My name is Rasmus Swalethorp and I am a postdoctoral researcher at Scripps Institution of Oceanography, UC San Diego. I am a biological oceanographer with a particular interest in the ecology of planktonic organisms. Up until now most of my research has been done in the Arctic and Antarctic and this was my first research cruise to the Gulf of Mexico.
Fishing for copepods in the sea ice in the Artic Ocean
Compared to the polar seas it was astounding to see the number of planktonic species that lived in the Gulf. While, I am used to only seeing about tens of different species of fish larvae or copepods (small planktonic crustaceans), in the Gulf I was amazed to see hundreds. This high species richness leads to very complex ecosystems that my colleagues and I are working hard to disentangle!
A lovely bluefin tuna (Thunnus thynnus) larvae collected during our survey
This is the second cruise aimed at understanding what makes up a good habitat for larval Bluefin tuna (BFT) to survive and grow. We want to be able to tell where to find these habitats and how much will be available in the future ocean. Much of my research has focused on baby fishes, the larval period of a fish’s life. This is the time when fish, are the most vulnerable to starvation and predation. Therefore, it is also considered to be the period most critical to recruitment: which is the number of fish that make it to adulthood and reproduce themselves someday. Understanding what is needed for a larval fish to survive is of particularly importance to management of commercially exploited fish such as Bluefin tuna.
After all what would the world be without sushi?
That’s where my expertise comes at play. I study what they eat. The more the larvae eat, the faster they can grow to improve their hunting capabilities and to avoid being eaten themselves. So, how do we determine a good larval tuna habitat? First, we need to know how much food is available to the larvae, and then which sources of nutrients are sustaining the food chain sustaining the larvae.
Mike L. and Ramus recover and rinse the ring-net
that has sampled the zooplankton (prey of BFT)
You may imagine that these guys are just little eating machines consuming everything available around them. But despite being ferocious predators, we have found that they are actually quite picky with what they eat. So to determine the availability of larval tuna “food,” we first need to figure out what the larvae are actually eating. This is done through meticulously by dissecting the tiny stomach and intestine of the larvae under a microscope to analyze their diet. As many of the prey are crustaceans, they are difficult to digest, (imagine digesting a crab with its shell, ouch!), so we can identify the species and size based on the undigested remains. By comparing this diet information with what is collected in our zooplankton nets we can see which zooplankton the larvae prefer to eat and how much food is available to them.
We are also studying their feeding habits by looking at their Nitrogen (N) signature. What is a Nitrogen signature? We look at the two naturally occurring isotopes of N (that is different variants of N). This is done in specific amino acids, the building blocks of proteins that make up the body tissues of the fish larvae. The less common 15N isotope is heavier than the common 14N. This weight difference means that 15N assimilated from the food is moved around the larval body and ultimately excreted as waste products at a slower speed relative to 14N. As a result there is a buildup of 15N compared to 14N in the larvae relative to their food.
Nitrogen atoms
Because we know the amount of 15N in the prey, and that the buildup increases at a constant rate for each level of the food chain, from algae to herbivorous zooplankton to carnivorous fish, we can determine how high up the food chain the larvae are.
Some larger zooplankton collected by our ring net
This method gives information on what the larvae have been feeding on the past days to weeks, while looking at the stomach contents only tells us what they have eaten over the last few hours. Also this method gives us clues on other potential preys, such as smaller unicellular protozooplankton that have soft bodies and are rapidly digested and therefore cannot be seen in the stomachs analyzed under the microscope. By looking at 15N we can also tell from where the N is coming from that is taken up by the algae at the bottom of the food chain. We can see this by looking at certain amino acids in the larval tuna where there is no buildup of 15N. Therefore, these amino acids reflects the composition of the N taken up by the algae so if e.g., there is very little 15N compared to 14N it means that the plants are taking up N2 from the atmosphere, and if there is more it means they are taking up Nitrate brought up from the deep.
I am now back in the lab and I can’t wait to start analyzing all the tuna larvae we collected to unravel the secrets of their diet.
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:
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)?
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.
Rachel filters water collected at 500 m in the GOM
Rachel Thomas from Florida State University's Earth Ocean and Atmospheric Sciences Department is a doctoral student in the Knapp Lab and she is our guest-blogger today sharing a bit of her research and cruise goals:
"My personal goal on this cruise is to be able to identify bluefin tuna through a microscope. I’ve never seen fish larvae before, so everything the “fish team” brings up in the nets is new and exciting to me! Most of my previous work is involved in the Southern Ocean, where there are unused nutrients in the surface ocean. This gives us a unique ability to look at how phytoplankton are reacting to different physiological stresses, such as light and nutrient availability."
