Tiny Fishes from the Deep – Rebecca Asch

Petri dish full of mesopelagic fishes caught in the MOCNESS.  Organisms marked with yellow stars are Cyclothone; fish marked with red stars are myctophids, and; the fish marked with green stars is a rather beat up hatchetfish.  Note that not all Cyclothone, myctophids, and hatchetfishes shown in this picture are marked.

Those of you who are regular readers of this blog will know that one of the key foci of this research cruise is to develop a greater understanding of how the biological pump functions.  The biological pump refers to a set of processes in which atmospheric CO2 enters the ocean and is taken up by phytoplankton during photosynthesis and then converted to organic matter.  If this organic matter is transported to depth quick enough, it will be “sequestered” there, meaning that it will stay at depth and won’t return to the surface ocean where the organic carbon can be remineralized and converted back into CO2, which can in turn contribute to global warming. 

It is hypothesized that certain fishes may contribute to the biological pump.  More specifically, the fishes that may affect this process are mesopelagic fishes that generally live at depths between 200-1,000 m.  Many of these fishes participate in diel vertical migration (DVM), in which they hang out at deeper depths during daylight hours but then travel to surface waters at night to feed on organisms found there.  By eating at the surface, but respiring and pooping at depth, these fishes may serve as a vector for carrying organic carbon to deeper into the water column. 

During this cruise, I’m conducting research to explore this hypothesis.  We are collecting mesopelagic fishes at both and night with a MOCNESS net.  MOCNESS stands for Multiple Opening/Closing Net and Environmental Sensing System.  The MOCNESS can collect zooplankton and fishes from 10 discrete depths during a single deployment, allowing us to better understand the depth range inhabited by particular organisms.  After the cruise, I plan to identify the fishes collected to species, dissect them removing their stomachs, and then measure the total organic carbon in their gut contents.  By doing this, we will be able to see how much of the food eaten by these fishes at the surface makes its way down to depth.  This will provide us with some initial information about these fish’s potential contribution to the biological pump.

Some of the mesopelagic fishes that we are sampling have a fairly cosmopolitan distribution and are found across wide swathes of the Pacific Ocean.  However, one notable pattern that we see at Station ALOHA is that the mesopelagic fishes found here are tinier than those in many other regions.  This is noteworthy because most mesopelagic fishes are not very big to begin with.  Typically, sizes are 2-10 cm, whereas on this cruise we are capturing fish at the smallest end of this range.  This reflects the fact that the area around Station ALOHA has relatively little nutrients.  When nutrients are scarce, smaller sized phytoplankton tend to be more competitive.  These small phytoplankton are eaten by small grazers, which are in turn consumed by small fishes.  As a result, the whole ecosystem is miniaturized.

Below are some “fun facts” about common fishes found in the mesopelagic realm of the ocean:

Cyclothone spp. These fishes, whose common name is the bristlemouths, are the most abundant type of vertebrate on planet Earth.  They have an elongate body and a large mouth relative to their body size.  Having large mouths is fairly common mesopelagic and deep-sea fishes.  This is because such fishes live in environments with relatively little food.  By having a large mouth, these fishes can capture food of a variety of sizes, allowing them to eat whatever sized meal they encounter. 

Another characteristic of Cyclothone that is shared among other mesopelagic fishes is that their body is covered with photophores.  Photopores are light producing cells.  Photophores can help fishes camouflage with their environment by mimicking downwelling light from the sun.  This is why Cyclothone and many other mesopelagic fishes have their photophores concentrated on their belly.  That way they won’t be easily seen by predators looking up at them from below.  Among some mesopelagic organisms, photophores can also be used to detect and capture prey and may be involved in attracting mates. 

Talking about mating, an interesting aspect of the life cycle of some fishes in the genus Cyclothone is that they are protandrous hermaphrodites.  That is a technical way of saying that these fishes start off life as males but, as they grow, they will switch sexes and become females.  This life history characteristic is common among many fishes, including clownfishes, which are the fish that Finding Nemo is modeled off of.

