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Subscribe to this list via RSS Blog posts tagged in deep sea


My name is Natalie Slayden. I am a Master’s student at Nova Southeastern University working in Dr. Tracey Sutton’s Oceanic Ecology Lab. I am studying the age and growth of deep-pelagic fishes, with case studies of meso- and bathypelagic species from the Gulf of Mexico.

All fishes have three pairs of otoliths. Otoliths are often referred to as ear stones and are located in the cranial cavity of fishes. Otoliths come in different shapes and sizes depending on the species. Therefore, otoliths can be used to identify fish species. Fishes have otoliths to help them detect sound & orient themselves in the water column. Otoliths can tell us a lot about a fish’s life history and they can also be used to determine age.


Left: Both sides of an otolith from the species Ceratoscopelus warmingii (Rivaton & Philippe, 1999).  Right: Awesome picture of a Ceratoscopelus warmingii taken by Danté Fenolio.   

Have you ever heard of tree rings? Trees have rings that can be counted to reveal how old they are. Otoliths have rings too! These rings can be formed daily, monthly, yearly, or during events such as feeding. Like tree rings, otolith rings can be counted to determine age. Most previous research has focused on aging coastal fishes. Now, I am working to age some mesopelagic (200 – 1000 m) and bathypelagic (deeper than 1000 m) fishes. 


Above: The otolith rings of three different species (Gartner, 1991)

Fisheries have become interested in deep-sea fishes to utilize them as feed for aquaculture and as oil for omega dietary supplements. Since they are a target for fisheries, it is important that we understand how long these deep-sea fishes live. Some deep-sea fishes have rings that are formed daily. Most of these fishes with daily rings perform a daily diel vertical migration, meaning they swim from the depths up towards the surface waters at night to feed and then swim back down to the depths at dawn to avoid visual predators. Lanternfishes are one group of fishes that undergo this migration pattern and usually have an age of one year or less. We think that the daily rings are formed due to light or temperature changes that occur during their daily vertical migration. However, for fishes that do not vertically migrate and remain at depth, it is uncertain what their otolith rings represent. Are they daily or yearly? Could they represent a single meal? 

So, for my thesis project I will attempt to determine what an otolith ring represents for a non-vertically migrating deep-sea fish. Second, I will be describing the otolith ring patterns and correlating those patterns to the life history of my case study fishes. Lastly, I will be providing age estimations for a number of mesopelagic and bathypelagic fishes. 


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Hello, everyone! My name is Kristian Ramkissoon, and I am a graduate student working in the Oceanic Ecology Lab with Dr. Tracey Sutton. As a member of the lab, I am currently studying the species composition, abundance, and vertical distribution of the deep-sea fish genus Cyclothone, whose combined numbers make it the most abundant vertebrate on the planet. This study of Cyclothone in the Gulf of Mexico is one of the first of its kind. So what are Cyclothone? The name Cyclothone refers to a specific genus of fish which includes a number of different species. They are more commonly known as bristlemouths. Below are some of the more common species that we have collected in the Gulf of Mexico.


From left to right:(Top Row) Cyclothone pseudopallida, Cyclothone braueri,
(Bottom Row) Cyclothone obscura, Cyclothone pallida


Bristlemouths are close relatives of another abundant group of deep-sea fishes, the dragonfishes, and can similarly be found within the meso- and bathypelagic zones of the ocean. Unlike their more infamous cousins, however, Cyclothone are much smaller in size and much less active (many of the Cyclothone we encounter on our cruises are hardly an inch long!)


Cyclothone pallida against a ruler and under the microscope.

Collectively, these fishes have a near-ubiquitous distribution, with various species found throughout the world’s oceans. This worldwide presence, along with their status as the most abundant known vertebrate, make understanding Cyclothone important for understanding the ecology of the deep sea. As a part of my research into the world of bristlemouths, I spent a lot of time learning the unique features that distinguish each species from one another. Some of the common traits that I used to distinguish between different Cyclothone species were skin color, tooth shape, and gill morphology. To date we have identified thousands of individual Cyclothone down to the species level, keeping close counts and measures of each!


Pigmentation found on the head of (A) Cyclothone alba, (B-C) Cyclothone atraria, (D-F) Cyclothone braueri, and (G-J) Cyclothone pseudopallida.

Body, pigmentation, and photophores of Cyclothone pseudopallida.