One of these nutrients, is Nitrate (NO3) which is a form of dissolved inorganic nitrogen that is utilized by phytoplankton in the ocean (Malerba et al 2012). One of the aspects of our project (NF1704 & NF1802 is to examine the dynamics between these inorganic compounds at different depths of the surface water column (0-500 m).
Typical nitrate vertical profile comparison, (modified from A. Nahian Avro)
T. Kelly and Rachel Thomas recover the CTD rosette
"The Gulf of Mexico has a very different light regime compared to the Southern Ocean, and little to no nitrate in the surface waters. Our research team hopes to explore how these contrasts are expressed in the isotopic composition of subsurface nitrate in the Gulf of Mexico. We will also use the isotopic composition of subsurface nitrate in the Gulf of Mexico to understand the nutrient sources for primary productivity fueling bluefin tuna growth in surface waters."
Click here for last year's blog post from Rachel's experiences during NF1704.
A bit of trivia: the Southern Ocean is the fourth largest of the world's ocean basins and extends to Antarctica. Psst, how many oceans are there? (click here for an answer)
Rachel Thomas and Alanna Mnich ready to deploy an SVP drifter on the fan tail
Top: NOAA Shiptracker map of transit
around Florida
Bottom: Four NOAA Ships meet off the
Dry Tortugas!
Our survey started in Jacksonville, FL, and did a fun U-shaped track around the Florida Peninsula until we reached our study destination: the grand Gulf of Mexico. We even sailed past several other NOAA ships doing work in the area (NOAA Ship party!) to include the NOAA Ships Okeanos Explorer(EX), Oregon II(R2), and the Pisces(PI)! The NOAA Ships fleet support science in multiple fields including oceanographic, fisheries, and atmospheric research.
Join us for another adventure on NOAA Ship Nancy Foster!
It's been a week already, and we are now in the Northern Gulf of Mexico searching for the elusive bluefin tuna larvae. They have been hiding from us, but we are relentless and will keep searching! Our strategy is to target some favorable habitat which is usually in between oceanographic features.
I hope you learn something new during our journey and feel free to ask questions!
Scientists and crew sign the NF1703/04 NOAA Corps flag
First of all thank you for following our research expedition by reading our blog! My name is Estrella Malca and I was the chief scientist for this survey (NF1704) aboard the NOAA Ship Nancy Foster. What does that mean? Each project has a designated person that takes a leading role on the logistical, scientific and reporting aspect of the entire survey.
One last selfie!
Estrella (Chief Sci) and Samantha (Senior survey tech)
I love to figure out the 'tetris' of things, so this year's cruise has been challenging but fun! Why challenging? Well, usually we have 6 months+ to prepare for our surveys: buying equipment, supplies, assigning scientists and volunteers to participate, and most importantly, securing any relevant permits as well as communicating with the ship's officers and crew about the multiple operational aspects of our project at sea. However, because of our very recent NOAA RESTORE project selected for funding, we had just two months to get a brand new project planned, signed and delivered on time! Without the rest of the science team, there is no way we can come out here and successfully achieve all of our research goals and deliverables!
We had the pleasure to continue to collaborate with several of our partners and also obtained new research connections!
NF1704 Leg 1 scientists
NF1704 Leg 2 scientists
Estrella and Niki deploy our very last satellite tracked drifter
Here is a list of our NF1704 accomplishments!! We were quite busy this past month as you can see!
ü500++ Tunas collected, more than 600 specimens individually measured at sea
ü90 CTD casts: Depths were (300m, 500m, 1500m, and 2500m). The sensors we used on the CTD included temperature, oxygen, salinity, chlorophyll-a and CDOM, conductivity, PAR. üContinuous measurements of currents (ADCP) from Key West to Progreso and to Miami
üContinuous measurement of flow through (TSG) from Key West to Progreso and to Miami
ü136 net tows (25m): 120 Bongo-90 (240 jars) & 16 Mini-bongo net tows
ü16 Mesozooplankton and 16 microzooplankton samples
ü120 Live-sorted plankton samples ü95 specimens selected for genetic analysis * 40+ Open House attendees. Our outreach event welcomed our scientific counterparts, students, professors, and fishermen in Progresso, Mexico
We hope that our projects will fill in a lot of the gaps about the biogeochemical ecosystem in the Gulf of Mexico as it relates to bluefin tuna research for the Western Atlantic stock. Our results will be shared with local and regional stakeholders like NOAA, ICCAT, among others. Soon, we will get started working up the data! Stay tuned and read our posts!