Myctophids. Myctophids are the second most common group of fishes that we have been sampling during this research cruise.  Their common name is the lanternfish, because, like Cyclothone, myctophids also have photophores that can produce bioluminescent light.  Myctophids are an incredibly diverse family of fishes, with ~250 species found worldwide.  Most myctophid species engage in DVM.  As a result, they possess a variety of adaptations to help them migrate between the mesopelagic ocean and the surface.  These adaptations include having a more muscular body than many other deep-sea fishes.  Their swim bladder is filled with fat to increase their buoyancy and reduce the energetic cost of migrating to the surface.  Lastly, they have adapted to tolerate the broad range of temperatures that they encounter along their migration route.  Although myctophids do not grow to be very big in size, there are fisheries that catch them in some parts of the world.

Hatchetfishes. We have caught a few hatchetfishes during this cruise, but they only seem to be captured in a few depths fished by the MOCNESS net.  This may reflect the fact that most hatchet fishes do not engage in DVM, so they may be more limited to inhabit a narrower range of depths.  Hatchetfishes have a particularly distinct body shape.  Their body is compressed side-to-side, but their body is rather deep when looked at dorsoventrally.  Their sides tend to be silvery and covered with photophores.  Their silvery color helps them blend in with their environment, making them harder for predators to detect.  Most hatchetfishes have a short gut, which is indicative of a carnivorous diet.  They are also characterized by upward pointing eyes and an upward pointing mouth, which allow them to better hunt organisms found above them in the water column.  Some fishes in the hatchetfish family have two sets of retina and lens in each eye, allowing to both look upward and sideways without moving their head. 

So far we have only deployed the MOCNESS net during the day.  We have a bunch of nighttime deployments coming up, so we will likely see new things in the coming days.  Stay tuned!

Me with the MOCNESS net in all of its glory.

How many Tums are in the ocean? – Adam Subhas


A planktic foraminifera, species G. ruber.  This foraminifera is about 0.3 mm across, with spines that extend another 1 mm or so.  Both the shell and the spines are made of calcite, a form of calcium carbonate.  Foraminifera are animals, and must hunt their food.  Here it has caught a shrimp in its spines — a tasty lunch!  Image credit: A. Subhas and S. Oron

Heartburn, or acid reflux, has a common and simple remedy: take antacid tablets, which dissolve in your stomach and neutralize excess acid.  You may be asking yourself: what does this have to do with the ocean?  In fact, the ocean as a system uses antacids in exactly the same way.

Many marine organisms grow calcium carbonate shells, the active ingredient in TUMS.  These shells make up the basis of limestone rocks, and are abundant all over the world, and on the ocean floor.  The white cliffs of dover are made up of the “liths” of tiny algae known as coccolithophores; the pyramids of Giza were built with rocks chock-full of calcifying organisms known as foraminifera.

These rocks all got their start with microorganisms growing in the surface of the ocean, those organisms dying, and their shells settling to the ocean floor. As the world oceans become more acidic due to fossil fuel burning, these shells — the TUMS of the ocean — will dissolve back into seawater to neutralize the excess acid. I study this cycle of calcium carbonate formation and dissolution in the ocean, and how it regulates the ability of the ocean to take up and release CO2.

One fun fact: The ocean holds 60 times more carbon in it than the atmosphere does.  This is because of the large buffering capacity of seawater, which is regulated by the formation and dissolution of calcium carbonate shells in the ocean.  The amount of buffering capacity, or alkalinity, in the ocean, is equivalent to about 200 billion billion dissolved TUMS tablets — yes, that’s right, two times ten to the power of 20 TUMS tablets.  And yet — even with all of that buffering capacity, we are still changing ocean pH by burning fossil fuels.

On this cruise, I am collaborating with my colleague, B.B. Cael, to test how adding alkalinity will affect organisms growing in the open ocean.  Depending on what we find, we will better understand how alkalinity affects the growth of marine organisms and their shells.  With enough research and experimentation, we may be able to add more alkalinity to the ocean to help counteract global warming and ocean acidification.

