spread among the tiles. Fertilization and therefore death may have been uneven among the culturing bins, and we don't want that variability to carry over to our settlement tiles. 

I didn't do a good job of photographing the 
process, but here are all of our completed
settlement bins! 

Matthew spent a while deciding the most gentle way to concentrate the larvae, and in the end, he settled on a slow-and-steady method. He used a siphon to draw the water (and the larvae with it) out of each bin and into a filter. To keep the larvae from being smashed on the filter, he placed it in a tub of water and bobbed it slowly up and down. That way, the larvae stayed in suspension. He propped the filter up on a wooden stand so that the incline of the siphon wouldn't be too steep. With his sunglasses on, bobbing the filter slowly over the wooden stand, he looked like he was part of a slow-motion drum circle. 

The next step is to prepare the settlement cue. After some trial and error last year, we decided the best settlement cue was a dust prepared from crushed-up crustose coralline algae (CCA). We collected some dead coral rubble with CCA on it from one of our study sites. When it's time to settle the corals, you make the dust by scraping the CCA from the rubble with a scalpel. Then you grind it using a mortar and pestle, pour off most of the water, and let the dust settle to the bottom. You suck the concentrated dust up with a pipette and blow it carefully onto the submerged tiles in the settlement bins. 

It took all morning and some of the afternoon to concentrate the larvae, clean tiles, add them to the bins, make the CCA dust, and then finally add the larvae to the bins. But it will be worth it if they settle!