Group selfie, navigating into to the port of Miami
Today’s post features LTJG Nikita "Niki" Norton, and officially welcomes her
to the FORCES Lab family! Niki is the current "Florida Bay Operations Officer," replacing LTJG
Aras Zygas. As a part of
the NOAA Commissioned Officer Corps, she operates sampling platforms to
facilitate scientific research and provides logistical and administrative
support to NOAA’s mission. She shared with the blog:
Niki records the flowmeter data into our logsheets
"For the last
three years, I was assigned to the NOAA Ship Bell M. Shimada out of Newport, Oregon, conducting fisheries surveys from
Vancouver, Canada all the way down to San Diego, CA. Along with the responsibilities of being
Navigation Officer and Medical Person in Charge, my primary duty was to
“drive” the 210’ Fisheries Survey Vessel every day for 200+ days a year
Niki and Loni on the back deck, waiting to deploy the CTD
"Many of the sampling techniques that are routinely performed
by research groups on the West Coast to collect plankton are exactly the same
as those conducted by the FORCES lab to collect larval fish!
"This included
Bongos, Neustons, MOCNESS, and CTDs on many of the projects. We performed extensive mid-water stern
trawls with a net the size of a football field to catch fish like Pacific hake
and sardine. We followed and tagged endangered Resident Killer Whale pods and
acoustically monitored beaked whales at 4000m depth. The remainder of the year, the ship completed Remotely Operated Vehicle (ROV) transects and hydrographic missions in the Farallons and Channel Islands.
Niki and Estrella deploy a satellite tracked drifter
"While many of the operations may be the same, this new job
with the Southeast Fisheries Science Center is quite different - as is the
scenery! Rather than the whipping cold
wind of the Pacific Northwest, the hot sun in the Caribbean and Gulf of Mexico
is one of my favorite parts of the job. With the FORCES Lab, I get to work "on deck" to deploy and recover gear, wash down nets, assist with station planning, and see the plankton and water samples we catch up close!
NOAA Ship Nancy Foster, Brewers Bay, USVI
"When I am not underway as a
scientist, I work in the office to ensure that the lab has everything they
need logistically to sail each year by assisting with cruise planning and administrative
budgeting. Now that the first year of
sampling has come to a close, I am very excited to see what new projects I will get to be a part of and hope to use my background in reef fish ecology
and microbiology to explore new research with the FORCES lab – while getting ready
for next year!"
Girl Power! The women behind the science in NF1703!
Top (L-R): Sarah H., Niki, Trika, Sarah P.
Bottom (L-R): Kristen, Vanessa, Jess, Alexis
Before we return back to our corresponding labs, and start to process our samples, we have one more post from one of our collaborators! Dr. Bob Arnone was part of the land-support team which guided our survey with satellite updates and oceanographic analyses of daily conditions. The GOM is a very large and dynamic ecosystem and we can use all the help we can get! Bob and two post-doctoral researchers (Brooke Jones and Inia Soto) prepared a blog post to share some of their work at the University of Southern Mississippi. I hope you enjoy it and next year, we encourage our collaborators to do joint posts like this one to share their land based work as well!
Robert Arnone and Brooke Jones in the OWX showing the cruise track
of the Nancy Foster in the Gulf of Mexico and the daily ocean conditions
"We are Prof. Robert Arnone, Dr. Brooke Jones, and Dr. Inia Soto from the University of Southern Mississippi, Division of Marine Science, Stennis Space Center. Our Ocean Weather Laboratory (OWX) was able to work with the researchers aboard the Nancy Foster during the RESTORE Bluefin tuna survey (NF1704) this past May and early June 2017. We provided daily updates on relevant ocean conditions while we followed the ship's cruise track as well as abnormal conditions that might affect the research results. Many of the ocean products we provided are new, and working with the Foster cruise allowed us to compare the observations from our lab with ship observations. Our goal is to demonstrate that our daily ocean products can provide the Foster a better understanding of sampling for Bluefin tuna. We want to continue to work with the research group to optimize our products and the packages we provide.
"The OWX Laboratory was established to characterize the daily ocean conditions and abnormal events in the Gulf of Mexico. Our focus is to assemble products from satellite remote sensing ocean color data, sea surface temperature, and several physical ocean circulation models to define ongoing ocean activity. Our daily products include the ocean bio-optical properties of chlorophyll-a, turbidity, water clarity, phytoplankton absorption, and particle back-scattering and physical oceanographic conditions (temperature, salinity, currents, mixed layer depth). The OWX Laboratory research is focused on the understanding of the interactions between the oceanographic conditions and the ecosystem. New OWX products also include weekly dynamic "anomalies" which can help us identify abnormal physical or biological conditions that are occurring so possible bio-physical oceanographic events can be identified in the Gulf of Mexico.
