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The Tent Brigade
by Jen Smith, head researcher on the Benthic Team
Prior to setting out on this expedition, I really had no idea how the Benthic Team was going to accomplish the goal we had set: performing three separate experiments at each island given no more than four days each. It seemed impossible. Now, after our fourth island, we have settled into a very efficient groove, our procedures have been streamlined.
On day one at a new island, our first task is to set up the seaweed (algae) growth experiments known as the DAWGS and described earlier here. Our goal is to measure the rate of growth of some common species. Because we have such a limited amount of time at each island—three days really isn't long enough—we need to get these experiments up and running as quickly as possible. Usually Jill and Gareth attach the small protective cages to the bottom while Nichole and I carefully secure our measured algae samples inside the cages with plastic clothespins. The cages are used to protect our samples from hungry herbivores. Then just prior to leaving an island we retrieve the cages with their samples and we measure the change in size of the algae.
Our most elaborate experimental setups utilize our custom designed benthic tents or cBATs. With each of these we can measure the photosynthesis and respiration that takes place within a 1 m × 1 m × 1 m volume sitting on the reef floor. To set up and install six tents takes six divers two 60 min dives each to complete…depending on conditions, of course. First we lower the hardware which includes: (1) six tents; (2) six 12 ft pieces of heavy steel chain weighing 25 lb each; (3) hammers and chisels; (4) steel stakes to attach tents to the bottom; (5) six Eureka Manta sensors that measure oxygen, temperature, salinity, and pH; (6) six marine grade Sartek batteries; (7) six underwater pumps; (8) lots of very large zip ties; and (9) miscellaneous tubing, plumbing, and other odds and ends.
Since we are working at 30 ft depth, this lowering of equipment is a bit of a task. It requires free divers carefully guiding all of it to the bottom, and by "free divers" I mean Gareth. Finally the SCUBA divers drop in and arrive on the bottom at what looks somewhat like the site of a yard sale. We begin assembling our tent building supplies and then fall into our positions. Nichole and I select the sites where we will attach the sensors so as to span the range from high to low coral cover at each island. Once the sensors are attached, Jill picks up a tent and secures it closed. Gareth, Mark and I fall into place with one of us on each of the three tent corners. As Jill carefully swims the tent down to the bottom, each of us grabs one of the corner cables, a steel stake, our mallet, and some zip ties.
Tent assembly begins by securing each corner to the reef with a steel stake. Note: It can be inherently difficult to anchor a steel stake into the reef floor because often the reef is either (a) as hard as cement, or (b) as fragile as hard candy. When, after struggling a bit, we have the three corners secured, we grab one of the 12 ft pieces of chain and drape it around the tent resting on the skirt so as to make a seal between the tent and the reef bottom. We use extra reinforcement to ensure that there are no gaps or openings where the skirt meets the reef. If the conditions are particularly destructive, we need to check and recheck the tents every day to ensure that we have no losses.
Side Story: I was relieved when the expedition left the highly-exposed reefs at Kingman for Fanning Island that I remembered as being such a beautiful atoll with somewhat more relaxing conditions. We arrived at our tent site, carried out our circus act of lowering everything into the water, and then spent the next two dives expertly attaching tents to the reef floor. When we climbed back onto our Zodiacs, we exchanged high fives, impressed as we were with how well everything went despite the strong surge we encountered underwater. (Surge, the back and forth motion you experience underwater as a result of waves passing by, can be gentle or powerful.) The next morning we head out to the site to collect water samples from the tents, as usual. Gareth jumps in to assess the situation and yells, “All of the tents are gone!” Our first reaction was “no way! How could this be?” After a closer look he realized they weren't all gone, but definitely two of the six have disappeared completely, leaving no evidence as to where they might be. At least our expensive sensors remained, along with other heavy items like the chain. After making our next dive there and feeling the intense surge ripping us back and forth, we understood why the tents suffered some casualties. This type of research work is clearly not feasible under extreme diving conditions. Perhaps, we consider, this is why no one else has attempted to do what we are doing here on the reef slopes in the Pacific where wind and waves are the name of the game. We feel very fortunate to have gotten the data we have!
After the tents are secured to the bottom, the plumbing team—Nichole and Tracy—move in to do their work feeding tubing into the tents. This tubing is then connected to a battery-powered pump that circulates the water inside the tent and allows us to conveniently sample water from inside every day on demand. Once the pumps are installed and checked, we are nearly finished. We collect our first water sample by simply connecting a Niskin bottle to the tubing and turning the pump on to fill the Niskin, and off we go. These water samples will be later analyzed for an array of water chemistry parameters that will allow us to determine reef community metabolism.
At the larger islands we have had four to five days to do our experiments, but for the smaller islands only three, which means tent assembly on day one, tent sampling on day two, and tent dismantling on day three. As you can imagine, the days go by very fast. It is all worth it when we bring the sensors back onboard, download the data, and see nearly continuous sampling of the reef bottom during each of our deployments.
As if this schedule weren't enough, the benthic team is also doing shipboard experiments to determine how the physiology of the same species of coral and algae vary from island to island. Specifically, we are asking if the same species collected from the same depth in the same habitat show physiological differences that may be related to local human disturbances or to differing oceanographic conditions. We run two of these experiments per island. This work involves myself, Nichole, Gareth, and Jill all collecting organisms in the field, usually on day two. Then begins the fun. Nichole and I spend the better part of six hours in the sauna…literally. The ship has a sauna that we have converted into a physiology lab where we can control the light level. Here we expose the organisms to progressively higher levels of light and measure how much oxygen they produce. (Recall that the coral animals host algal symbionts, the zooxanthellae, that carry out photosynthesis.) This may sound easy, but we have to make these measurements in airtight chambers under precisely controlled conditions, such as at a constant temperature and with well-mixed water. We have a fairly elaborate aquarium system that we brought thousands of miles with us. Furthermore, the sauna is not for everyone. It’s a good thing Nichole and I are not prone to seasickness.
Each of the science teams on the cruise have their own mini-circus with various props and activities that all need to be coordinated and used safely and efficiently. Speaking as the leader of the benthic team, I can say that our circus is satisfyingly beginning to feel like organized chaos.