A better late than never post for #NF1802, Dr. Stukel #ontheblog

Stukel sets up the satellite-tracker inside the buoys

Although NF1802 has come to an end, we will continue to post for the rest of the summer! Stay tuned!

Today, Dr. Mike Stukel joins us once again on the blog! Mike is an Assistant Professor at Florida State University and one of the PIs on our joint NOAA RESTORE Science project. His PhD students, Tom and Taylor joined him in this survey.


“I study the intersection of plankton ecology and biogeochemistry.  I have a fascination for all of the microscopic critters (plankton) that drift constantly with the currents of the open ocean.  Much of my research focuses on either the role of plankton in converting carbon dioxide to organic matter and then storing that organic matter in the deep ocean (a process referred to as the biological pump) or determining how changes in the planktonic ecosystem affect the availability of prey for fish and other large organisms. During this project, my research goal is to understand how biogeochemical and ecological interactions at the base of the food web affect the survival of larval tuna.

The golden tufts in the bottom left are Trichodesmium, the long organism in the middle is a chaetognath, and many of the out-of-focus blobs are copepods

Specifically, I'm interested in two questions:

1. What processes supply nutrients to the algae at the base of the food web (upwelling that introduces deep nutrients to the surface ocean or nitrogen fixation that converts abundant nitrogen gas into plankton fuel)?  
2. How does the structure of the planktonic food web affect the efficiency with which primary production is converted to zooplankton biomass (i.e. fish food)?  

Illustration by Sabine and Baxter

On this cruise, one of my lab’s goals is to make simultaneous measurements of nitrate uptake and nitrogen fixation in tuna spawning habitat."

Mike looks for microscopic organisms in between stations

Stukel and the team during sediment trap operations on the back-deck

If you are a teacher or student and want to learn more about plankton, check out Mike's lab's website and this link and has lesson plan too!) developed by Ms. Colleen Miks.

Featured Scientist: Karen Selph

Karen in the lab-van whispering to the flow cytometer!

Hello blog, today Dr. Karen Selph from the University of Hawaii at Manoa shares some of her expert insight into the nutrient-limited world! Karen shared with the blog just a few of the multiple experiments she carried out while on board the NOAA Ship Nancy Foster during NF1704 as part of our NOAA RESTORE project. Karen’s main focus was collecting phytoplankton to analyze with a “flow cytometer” – a machine that tells us how many phytoplankton are out there and gives us a rough idea of their types.

In addition, she measured water column light levels used for photosynthesis by phytoplankton with a photosynthetically-active radiation (PAR) sensor that was attached to the CTD rosette. Karen shared with the blog: "The 6 casts that we performed will yield invaluable information on the light regime during the cruise." 

"The nutrient limiting phytoplankton growth in the Gulf of Mexico is nitrogen.  Nitrogen has many forms, and most phytoplankton can only use reduced inorganic forms (e.g., nitrate (NO₃), ammonium (NH₄)).  However, some phytoplankton can use nitrogen gas (N₂), which is in abundant supply.  This is quite a trick, as the chemistry involved is anaerobic (no or low oxygen) and phytoplankton produce oxygen! 

Karen and Lucy carry out one of the PAR casts

On this cruise, we collected many samples to figure out which of the larger nitrogen-fixing organisms that might be present – in particular, Trichodesmium (usually a bane to those who study zooplankton, as it can clog their nets!!).   Additionally, to assess the base line N-isotopic value for Trichodesmium, we collected samples for stable nitrogen isotope analyses.  We even analyzed a sample of Sargassum to figure out its isotopic signature with respect to the other nitrogen-fixing players in the GOM.  Once we get back to the lab, we will also examine our samples under the microscope looking for the presence of other nitrogen-fixers – some diatoms and other species harbor symbionts capable of this remarkable feat!"

The dynamic duo, Tom and Karen processed hundreds of samples during the survey

Shaun, Karen's travel companion, makes some new friends

Featured Scientist: Michael Landry

As we wrap up this year's survey, the first of two annual research surveys in the Gulf of Mexico for the NOAA RESTORE Act Science Program, we'd like you to get to know the PI from Scripps Institution of Oceanography, Professor Mike Landry! Read on as he describes his research and our cruise goals in his own words!