So far, my research has revealed quite a few interesting things about these tiny denizens of the deep! For one, we have confirmed that Cyclothone in the Gulf of Mexico, similarly to those elsewhere in the world, do not vertically migrate. Additionally, the taxonomic data collected, in combination with data from the MOCNESS (Multiple Opening Closing Net and Environmental Sensing System) seem to suggest that all six species commonly found within the first 1500 meters of the northern Gulf of Mexico occupy relatively tight and distinct depth ranges. This information tells us that Cyclothone, unlike many other deep-living predators who migrate daily, may subsist entirely on what is found at their respective depth ranges (in the deep, this can be very little!). In addition, we are attempting to assess the impact that hydrographic features such as the Loop Current and eddies formed by it may have on the distribution of Cyclothone within the Gulf of Mexico.

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My name is Matt Woodstock. I am a master’s student at Nova Southeastern University studying under Dr. Tracey Sutton. My thesis project is about the trophic ecology and parasitism of mesopelagic (open ocean, 200 – 1000 m depth) fishes in the Gulf of Mexico. 

Mesopelagic fishes are important consumers of small crustaceans (shrimp-like animals) and are prey of oceanic predators (e.g. tunas and billfishes). Some mesopelagic fishes undertake a diel vertical migration, meaning these fishes migrate up into the near-surface waters at night and then migrate back down into the deep, dark depths during the day. These fishes migrate so that they can avoid visual predators in the epipelagic (0-200 m) during the day but take full advantage of the abundant food supply there at night under the cover of darkness. Other mesopelagic fishes do not vertically migrate and remain deep at night. A lot of animals participate in this daily movement and it is regarded as the largest daily animal migration on Earth! 

b2ap3_thumbnail_MW-pic-1.jpg      b2ap3_thumbnail_MW-pic-2.jpg

A hatchetfish (left) and a lanternfish (right). The hatchetfish does not undergo a daily vertical migration, but the lanternfish does. Images courtesy of DEEPEND/Dante Fenolio.


So what exactly do I study? My job is to dissect a wide variety of fishes and identify their gut contents and parasites. The gut contents obviously tell us what the fish has recently eaten, but the parasites I am interested in are transmitted through their diet. Certain parasites, called endoparasites, live within another animal (a host) and must go through different animals to complete their life cycle. If I find a lot of the same parasite in the same species of fish that means that fish has eaten the same prey item for the majority of its life. If I find a lot of different parasites within a species, then the diet of that fish may have shifted at some point in its life, or that fish may have a general diet where it eats many different types of prey. Results from this type of study allow us to make conclusions about the connectivity and stability of different ecosystems.

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Two roundworms from fishes on DEEPEND cruises. On the left picture, notice the white, swirly looking object. This parasite is attached to the intestine, where it feeds on the digested nutrients of the host’s food. 


The coolest part about my project is that many of the fishes I study have never been examined for parasites before. That means that I am the first person to see a parasite within that fish before (or I am at least the first person to write it down)! I am also studying the external parasites, called ectoparasites, of these fishes as I find them. These parasites are unique because they spend part of their lives searching for a host to latch onto, and then they attach themselves to a host for the remainder of their life (normally)! They also make for a great picture!


Two types of external parasites from fishes captured during DEEPEND cruises. These parasites will attach themselves to the host through the scales and feed on the host’s tissue or previously digested food.

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My name is Rich Jones and I am a master’s student in Dr. Jon A. Moore’s lab at the Florida Atlantic University’s Honors College. Dr. Moore is an ichthyologist who has been working closely with DEEPEND since the beginning helping to identify some of the obscure and poorly studied deep-sea fishes collected from these depths. For myself, as someone who has always been excited about biodiversity, this work has been one of the greatest privileges of my life. Some of the fishes we have identified have only been seen by a handful of people before in the history of the world. The opportunity to study the habits of these rare animals with a comprehensive suite of data, let alone hold them in your hand, is a unique pleasure of working with DEEPEND. Some of the fishes we caught were less rare, but equally as mysterious in how poorly studied they are. One such obscure group entrusted to our lab were the Paralepididae, commonly known as “barracudina” due to their superficial resemblance to small barracuda (they are not related to barracuda). Samples collected by DEEPEND and NOAA cruises have presented a rare and unique opportunity to study these enigmatic little fishes, and I have spent the past few years getting to know them through my thesis research investigating their basic life history in the deep Gulf of Mexico.

Pictured here is a duck-billed barracudina (Magnisudis sp.) in its natural habitat, deep in the ocean. Duck-billed barracudina are some of the largest of the barracudinas and can grow to lengths of about one meter (3 feet). They are members of the sub-group known as “scaly” barracudina because they have more scales than the other varieties. This photograph is an extremely uncommon example of a live barracudina, taken by the NOAA Okeanos Explorer’s Remotely Operated Vehicle (or ROV) as it descended through the mid-water to survey the deep seafloor of the Gulf of Mexico.

