LSU biological sciences graduate student Mike Henson recently conducted field research in the great big blue! Mike works in Dr. Cameron Thrash's lab. We asked him to tell us more about his field experience at sea below. Enjoy!
Waves stretch far into the horizon. The sun’s rays pierce the crystal clear blue water. The ocean here gives no hints about its oxygen-less waters beneath its depths. Yet, about 100 miles west of Manzanillo, Mexico in the Eastern Northern Tropical Pacific is one of largest anoxic bodies of water, or oxygen minimum zones (OMZ), in Earth’s oceans.
OMZs form when nutrient rich bottom waters from the Pacific Ocean are brought up to the surface, causing large blooms or growth explosions of photosynthetic algae. As the algae begin to die, other microscopic organisms (or backterioplankton) in the water consume oxygen to metabolize organic matter produced by the algal cells. Once you reach 100 meters below the surface, oxygen levels begin to decrease. At 300 meters, the oxygen has been completely consumed. Any organisms such as fish passing through these areas that are incapable of living without oxygen will die unless they can escape to the more oxygenated surface waters.
This may sound familiar to many Louisianans. However, unlike the hypoxia (a.k.a. the “dead zone”) that occurs seasonally in the Gulf of Mexico from nutrient pollution, this naturally occurring oxygen minimum zone is present year-round.
In the Thrash lab, we study the microbiology of northern Gulf of Mexico hypoxia. We are also collaborating with Chief Scientist Dr. Frank Stewart of the Georgia Institute of Technology, who has National Science Foundation funding to study the oxygen minimum zone in the Eastern Northern Tropical Pacific. Scientists from eight different countries, including USA, Canada, Mexico, Iceland, Denmark, Austria, Spain, and Germany, myself included, recently spent three weeks aboard the R/V Oceanus collecting water and sediment to elucidate the organisms and processes involved in forming this peculiar area of the ocean.
LSU College of Science: What research questions were you trying to answer with your field research?
Mike: Bacteria are the unseen agents of nutrient cycling throughout the Earth’s oceans and in oxygen minimum zones. Understanding these organisms’ metabolisms, or what they “eat,” will help us identify their role in essential nutrient cycles such as the conversion of nitrate to gaseous nitrogen. One of these organisms, Pelagibacter, is the most abundant free-living bacterium in the global ocean. Researchers recently found that this organism is highly abundant in oxygen minimum zones. Yet, despite its abundance, this OMZ-related Pelagibacter species has not been cultivated (or isolated in an environment and grown in a lab) and its role in nutrient cycling is still not fully understood.
My work on the R/V Oceanus aimed to cultivate this bacterium and others. The organisms cultivated from our experiments will be used to test hypotheses developed from molecular based approaches in the oxygen minimum zone.
LSU College of Science: What did you bring with you on the boat?
Mike: One of the most difficult aspects of culturing bacteria is keeping yourself from contaminating your samples. Our bodies and the surrounding environments (e.g. tables, walls, air!) are full of microorganisms unique to that area. To prevent contamination, we bring a large portable hood or air filter that has a HEPA filter and positive airflow (air flowing out at all times) to protect our samples from the outside environment and ourselves. We also bring gloves to wear to collect samples, ethanol and bleach to sterilize our working area, and sterile bottles to place the water into.
The other important item that we bring is the flow cytometer. This machine allows us to accurately count each free-living bacterial cell we capture in our samples to determine how many cells are found in a given milliliter of ocean water (around a million cells!)
LSU College of Science: What does it LOOK like to be in the field, for you? What do/did you eat, wear, etc.?
Mike: On the R/V Oceanus, a typical shift consisted of waking up at about 4 a.m. to help cast the first CTD. A CTD (conductivity, temperature, and density) is an instrument used to collect water at different depths and measure the water profile for things like salinity (salt concentration), light, temperature and oxygen concentrations. Depending on the depth, a cast could take anywhere from 45 minutes (down to 200 meters) to 4 hours (down to 2,500 meters).
