This will be my last post — sadly. It seems like yesterday that we arrived, but as with all field work our research is done, we’ve packed up and cleaned the lab, and the shippers came today to pick up our scientific gear. An exhausting end, but well worth the effort. The field work was a resounding success, even if we will not know some of our results for some time to come. I want to thank Stephanie, Rafel, Marta and Celia for the photos that they gave to me for the blog, and especially Stephanie for some of the underwater video footage. On behalf of our scientific party, I also want to thank the personnel at the station who were a fabulous support team for us – Hinano, Frank, Val, Miriama, Tony Jacque, Neil, Vaimiti, and Irma–thank you so much for your hospitality, food, expertise and friendship, all of which made our stay not only productive but enjoyable — Mauruuru from all of us. Your smiles and help made the work, as tiring as it was, much easier to accomplish. and thank you Steve you’re our favorite LTERer……
To end, here is some fantastic video footage that Steph took when she and Marta went to sample the coral (Acropora) and surrounding water to look for changes in the chemical composition of the water over a day-night cycle (https://youtu.be/OFYy965nqzw).
As much as oceanographers dread these studies because of all the work they entail, it is nonetheless quite important in nature to study how the physics, chemistry and biology of the biosphere vary with daily cycles of light and darkness. This is true no matter what sunlight-driven ecosystem is under study: some organisms come alive at night and “sleep” during the day while others adopt the opposite strategy. The chemical fingerprint of the environment changes as organisms’ activities change. Likewise solar warming may heat up the water to produce a daily thermal mixed layer near the sea surface that goes away at night. Daily heating of the atmosphere can also produce turbulence and winds which will affect for example gas fluxes out of and into the oceans and atmospheric aerosol formation from bursting bubbles and breaking waves at the sea surface; and of course sunlight produces ultraviolet radiation that can affect microorganisms in the photic zone. We do not know in many ways what to expect with respect to day night cycles, especially as they may apply to coral reefs. It is well known that coral reefs come alive at night, and we therefore expect to see day-night differences, especially with respect to aspects of the coral reef that we are studying–microorganisms’ activities, volatile gas production, or DMSP and acrylate biological consumption.
We’ve already completed two day-night studies separated by a week from each other. The first study was done in the back reef (BR) and the second in the open ocean at the station we designated as “OO” — see my sampling map from an earlier blog. Both studies were conducted over a 30-hour period, with some of the experiments continuing on for another 12 hours. For each study, the first sampling started at 0400, about one-and-a-half hours before sunrise, and sampling continued every six hours thereafter. We made the same complement of measurements that we made during our transect sampling, except that no light measurements were made at night for obvious reasons. I focused on how quickly acrylate and DMSP were consumed by the microbes (see one of my earlier blogs for more details on these two compounds), but I won’t know any of the results until the samples are analyzed back in Syracuse, NY. I expect that rates of consumption will be higher in the reef compared to the open ocean and that rates will be higher at night compared to the daytime due to sunlight-driven photoinhibition of microbial rates during the day, primarily as a result of extended exposure of the microbes to damaging ultraviolet (UV) radiation from the sun.
We get very tired from doing this work. My family know my sleeping habits all too well. Here’s a photo of me taken by Celia after a long night:
During our 30-day stay at the field station, there are many different kinds of samples that we’ll collect and experiments that we’ll conducted–some experiments such as the photochemistry study we’ll do at the station and some we’ll do on site in the ocean. I discussed the photochemical experiments in a previous blog post. In this blog post, I’ll talk about other samples that we’ve collected and experiments that we conducted. One of the more interesting samples are the ones that were (or will be) collected close to the coral using a glass syringe with Teflon tubing and a valve attached to the inlet. This type of sample is collected by a diver. We do this type of sampling because we expect there to be chemicals emitted by the coral into the surrounding reef water, and the concentrations of these chemicals should be highest very close to the coral, with concentrations decreasing away from the coral. The difficulty in collecting this type of sample is trying to hold position, especially when there is a current or waves going back and forth, which was the case when Stephanie collected the coral sample at the crest ocean station (https://youtu.be/P9JMLpLy19g).
One of the more interesting hypotheses in oceanography is that when the oceans are viewed at very small scales (e.g., micrometer) they are not well mixed, even when parameters such as temperature and salinity would suggest otherwise. At small nanometer to micrometer scales, microorganisms can sense and respond to chemical gradients. The chemical gradient is the change in the concentration of the chemical in the water as one moves away from or towards the source of the chemical. The source may be a microorganism, a coral, a fish, etc. To test this idea that some motile bacteria are attracted to chemical plumes in the seawater, my colleagues Drs. Justin Seymour and Jean-Baptiste Raina (JB) deployed an in situ chemotaxis assay (ISCA) in the water. The assay consists of several silicone wells, each of which is “loaded” with a chemical of interest, which when deployed in the water diffuses out of the well to create a chemical plume that some motile microorganisms may respond to. If they respond to the chemical, they are trapped and subsequently identified using molecular biological techniques. With their method, Justin and JB can determine what bacteria are attracted to the chemicals contained in the wells. Chemicals they are testing are ones that are thought to be important in coral reefs such as acrylate, a compound that I am studying during our field study in Mo’orea.
Another kind of sample that we collect is the sea surface microlayer. The sea surface microlayer is an important interface between the oceans and atmosphere; it’s biological and chemical composition has been shown to be quite different from the underlying seawater–organic matter, metals, and microorganisms can all be enriched in the sea surface microlayer relative to the underlying seawater. Organic surfactants that concentrate in the microlayer affect physical and chemical process at the interface including gas exchange. We collected a 50 micrometer thick layer of the ocean surface using a glass plate (https://youtu.be/szZMf8_Ywxk). This takes some time because for each dip, we only collect approximately 9 mL of seawater, and in the attached video we collected more than 1 liter of microlayer seawater. Our plan is to test the photochemical properties of this water to see how it compares to that of the underlying seawater.