"I am a biological oceanographer. I have been on many ocean research expeditions over the years (since the 1970s), but never on a cruise in the Gulf of Mexico, never on a NOAA ship and never with fisheries scientists trying to understand a specific fisheries-related problem. So this particular cruise is special and a new learning experience in many respects. At the same time, it is also familiar. What we have investigated on past expeditions is how plankton food webs in different areas of the oceans function under different environmental conditions in order to understand the “rules” of why systems vary and how they respond to change. Our hope in this project is to apply the techniques that we have developed and the results from past experiences to characterize the unique aspects of the Gulf of Mexico habitat that lead to rapid growth and success of larval bluefin tuna (why do momma tunas migrate vast distances to spawn in only few small places in the ocean?) so that fisheries scientists might be better able to predict how they might be affected by future ocean changes.

Above: Groups of water bottles to
be sent to different depths
Below: Our filtration set up -
6 bottles at once!

"In this project, we are taking two approaches to studying food-web relationship and rates. One is experimental, involving direct measurements of community composition, productivity and nutrient uptake by phytoplankton, the microscopic plants of the sea. We also measure the consumption (grazing) of phytoplankton by zooplankton, the slightly larger but still pretty small protozoa and small animals that comprise the first 2-3 steps of the ocean food web. This is the “what is there,” "what are they doing,” and “how fast are they doing it” part of the study. Phytoplankton often go through one or two generations (cell divisions) per day, and they get eaten almost as fast as as they divide, so the tricky part of these experiments is separating the two rates (production growth and grazing loss) that are going on at the same time. We have a technique for this, which involves dilution of the grazing impact (using filtered water, changing the encounter frequency of predators and prey) in some of our experimental bottles. It is also important that we run our experiments under natural conditions of underwater light and temperature, so all of our experimental bottles that contain the plankton that we collected at different depths are put in net bags and attached at same depth to a line underneath a free-floating drifter float that we track by satellite for a day before picking up and exchanging bottles for a new batch of experiments. After a lot of filtering, preservation or freezing, and later analysis in our lab on shore, we should have a pretty good picture of how productivity and nutrients are moving through various routes in the food web to get to the specific zooplankton prey that bluefin tuna larvae like to eat.

Tom (L) and Mike (R) attach bottles to the sediment trap array

Mike (L) and Aki (R) hunt for BFT using microscopes onboard

"In the second approach to this study, we will use the tuna larvae themselves to tell us where they reside in the food web and what is the main source of nutrients (nitrogen) for primary production. This information resides in the nitrogen isotopic composition of the amino acids that make up the proteins of the tuna larva muscle tissue, which varies with the source of nitrogen (N2 gas for nitrogen fixation versus nitrate from deep water upwelling) and the number of predator-prey steps that the nitrogen has taken to get to the larvae, starting from phytoplankton. This sounds complicated, but the isotope analysis is easier to do than all of the experiments that are needed to assemble the food-web picture. One of our goals is to see if results from these two approaches agree, which has never been done before for any system because the isotope approach is so new. If this works out, it would validate using the isotopes in future studies, or also to look at changes in food-web structure and nitrogen sources that may have already occurred with climate change, using the muscle tissues of fish samples that have been taken in the past and preserved in museum collections."

Featured Scientist: Rachel Thomas

Today on the blog, we have a guest post from Rachel Thomas, learn about her research objectives during this survey in the Gulf of Mexico!

Rachel takes the CTD down to 2500m in the Gulf of Mexico!

My name is Rachel Thomas and I’m a PhD student at Florida State University studying the marine nitrogen cycle with the Knapp Lab.

Filtering sea water

On this cruise, I am looking at the concentrations of nitrate, a nutrient required by primary producers, found in the upper 300 meters of the water column. Water samples are prepared using a colorimetric technique that will turn the water varying degrees of pink, depending on concentration, and analyzed at a certain wavelength. I am also collecting water samples from various depths ranging from a depth of 2500 meters and 3 meters below the surface. These samples will be taken back to FSU where we will look at the different nitrogen isotope signatures found in the water parcel.

Rachel examines nitrate concentrations

Think of an isotope signature as a fingerprint, where each source of nitrogen has its own unique fingerprint. By comparing the known signatures of each source to our water parcel, we will be able to determine where the nitrogen is coming from.

Collecting water from the CTD rosette 

It is important to understand where these nutrients are coming from to fuel primary producers in order to better understand how changes in nutrient sources will affect the GOM productivity.