We spent the morning of the 4th day making sure that everything was in place for our phytoplankton incubation experiment to begin, the main reason we were on the Endeavor in the first place. Diksha and Vignesh had spent the weeks leading up to the cruise planning it all out and finally it was about to happen. With the towfish in place and all the bottles pre-labeled, we were ready to start collecting seawater.
The fish was deployed around 1300 – it took two of us plus two Endeavor crew members to get the towfish connected to the davit system and launched over the side of the vessel. In the photo below you can see what it looks like when the fish is properly deployed – doesn’t look like much if you haven’t seen this before as the actual “towfish” part of the setup sits below the surface of the water, at a depth of 1-2 meters. The towfish itself is a torpedo-shaped weight (actually a retired bathythermograph) that glides through the water as the ship is moving and allows us to collect surface water.
A long section of tubing pokes out in front of the nose of the towfish and then runs along its back, up around the rope that attaches the fish to the davit, and eventually to a pump that is sitting on deck – if you were taking this photo the pump would be on the ground right behind you. The white line you see extending over the water from the bottom of the photo is this piece of tubing, and if you look closely you can see where it joins with the rope and then disappears underwater. Then there is a second length of tubing that runs from the pump to our clean bubble in the ship’s lab where we bottle the samples- all in all, approximately 130 ft of tubing! Huge shout-outs to Dr. Ana Aguilar-Islas of the University of Alaska Fairbanks for lending us the towfish, and Dwayne “Whitey” Adams of the Dartmouth Apparatus Shop for helping us put together the needed accessories.
We needed to start the incubation experiment today to have enough time for everything, even though we eventually found out that a patch of water we passed through much later in the cruise would have provided a greater concentration of phytoplankton for us to experiment on.
In total we had 27 bottles to fill for the experiment – 9 different treatment groups that were each done in triplicate. We used the fish to collect about 40 L of seawater to subsample from – more than we needed, but always better to err on the safe side.
Diksha had the most experience performing this type of experiment before, so she filled all the bottles from our bulk supply using different types of mesh to create different size fractions of phytoplankton. We then placed all the bottles in the incubator on the back deck and left them for 24 hours so the phytoplankton could acclimatize to the bottles before we changed their environment even more.
We spent the rest of the evening in lab using the leftover water to sample for initial parameters (see featured photo), and we were thankful for the Bluetooth speaker that Vignesh had brought.