During a day's work, we may perform 8-12 casts. In between each cast, you collect or help collect and process water. Water collection from the bottles on the CTD may take as long as two hours. One might think of the CTD as a watering hole. When the water arrives after a cast, the scientists surround it, waiting their turn to collect the water they need to run their experiments!
On the ship, the “dress code” is flexible besides close-toed shoes. You can wear what you felt is comfortable. This was usually pants or shorts, a t-shirt, and a hat. Having a good pair of shoes is essential. Water is constantly being filtered, dumped and splashed, so having shoes that dry easily and don’t get really smelly is key, for both yourself and your roommate! I like to bring my close-toed Keens. They dry easily and when they get wet, you don’t get foot rot like you do in regular shoes. Everyone has a shoe type they like to wear, just don’t wear tennis shoes. Oh, and I bring lots of sunscreen! We are often working long hours on the deck of the boat. The sun is bright and on a ship it is hard to escape it. Trust me, you don’t want to get burnt on day one of the trip.
Food on the ship is always good. We eat regular meals just like you would at home. On the R/V Oceanus we had two great chefs who made breakfast, lunch and dinner for us every day. Meals included pasta and meatballs, fresh-caught Wahoo, steak, eggplant parmesan, Cuban sandwiches, tacos with fresh guacamole, and much more. The chefs also always made great desserts! Okay, I’ll let you in on a little secret too: every ship has an ice cream stash. On the R.V Oceanus, it was back near the engine room, and it was full of ice cream, drumsticks, and ice cream sandwiches. Life isn’t too bad aboard these boats. :)
LSU College of Science: What is it like being "at sea" for extended periods of time? What do you like about it? What are the difficulties?
Mike: Being on the ocean for me is incredibly peaceful. When you are 100-300 miles off the coast, the waves stretch as far as you can see, your view of the horizon is unabated, and the only sounds are those of the birds flying around you and the activities taking place on the boat.
The boat is large, but it is often filled with equipment, lab space, etc. This means that there isn’t a large amount of space to just relax or be by yourself. So it's important to find that get-away space. On the R/V Oceanus, it was on the second level deck. There, you’d get out a deck chair and relax, listen to music, and enjoy the views. Many of the Master's students, PhD students, postdoctoral researchers and some of the faculty working on the ship would meet here, talk about life in their respective country, and nap.
During many of the evenings, we would meet in front of the bridge (where the boat is driven from) on a walkway that lets you sit high above the ship and watch the sunset. If you were lucky and there were no clouds in the sky, you can watch the green flash appear as the sun disappears below the horizon.
Some of the difficulties are being away from family and friends. Internet on the ship is limited and there is no cell service to call loved ones. While this can be a plus and minus, it is can tough. Having a good group is also important. You eat, sleep and drink with your fellow crew 24 hours per day, so a group that is respectful of space and time is important to keeping everyone happy.
LSU College of Science: What was your favorite part about this field experience? What was most challenging?
Mike: My favorite part about this field experience was being surrounded by incredible scientists. Being on a ship is a team effort, and everyone was incredibly supportive, making the time that much more enjoyable. I will always remember sitting out on the walkway overlooking the Pacific Ocean and watching every sunset and thinking how stunning each one was in its own unique way.
The most challenging part was cruise prep. Because this cruise left from a foreign country, extra time and effort was required for packing and shipping equipment, disposables and other items. You don’t realize how stressful it is to have to ship expensive lab equipment to a foreign country until you do it for the first time.
LSU College of Science: What's next?
Mike: I arrived back in lab on May 26. On the ship, I conducted four culturing experiments resulting in over 1,900 wells inoculated with roughly 1-3 bacterial cells each. The cells will incubate at 11°C (in situ temperature). This week (June 26), we will count the numbers of cells in each well to determine if the incubation resulted in growth. When the wells are positive, the cultures will be identified and, if of interest, used in experiments to test hypotheses generated from culture-independent studies in the Eastern Northern Tropical Pacific oxygen minimum zone.