Ah, yes. French Frigate Shoals. The seascape of flocking birds, unexploded ordinances, and massive tiger sharks. Two of these I saw today. Which two? I will leave that up to your imagination. 🙂 French Frigate Shoals is one of the priority sites for my bioerosion experiments. I am just going to say right off the bat that these past two days were 100% success!
I am very lucky to be collaborating with NOAA’s Coral Reef Ecosystem Division on this bioerosion study. CRED collects water chemistry data, benthic community data, fish counts, calcification rates, and cryptofauna samples at 5 permanent sites at 4 atolls in the NWHI. They are allowing me to use their sites to deploy my bioerosion blocks and collect dead coral samples. At each of their sites they have a Calcification Autonomous Unit (CAU-pronounced cow) that is constructed with a small piece of rebar and a 5″ square PVC plate on top. Little corals and crustose coralline algae settle on the PVC and CRED calculates calcification, or accretion, rates for each atoll. This is quite fortuitous for two reasons. The CAUs are a perfect structure for me to attach my bioerosion blocks to and collaboratively, we will have complimentary data for both accretion and erosion rates at a given site.
Picture of a CAU with a bioerosion block cable-tied to it. Photo Credit: M. Donahue
I am collecting two different kinds of data at each of my sites: an assessment of the bioerosion community and the bioerosion rate. To figure out what little critters erode the coral substrate, I am sampling pieces of dead coral and fixing them with ethanol. Ethanol preserves all the animals that are living inside the dead coral so that I can identify them at a later time and then extract/sequence the DNA. The bioerosion blocks attached to each CAU are used to aquire bioerosion rates for each site, but I will tell you a bit more about how I get these rates in a later post. I am using some really cool technology in collaboration with Cornell University!
While attaching the bioerosion blocks to each CAU is quite simple, finding the CAUs is another story… Looking for these structures that are made for coral to settle on them, in the middle of the Pacific with no land around is literally like looking for a needle in a hay stack. The fact that we found all 5 of my sites at French Frigate Shoals is a HUGE success.
Can you find the CAUs? Hint: There are 3 in the picture and my blocks are already attached so it should be easier to find.
Fortunately, we had amazing condition today and yesterday. Flat calm seas, clear water, light winds, I could not have asked for a better two days to work. On our first day we even had a few visitors: 2 gray reef sharks and a white tip. The grey reef shark particularly seemed interested in our pelican float.
Grey Reef Shark number 1
We have finished all our ops at French Frigate Shoals and now we are on our way to Maro!
Here are some more pictures for your enjoyment. 🙂