At first, I knew nothing about barracudina. I wanted to focus on them for my master’s thesis research simply because they were so poorly studied. Once I began to get to know them, I learned that there are a lot of amazing and strange things that make these little fish special. Many of the smallest species are almost completely transparent in life, lacking all but a few scales. Some of those transparent species possess a unique type of bioluminescence along their bellies which is derived from their liver tissues. They use this bioluminescence to counter-shade their silhouettes against the dim light down-welling into the deep sea. They are all simultaneous hermaphrodites which means that they are both males and females at the same time throughout their entire lives. This type of reproductive mode is extremely rare among vertebrates but likely a useful quality in the deep-sea where encounters with potential mates are rare. They are very closely related to lancetfish (Alepisauridae) which are some of the biggest and baddest fish found in the deep pelagic. They can grow to lengths greater than 2.5 meters (8 feet)! Unlike barracudina, lancetfish are well studied because they are frequently caught as bycatch in pelagic long-line fisheries. So much so that they are often considered a pest to that fishery! The lancetfish’s smaller relatives, the barracudina, are not directly caught by the long-line fishers themselves but are frequently documented in the stomachs of those fishers’ targets, swordfish and big-eye tuna. In fact, several barracudina species were first described by science based on specimens found in the stomachs of fish bought at fish markets.

Pictured here is a juvenile javelin barracudina (Lestrolepis intermedia) collected during a DEEPEND cruise. This species is one of the “naked” barracudina, so called because they lack most scales and are highly translucent. This species has a unique bioluminescent organ that runs along its belly in a straight line and an additional photophore spot just in front of each eye. In life, these fish glow a faint yellow color. Observations from submersible expeditions in the 1950’s reported that this species exhibits a unique swimming behavior in which it orients itself vertically in the water column, rapidly switching its orientation from upwards to downwards.

Part of the reason barracudina are so poorly studied is because they are only infrequently captured in net trawls, and the specimens that are caught by nets are usually smaller representatives for their species. Given that they are infrequent and small in net sampling but frequent and large in the guts of certain top-predator fishes could mean that they are more common than we know and that they are just fast enough swimmers to avoid the nets. It could also be that barracudina are generally uncommon and just one of many important prey types to those deep-diving delicacies of the fish market. Either way, barracudina are under-appreciated, and as our impacts on the ocean increase, whether from industrial fishing, climate change, or oil spills, we will need to know more about the favorite prey of our favorite seafood to inform us about the sustainability of those treasured pelagic resources.

To that end, my work with barracudina has two main goals: (A) identify ecological patterns among the barracudina species in the Gulf of Mexico and (B) develop an easy to use key for identifying these often difficult-to-distinguish species. Regarding their ecology, I am asking some very basic questions: (1) What depths do the different species inhabit? (2) Do they vertically migrate? (3) How easily can they avoid the nets? (4) What do adult barracudina eat? And (5) Where in the water column are adults and juveniles found, respectively?

A picture of a typical sample from a MOCNESS tow that includes the common naked barracudina (Lestidiops affinis; center of photo) among other mesopelagic fishes like lanternfish and bristlemouths. While barracudina are not the most abundant, small swimmers of the deep sea, they are still relevant as they are a favorite food item for deep-diving tunas, billfishes, whales, and sharks.

What I have found is partly to be expected and partly surprising.  It is not surprising, for example, that net avoidance is common among barracudina. The NOAA cruises immediately after the Deepwater Horizon oil spill utilized two different net types to sample the deep Gulf. One was a high-speed rope trawl and the other a multiple opening and closing net and environmental sensing system (or MOCNESS), which the DEEPEND cruises also employed. The mouth area of the MOCNESS is fairly small and because the net mesh size is only 3mm in diameter it cannot be towed very fast. This increases the potential for net avoidance by larger, faster swimmers. The rope trawl, on the other hand, had a much larger mouth area and could be towed much faster which made it more difficult to avoid. The rope trawl caught significantly more and significantly larger barracudina than the MOCNESS, which was to be expected.

Another unsurprising, but important, finding was that different barracudina species occupy distinctly different layers of the water column. It seems that there is a general distinction between where in the depths you find the “scaly” and “naked” barracudina types. The smaller, translucent or “naked” types are significantly more common near the surface in the lower epipelagic while the larger “scaly” types are almost exclusively found in the twilight zone of the mesopelagic. However, while the naked barracudina are much more common near the surface, they can be found throughout the water column all the way to the deepest, darkest depths. Comparing abundances caught at depth between day and night, there does appear to be a slight, but far from significant, amount of vertical migration in barracudina. I suspect that the reason there appears to be any vertical migration at all in these species may be that they are chasing their food, most of which does vertically migrate to the surface waters at night to feed.

