Day-Night Study

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.

Marta putting the MET tower up
Marta securing the mircometeorological sensor (for wind speed, wind direction, and air temperature) before a late afternoon sampling excursion.  These data are needed to calculate sea-to-air gas fluxes.
Back from an early morning sampling trip - Copy
Back from the 0400 sampling excursion. L to R: Dave, Steph (behind Dave), Marta, (Pablo and Tony in the wheelhouse), Kristin (in foreground) and Rafel.
Celia working with the fluorometer - Copy
Celia measuring the optical properties (absorbance and fluorescence) of the dissolved organic matter in the seawater samples that we collected. The organic matter dissolved in the oceans is the main “sunscreen” that absorbs UV radiation in much of the world’s oceans.
Marta plumbing the filtration apparatus to collect a DNA sample for analysis - Copy
Marta preparing a filtering apparatus in preparation for collection of a metatranscriptomics sample. After the sample was filtered on site, the filter was flash frozen with dry ice on board the vessel.  The molecular tool known as metatranscriptomics basically tells us what microorganisms are present in the water (most of which we cannot grow in culture) and what they may be able to do (i.e., what genes do they have).  For example,  what microbes in the water have the capability to consume DMSP.
Steph filtering samples from an experiment she conducted to study nitrogen fixation in the coral reef. - Copy
Steph filtering samples from an experiment she conducted to examine nitrogen fixation in the water samples.

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:

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Thinking about the next sample, or just a good rest after a long night?

….but by the next day we’ve recovered:

Our fearless female posse the day after the diurnal study. Steph Marta and Celia at Tropical Gardens. Moorea. 4.22.18
Our fearless female posse the day after the diurnal study. Stephanie, Marta, and Celia.

Daily Sampling

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).

Syringe used to sample coral water
50 mL glass syringe used to sample right near the coral by a diver. The blue valve is closed after the sample is collected.
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Stephanie collecting coral water from the coral Pocillopora verucosa with the syringe.

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.

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An ISCA plate. Each well contains seawater with a known chemical. The chemical diffuses through the membrane into seawater and creates a chemical plume (or odor) that some motile bacteria respond to by moving towards the source inside the well.
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Deployment of the ISCA in the open ocean by Justin Seymour.
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Deployment of the ISCA on the sea bottom in a sandy area in the back reef.
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Deployment of the ISCA near the sea surface in the back reef.

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.

Boat at Gump dock. Sunny and cloudy - Copy
The juxtaposition of the clouds and sunny weather was beautiful. It rained about 30 min after I took this photo.
Recent Rain and Rainbow at Gump Station 3 - Copy
Beautiful rainbow after a recent shower. It is always humid and hot in Mo’orea!
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Mountains and clouds. Stunning views.
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Pick Hibiscus with mountains in the background.

Tetiaroa

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.

Leaving Moorea - Copy
Leaving Mo’orea

Lots of time on the way over for conversation and planning for our upcoming lecture and sampling in the Tetiaroa Atoll.

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Tetiaroa in the distance. Notice that the islands that comprise the Tetiaroa Atoll are flat unlike Mo’orea or Tahiti, which are quite mountainous.

There is only one entrance to the inside of the Atoll by water, and this entrance is for small boats only.

The only pass to enterthe atoll - Copy
The entrance is just to the left of the concrete platform. There coral crest can be seen on both sides if the concrete structure, except to the small pass on the left of platform. You can see a chain link across the entrance that need to be lowered before you can enter. Supplies and food for the hotel and staff are craned over from a large ship to smaller boats waiting on the other side.

Once you’re inside the atoll, the scenery is beautiful at every turn.

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View inside the Atoll.

Of course we consider ourselves very lucky to have the oceans as our laboratory.

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Inside the atoll. L to R: Miguel, Rafel, Pablo and Dave. We love oceanography.

 

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.

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Dave on bike near airstrip.

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.

Pablo checking the computers recording data from thye underway instruments - Copy
Pablo checking the computers that compile data from the seawater flow through instruments (connected to green tubing to the right of the photo).  These instruments allowed us to measure continuously several parameters just below the sea surface.  Parameters that were quantified included  temperature, particle light scattering, phycoerythrin, and chlorophyll (the main pigment associated with photosynthesis in most algae and plants).

The freshwater lake that we sampled was used by fishermen for centuries as  a source of drinking water.

Rafel and Miguel sampling freshwater pond - Copy
Miguel (foreground) and Rafel sampling the freshwater lake.
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Dave sampling in the main lagoon at Tetiaroa.
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Sampling outside of the Atoll. You can see the reef crest in the background–where the waves are breaking.

Some birds that we saw in Tetiaroa included:

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A Black Noddy
Brown Booby - Copy
Brown Booby
Frigatebird - Copy
Frigatebird

Sunlight-Mediated Chemistry

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.

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Far away view of the area where biological and photochemical experiments are conducted.
Location of water bath for photochemistry - Copy
Closer view of where our biological and photochemical incubations are conducted.
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Picture of the seawater water bath containing the quartz tubes, dark controls, the chemical light meters (actimoneters), and a thermometer. The water bath temperature is approximately 30 oC, which is the temperature of the seawater in Cook’s Bay–it’s bathwater temperature!

First Sampling

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.

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First sampling trip from Gump. From left to right: Kristin, Rafel, Marta, Pablo, Celia and Dave

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.

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Sampling stations: OO, Open Ocean; SO, Shelf Ocean; CO, Crest Ocean; CR, Reef Crest; Back Reef; CH, Channel.

The Crest Ocean site provides a great view of waves breaking over the crest and into the reef.

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Wave breaking over the reef crest. View from the crest ocean station.

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.

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Mo’orea coral reef. Photo by Stephanie (Steph) Gardner.

 

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.

Rafel and Pable deploying the light meter 2
Rafel (left) and Pablo deploying light meter.

 

Hima’a – Ma’a Tahitian Feast

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.

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Remu with lime juice

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).

Dave and Rafel in front of the Ahima'a 4.2.18 2
Dave and Rafel standing behind a 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.

4.3.18 Presentation of the Ahima'a for the Ma'a Tahiti 2
Hinano presenting the ahima’a tero (food) to the gathering

The Journey Begins

April 1, 2018. After 20+ hours in planes and airports, I am very happy to have arrived to the Gump Research Station on the island of Mo’orea in French Polynesia. It is quite warm (for me anyway) with daytime temperatures in the mid to high 80s (~35 oC). I have a wonderful view of the surrounding hillside and Cook’s Bay. We’ll do most of our work in the Bay both within and beyond the coral reef. For today and tomorrow we’ll be busy setting up the lab and organizing for all of the boat trips we’ll be taking in the coming days to collect samples and make lots of measurements — more on that later.

View from my Gump Station Apartment 4.2.18
View from Gump Research Station apartment.  Cook’s Bay in the background.  Papaya Trees in the hillside grassy area.