I am also studying the role the enzyme Carbonic Anhydrase plays in the formation and dissolution of organisms’ shells. This enzyme drastically speeds up reactions crucial for both calcification and calcium carbonate dissolution.  For instance, pteropods grow calcium carbonate shells, but also produce a lot of carbonic anhydrase.  Pteropod shells are abundant in the surface ocean, but dissolve very quickly once the organisms die.  It is possible that carbonic anhydrase is catalyzing this dissolution reaction, and I hope to measure enzyme activity to link its presence to this dissolution reaction.


Volume of the oceans: 1.332 billion cubic km = 1.332e21 cubic dm, dens is 1.025 kg/dm3, alk = 0.0022 eq/kg, mass of caco3 in tums is 0.75g, or 0.015 eq alk per tablet, so we get 2.0e20 tums tablets in the ocean

How this training cruise is impacting early career scientists and the future of oceanographic field research – Matthew Rau


A research cruise is quite an operation. Speaking as someone who is fairly new to oceanographic field research, it is amazing how much planning, coordination, logistics, and manhours were necessary to fill the Kilo Moana with scientists and equipment to get us all out to sea for a ten days of research. Training to carry out this sort of planning is not something you typically get early in your career (if ever). As scientists, even early-career scientists, we’ve all become pretty skillful at asking relevant and important scientific questions. How we answer those questions is a whole different story. The ocean is big, dynamic, and complicated. Many of the most important questions we have about our oceans’ function and health cannot be studied remotely. The answer? Conduct field research on a cruise. The only problem is that proposing, planning, and implementing a research cruise is far from simple.

In general, research takes a lot of planning. Ideally, your preparation will help ensure that your efforts test your scientific hypotheses and yield valuable new scientific knowledge. I typically work in a lab. Planning experiments takes a lot of work and consideration. Planning a research cruise takes this to a whole new level. Not only must you plan your own sampling and measurements, but you also must decide what kind of ship best suits your science needs, when and where to go to answer your hypotheses, coordinate the science plans of the other scientists, and logistically determine how everything will be safely managed on board. And we haven’t even considered the ship yet. Who will crew your vessel while you conduct your research? What kind of cables, winches, cranes, and other ship-board equipment will you need? What is the safest way to deploy that new instrument you just acquired? Luckily, the University-National Oceanographic Laboratory System (UNOLS) is there to handle the bulk of the actual ship management, but training young scientists on how best to manage these resources is still important to ensure their effective use in future oceanographic research.

This training cruise is meant to do just that. Myself and the other participants are getting a behind-the-scenes look at what goes into cruise planning and management so that we can lead future research at sea. This cruise has already been an invaluable experience and it is hard to imagine taking on the role of a chief scientist aboard a research vessel without this exposure. As oceanographers and marine scientists, we are incredibly lucky to have these scientific facilities available to our research and experiences like this will help ensure we know how to use them!

The most important aspects of cruise planning – Katherine Heal


It’s easy to get caught up in the pace of sea going operations and not recognize all of the work it takes to plan and prepare for a cruise. Of course there is the proposal writing and requesting ship time through UNOLS. Then there is the ordering of equipment, the shipping, the permits, and a myriad of other logistical steps necessary to make an operation like this happen. After deploying a free floating array at 4 am this morning (pictured), Tara Clemente and Matt Church shared their thoughts with me on important aspects to cruise planning. Combined, Tara and Matt have served as chief scientists on somewhere in the order of 40 cruises, so I figured their insight into the matter was worth sharing. They landed on two main pieces of advice, communication and managing resources. Communication-wise, both agreed that having clear overarching goals for the cruise while balancing individual objectives were key for setting the stage for making making the most of our time at sea. They advocated for having clear lines of communication to the captain as well as the land- and sea-based marine technicians and starting those conversations early. The second aspect of managing resources is more obvious to me – as a team of scientists moving aboard a ship, we have to think carefully about the dance to get the right equipment, deck space, wires, and time to make this all come together. This involves being aware of each piece of equipment, having a clear vision of where and how it will be deployed, and recognizing the time each effort will take. Sitting in the staging bay after a full night of successful operations (ahead of schedule!), I can easily say that being prepared pays off.