There are many other experiments and samples that we’ll collect during our stay in Mo’orea, but I’ve shared some here with you so that you can get a sense of some of the science that we’re doing. Now for a few nice photos of images that we’ve seen while at Gump.
We’ve been really busy so I’m a bit behind with my blogs. Early on in our stay at the Gump Station, we were approached by Frank Murphy who invited us to sample the Tetiaroa Atoll and give a lecture to the guests and staff living or visiting the Atoll. Of course we were excited at the idea and enthusiastically agreed to go and soon, since the weather and seas were calm. We headed to Tetiarao, an atoll approximately 60 km NE from Mo’orea, by boat. The seas were calm and the trip took about two hours.
Lots of time on the way over for conversation and planning for our upcoming lecture and sampling in the Tetiaroa Atoll.
There is only one entrance to the inside of the Atoll by water, and this entrance is for small boats only.
Once you’re inside the atoll, the scenery is beautiful at every turn.
Of course we consider ourselves very lucky to have the oceans as our laboratory.
When we landed, Frank, who is the director of the Tetiaroa Society, showed us around the island, highlighting the research facilities, the laudable goals of the Society, and the nearly 100% self-sustaining nature of the facilities on the island, with solar power, deep-seawater used for air-conditioning, and an extensive recycling program. Several of us used bikes to tool around as this is the main form of transportation on the island.
In the evening Rafel and I gave a lecture to the guests and staff at the hotel on our project, and the importance of our work in the context of understanding how coral reefs function and how they are connected to the larger view of the the earth’s biosphere and climate change.
The next morning we left to sample (1) a freshwater lake on one of the islands associated with the atoll, (2) the main lagoon in the center of the atoll, and (3) the reef crest just outside of the atoll. Even though we sampled three discrete sites, we also measured several parameters continuously in and between the sampling sites using an underway pumping system connected to two laptop computers onboard.
The freshwater lake that we sampled was used by fishermen for centuries as a source of drinking water.
April 7, 2018. Today I conducted an experiment to determine how much acrylate was produced in seawater when the seawater was exposed to sunlight for the entire day. The samples were filtered to remove algae and microorganisms so that we could just determine how much acrylate was produced from the organic matter in the water and not how much was produced by the microorganisms. When sunlight interacts with the organic matter in the water, the ultraviolet (UV) radiation component of sunlight (exposure to UV is what gives us a sunburn) causes chemical changes in the organic matter (a term referred to as photochemistry). The filtered seawater samples were placed in a special glass called quartz that is transparent to all wavelengths of solar radiation the reach the earth’s surface. Some of the quartz tubes were wrapped in several layers of aluminum foil; these served as dark controls. Once the quartz tubes were filled with water they were placed in a shallow water bath that had seawater flowing through the bath for the entire day. We also added small, capped glass vials containing chemical light meters (called actinometers) in the same water bath so that we could quantify the total UV dose that the samples were exposed to during the day. The nitrate actinometer gave us the UV-B dose (UV-B, 290 – 320 nm) and the nitrite actinometer with a Mylar film (this film removes the UV-B) gave us the UV-A light dose (UV-A, 320 – 400 nm). Humans cannot see the UV portion of the solar spectrum, but the UV component of sunlight has the most energy to break bonds and give rise to chemistry (and sunburns for us!). After the samples were exposed to sunlight for the day, they were transported back into the lab and subsamples were collected for analysis. Analyses will be done in Syracuse once I return to the US at the end of April. This is one limitation of field work in a remote location–we often do not know the results of our experiments until weeks to months after the field work is completed.
April 6, 2018. Up at 5:30 am and out on the water by 8:08 am! It was a beautiful morning for our first sampling trip.
We occupied six stations in total during our study–three outside the reef (OO, SO and CR), two within the reef (CR and BR) and one in the channel (CH) that drains much of the reef. To minimize the sampling time, we will occupy the reef and ocean sites on separate days. Today we sampled the three stations outside the reef.
The Crest Ocean site provides a great view of waves breaking over the crest and into the reef.
The total sampling time took about 2 hours, and we spent about 25 min at each sampling site. The first site was clear and shallow, perhaps 7 m and the bottom was covered with coral.
The SO and OO sites were much deeper, approximately 500 and 1300 m. The deepest station had a nitrogen-fixing trichodesmium present. At each station we deployed a light meter to determine how deep the ultraviolet and visible light penetrated. These are very important parameters needed to understand coral reef ecology.
April 4, 2018. After I arrived to Mo’orea on April 1st and got settled in, ate some lunch with the research team (more on that later), I had a “long winter’s nap” to recuperate from my long journey The next day we started to set up lab, coordinated plans for our field work, picked up researchers from the ferry and airport and searched for missing supplies. It will take a few days to set up and I am still waiting for the shipment of my supplies from Syracuse, which are currently clearing customs in Papeete, Tahiti.
For lunch we had sandwiches and some Remu vine with lime. Remu is an edible green algae that is a seasonal Tahitian delicacy sometimes called green caviar.
In the afternoon we were invited to join a group of students from the Victoria University of Wellington, New Zealand that evening for a traditional Tahitian feast (Ma’a) with food that was prepared in a natural rock oven built in the earth (Ahima’a).
Once the food was prepared it was presented to the gathering, and live Tahitian music played in the background as part of the feast. we danced after we ate and the music continued until late in the evening, and then at the end we thanked one another (no tatou — meaning for all of us) for the gathering.