CBASS

After we collected all the gene expression samples from our nubbins, we had one more goal. We brought back all the nubbins that were still alive to the lab and used them in an experiment. We wanted to find out how well our coral nubbins could tolerate heat. Remember that we collected nubbins from corals from two different sites. Then we planted half of the nubbins back at home and transplanted the other half to the other site. We're testing what controls thermal tolerance the most. Is it: 

Matthew working on the CBASS rig.

- who you are (the genes you inherited from your parents)

- who you live with (your algal and microbial symbionts)

- where you were born (origin site)

- where you've recently been (transplant site)

- or what you're doing (gene expression)?

Our experiment should be able to tell us! We're testing a lot of factors, so we had to have a large number of replicates - 108 corals total. Some of the factors might also interact, but that's ok. Corals are complex organisms! 

Ok, so how do we actually measure thermal tolerance? There's a protocol that's recently gotten a lot of traction in the coral research world called CBASS (pronounced "sea bass" - that really confuses people when they first hear it). It stands for Coral Bleaching Automated Stress System. You split the corals into four temperature treatments - we're using a control, +3 degrees, +6 degrees, and +9 degrees - and use programmable aquarium heaters to control the temperature in the tanks. You ramp up the temperature for three hours, hold them at temperature for three hours, cool them down for one hour, then take a measurement of photosynthetic efficiency - basically a measure of overall coral health. 

CBASS is nice and straightforward, and you can do it in a day. Thing is, that day is super intense. We collected all our nubbins one day, spent the evening cutting them into small pieces to split among the four treatments, then ran CBASS the next day. It was all-hands-on-deck. 

Some coral chunks in the CBASS experimental tanks.

Cas and Matt built up our CBASS rig in the wet lab at PICRC. It looked super fancy, got to be honest. Kim referred to it as a sculpture. 

When it came to time for the experiment, the aquarium heaters kicked on automatically. We were relieved! Cas monitored the temperature over the 6-hour run, and everything worked perfectly. When it came time to make the measurements of photosynthetic efficiency, we gathered in the wet lab wearing red headlamps (you have to do the measurements in the dark). We split into two teams: Kim and I maneuvered fiber optic cables to each coral in the tanks, while Cas and Matt operated the software. We would hold the cable on the coral for a moment, and then a ray of blue light would be sent down the fiber optic cable. The fluorometer would then measure the proportion of light returned by the chlorophyll in the coral. It's actually pretty cool to be working in the dark and then see the cable in your hand light up blue. 

Our first round of CBASS went very well, and we got great data! I'm really excited to see what the results will show!