The beating heart of the ocean – Nick Hawco

Caption: Left) A surface ocean phytoplankton, Trichodesmium. Right) The remains of surface ocean phytoplankton: a particle sinking to the deep ocean. Taken by the Scripps Plankton Recorder. Photo credit: Jaffe Lab, Eric Orenstein

The heart wants what it wants, but what it wants most is to pump. The thump thump squeeze of atria and ventricles pass blood fresh with oxygen into arteries, organs, cells.

Out here, in the heart of the sea, the ocean wants to pump too. This one, though, is a bit harder to see or hear. I’ll explain: the ocean creates a habitat for microscopic phytoplankton at the sea surface, where a miraculous reaction takes place: sunlight and air transforms into stuff. Specifically, phytoplankton capture light energy to transform carbon dioxide gas (a.k.a. CO2) into organic carbon (the di-oxide part from carbon dioxide is released as di-oxygen gas – what we breathe in, what flows through our blood, our bodies).

But there’s a catch. Unlike carbon dioxide gas and light, the organic carbon that makes up phytoplankton biomass feels the tug of gravity. It starts to sink. Phytoplankton may sink slowly at first, but their descent quickens as they are grazed, digested, compacted, and (ahem) expelled back out. In this new state, biomass sinks out of the sunlit ocean and down into the abyss.

Still, the ocean is very deep and it might take several months for biomass to sink from the ocean’s surface to the seafloor. Many such particles will never get there. Like leftovers spoiling in a refrigerator, someone’s trash is another’s treasure. The deep ocean is the world’s largest food desert, and so when something digestible passes by – no matter how gross – its thanksgiving to the microbes living there. Like us, these microbes eat organic carbon, breathe in oxygen, and burp out carbon dioxide (which dissolves in deep ocean seawater).

So the ocean’s heart – its carbon pump – moves carbon dioxide from the surface ocean into the deep sea. This deficit of carbon dioxide gas at the sea surface allows CO2 from the atmosphere to dissolve into surface waters, where it too can get pumped down into the abyss.

We’re all hoping that the ocean’s carbon pump is resilient to global warming and climate change – in fact we’re relying on it to take much of the atmospheric CO2 that we humans have released and sequester it in the deep sea. But there’s still reason to be vigilant. There’s evidence from the past that the carbon pump can change, and that these changes have global consequences. In fact, an unusually strong carbon pump tens of thousands of years ago led to an ice age, storing more carbon dioxide in the deep ocean, with less in the atmosphere. The opposite of modern climate change where high CO2 leads to global warming, lower amounts of CO2 in the atmosphere of the past cooled the planet, helping to build massive glaciers worldwide.

Although a number of phytoplankton species can grow at freezing temperatures, if the ocean gets too warm, many won’t survive. A major worry about modern global warming is that overheated phytoplankton might make the carbon pump less efficient, and that this will slow CO2 removal from the atmosphere. Warmer oceans might also inspire bacteria to degrade organic matter more quickly – similar to food left out in the open will go bad fast compared to food in the fridge – and so fewer particles may sink to the deep ocean.

What we’re doing out here, in essence, is a check-up. Scientists have been coming to this location – Station ALOHA – for the last 40 years, tracking how many phytoplankton are growing in the surface, and how much is sinking to the deep. We’re here to pitch in: continuing this vital record of ocean health will allow changes in the biological pump to be diagnosed early on. The moving parts of the ocean’s carbon pump may be too small to see, but its too important to ignore.


When you’re working at sea, safety is key – Erin Black

Andddd go! The first mate throws a flagged buoy off the back of the ship. It hits the water with a crash and begins to bob in the waves. “Man overboard!” someone shouts. Right away, two scientists point, full-armed, at the buoy. It’s their job to be the spotters. No matter where the buoy goes, they point. The captain is notified to slow the research vessel so that a rescue boat can be launched to pick up the ‘man overboard’. By the time the rescue boat makes it to the buoy, it’s been 10 minutes and the buoy is barely visible as the waves move up and down between the vessel and the buoy. The buoy is recovered and the new ship-goers have learned a valuable lesson. This is the best-case scenario that could happen if, perhaps, you reached too far out to grab some research equipment or walked too close to an unsecured opening and toppled overboard. The sun is shining. Two spotters are watching you. The entire crew is mobilized to come pick you up while you tread water. The take homes from this drill: safety first, always have one hand for the ship, and tell someone where you are. If you take risks, fall off the back deck at nighttime, and you didn’t tell your bunk mate that you were quickly checking on some scientific samples…you may be in the water a very long time or worse.