The Ocean Weather Laboratory at USM with various screens visually monitoring ocean conditions using Google Earth
"The daily OWX Laboratory products provided locations to the Foster for adaptive sampling to help support optimum data collection and understand how Bluefin tuna are responding to changing bio-physical conditions, as well as identify events such as harmful algal blooms, flooding events, coral reef mortality, and others that may be occurring in the Gulf of Mexico.
"The OWX Laboratory visually displays animated ocean properties in several monitors using Google Earth. These tools provide capability to integrate ship tracks and observed data with satellite and model data so we can coordinate with ship operations.
"The videos below show Google Earth animations of the OWX Lab's animated daily products of the nowcast bio-physical processes (Chlorophyll, currents, and salinity) and the dynamic abnormal ocean conditions with the ship track for the Nancy Foster Bluefin tuna survey for the week (May 22-27, 2017)."
We love to share our collaborators' research, especially when the OWX Lab's main focus is to provide new capabilities for ship sampling so that optimum data can be collected and related to the changing ocean conditions. We hope that the daily OWX products can be used for fisheries applications very soon!
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
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."
Today we learn about Tom who shares his insights into the infamous sediment trap! Here is his blog post. (Read previous guest posts here!)
Tom and the incubation system
My name is Thomas Kelly and I am a PhD Candidate at Florida
State University in the Plankton Ecology and Biogeochemistry Lab. One of the
principal tools that I use in my research is called a sediment trap. A sediment trap collects marine particles and
organisms as they sink through the water column. You can think of a sediment
trap as an underwater rain gauge that collects sinking plankton instead of
falling rain drops.
Since most of the biological growth occurs where light is
plentiful (i.e. photosynthesis), the majority of marine organisms live within
the surface layers of the oceans. But as these organisms die, get broken up, or
defecate, particles settle out of the surface layer and into the deeper ocean.
Our sediment traps are placed in between these layers and can tell us about
what kind and how quickly carbon, nutrients, and other material leaves the
surface ecosystem.
Tom and Mike deploy the sediment trap
The deployment of the sediment trap is really quite straightforward and will typically take a bit over an hour. The whole assembly consists of a long rope that extends from the surface all the way down to the depth of the last sediment trap frame (Pictured to the left), about 650 (210m) feet. At the bottom we place 60 lbs (27 kg) of weights and at the top a set of buoys. For the Bluefin Tuna Cruise the sediment trap frames are placed at approximately 150, 400, and 600ft (50, 120, and 200m) of water depth so that we can measure how the sinking of particles changes with depth.
Onto the frame we attach a set of tubes filled with extra
salty seawater so that any particles that sink into them will stay in the tube
rather than being mixed out again (the denser fluid will stay inside the tube
just like a glass of water will stay inside a cup). Besides that, the tubes are
also spiked with formaldehyde to kill anything that tries to eat the sinking
material and a baffle at the top to reduce turbulence around the top of the
tube.
Tom plots his next filtration experiment
After 3-5 days of drifting, the sediment trap is ready to
come aboard and be processed. In general, each of the sampling tubes is
filtered and frozen for later processing on land where we can look at such
things as the carbon and nitrogen content. Some of the specialized aspects that
we can look at from the sediment traps include the size classes of the
particles collected, the source of the material collected, and the quantity of
various metals and nutrients within the material. Ultimately the sediment trap
provides invaluable information about how the ecosystem looses energy and
material to the deeper water column.
Today's featured scientist is a recent graduate from University of California - San Diego, Jennifer Beatty! She is a research assistant at the Scripps Institution of Oceanography. Read on to find out her goals for this survey in her own words!
Jennifer fixes a sample collected in the GOM
"The lab I'm involved with studies the interaction of phytoplankton and zooplankton, which are the lowest levels of marine food webs. Phytoplankton are essentially the plants of the sea, while zooplankton are the animal plankton that eat them. The way these two interact changes in different parts of the ocean, which impacts the dynamics of organisms further up the food web, including bluefin tuna larvae! During this cruise, we are hoping to get an idea of what is happening at these lower food web levels to illuminate what conditions are optimal for larval bluefin tuna.
Processing the ring net in the wetlab
"My
primary goal for this cruise is to gain field experience at sea. I've worked with
samples in the lab, but I wanted to see where they come from and how
they are collected. Additionally, I wanted to taste what research at sea
is like because I plan to pursue a graduate degree in marine science.
Before I head there, I'd like to have a better idea if I prefer research
dependent on field work or prefer to stay in the lab."