Thinking about safety is a large part of your everyday job when you do science at sea. There are the obvious dangers, such as the winch wire, ship cranes, and large oceanographic equipment. You stay away from these unless you’re properly trained and wearing a hardhat. However, something as simple as stairs can become a hazard at sea if the boat rocks at the right time. Try to imagine doing everything that you do in a day while swaying side to side. Sleeping (back and forth), eating (back and forth), and showering (back and forth). Moreover, ocean scientists must perform their research while the boat is inconsistently shifting this way and that. Imagine pouring a mixture from one beaker to the next under these conditions. Imagine that mixture is a dangerous acid. As scientists, we take steps to minimize ‘typical’ science actions like pouring, because one sharp roll of the ship can mean a spill. We secure everything we use with ties and straps. A ‘secured’ lab might look a bit silly with bungee cords on this and ratchet straps on that. It’s certainly annoying to remove the ties each time you need to do something. However, at sea, safety is serious business and is the key to successful research.

Tools we use at sea: sediment traps and in situ pumps for sinking vs. suspended particles

A tremendous quantity of animals, particles (dead and alive), and chemicals occupy the open ocean. Even in the nutrient-deplete, oligotrophic waters of the North Pacific Subtropical Gyre.

Animals and filamentous cyanobacteria
A small zooplankton net was the first package we deployed upon arrival to station ALOHA at 00:00 this morning. Angel White’s dreamy photo shows many different (relatively larger) ocean occupants gathered in this tow, including the seasonally abundant nitrogen-fixing filamentous cyanobacteria Trichodesmium.

Particles: sinking and suspended
For geochemists there are 2 types of particles, sinking (dead) and suspended (alive). These particles are usually the main food source for zooplankton. Suspended particles consist of phytoplankton cells, heterotrophic protists, and bacteria that are actively growing. While sinking particles tend to be larger, heavier aggregates of partly consumed plankton, fecal pellets, and amorphous organic matter. To capture these different types of particles we use different sampling devices: sediment traps are used to collect the sinking material and the CTD rosette or in situ pumps are used to collect the suspended material.
Under a full moon, our first free-floating sediment trap array was deployed at 02:50 by BB. Cael, Erin Black, Bethanie Edwards, and Tara Clemente.

12 trap tubes filled with brine and fixative were supported by cross-arms mounted at three depths (300, 150, 75m). At the surface of the array a beacon was attached so we can retrieve the trap. Using the ship’s ADCP (http://currents.soest.hawaii.edu/hot/) to observe water column currents, Matt Church and Tara Clemente decided to deploy the sediment traps just north (22°51.9810N 158°03.7939W) of ALOHA’s 6 mile radius circle (http://aco-ssds.soest.hawaii.edu/ALOHA/). Over the next 3 days the sediment trap array will drift through (and likely beyond) station ALOHA.
To collect suspended particles, many cruise participants are content using water from the CTD rosette Niskin bottles. The rosette holds 24 bottles with 12L capacity, so many different depths can be sampled. Or if you want, just 1-2 depths, but then you have a lot of water to put into carboys and carry around to the lab to filter. Here is a photo I took of Katherine Heal in the Hydro lab helping Wei Qin filter water from 1000m and 770m, only a few of the carboys are shown.

Other participants need more than 288L in order to measure trace metals, compound-specific isotopes, enzymes, and DNA. For this we use McLane pumps that can be deployed to a specific depth, and using battery power pump 1,920L filter over a 4-hour deployment. For these deployments we add a pre-filter to keep the sinking material separate from the in situ, actively growing organisms. Our first McLane pump deployment will be tonight, right after dinner.