Dietary habits also had a similar distinction between the two main types of barracudina. After dissecting the stomachs of several hundred adult specimens, I found that the naked ones seemed to be exclusively eating migrating mesopelagic fishes while the scaly types were eating mostly deep-sea shrimps. This is somewhat surprising because we would expect that small fishes, like barracudina, living in the deep sea would eat whatever they encounter and would not be very picky. It is likely that these differences in dietary habits and apparent selectivity are the result of a combination of their preferred habitats and their unique feeding behaviors, which continue to remain unclear. Rare observations from the voyages of the French submersible Bathyscaphe Trieste in the 1950’s reported that one barracudina species (Lestrolepis intermedia) indeed swims quite rapidly through the water column, “like silvery javelins”, occasionally halting to “float along like erect pieces of asparagus”, rapidly changing their orientation from looking upwards to looking downwards. It is unknown whether this is a unique hunting behavior or predator avoidance behavior or both. It is also unclear whether all barracudina species exhibit this odd behavior.

The apparent differences in distribution and diet I have found among the barracudina in the Gulf of Mexico could prove to be useful information as the different species appear to reflect distinct aspects of the deep-pelagic ecosystem where they live. The presence or absence of certain barracudina from a given area or large fish’s stomach could be used to help make inferences about the state of the greater pelagic environment. In managing an entire ecosystem, fishery managers rely on suites of different indicator species to inform them about the ecosystems that sustain our living ocean resources. For these suites of indicators to be effective, however, managers need to able to correctly identify them to their respective species. Many barracudina, especially the naked ones, are very difficult to identify to species and the keys that exist to diagnose them often require counting the number of vertebrae they have which is not an easy thing for most managers to do. As such, another goal of my research is to provide an easy-to-use dichotomous key that relies on simple measurements and illustrations of pigments to aid quick but accurate identification to species. Helping me to complete this goal is Ray Simpson, a post-doctoral researcher based at the Yale Peabody Museum, who is an excellent illustrator.

An illustration of the Spotback Barracudina (Uncisudis advena) by Ray Simpson

A picture of one of the largest (>15cm) ever recorded specimens of the Gulf of Mexico Bullis’s Barracudina (Stemonsudis bullisi). This endemic species had previously only been known and described from two juvenile specimens around 6cm long.

Like the DEEPEND consortium itself, the over-arching goal of my research is to contribute to a baseline of data that will inform future research and monitoring efforts in the deep Gulf of Mexico. In this way, even our simplest findings are superlative: three of the nineteen barracudina species captured in our samples represent first records for those species in the Gulf of Mexico, and the overall ranges of several other species have been expanded significantly thanks to our sampling efforts. We captured the largest specimens ever recorded for one species which is only known from the Gulf of Mexico. Hopefully publishing these results in an open-access outlet will provide useful information to managers when the next spill happens or when changes in deep-sea fisheries management need specific monitoring criteria. Regardless, it has been a real pleasure working with these odd little swimmers from the shadowy depths.

Check out Ray Simpson’s website here:
It is an online outlet for Ray’s illustrations and an exhaustive list of Fishes of the Western North Atlantic which reads like a field guide.

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Hello everyone,

My name is Ronald Sieber. I am a Master’s student at Nova Southeastern University working under Dr. Tamara Frank in the Deep Sea Biology Lab. I work with Dr. Frank as a graduate research assistant studying deep sea shrimp in the northern Gulf of Mexico. My work pertains to the general distribution and abundance of the deep sea shrimp family Benthesicymidae.

The family Benthesicymidae consists of 39 species across five genera, the most speciose of which are Gennadas (16 species) and Benthesicymus (15 species). Thus far we have collected two genera (Gennadas and Bentheogennema) consisting of six species. While the family in general can be identified by a blade-like rostrum and a bearded appearance due to the presence of setae tufts, the individual species can only be identified by the shape and structure of the genitalia. The structures are known as petasma (for males) and thylecum (for females).

Image of Bentheogennema intermedia displaying the truncate and blade-like rostrum typical of all members of the family Benthesicymidae. Adapted from Orrell and Hollowell, 2017.



Petasma (a) and thylecum (b) for Gennadas bouvieri adapted from (Kensley 1971) and Bentheogennema intermedia from (Perez Farfante and Kensley 1997). Petasmas are composed of three variously shaped lobes while thyleca are composed of various processes and flaps on the 6th, 7th, and 8th sternites that are species specific and easily identifiable.

This study is trying to establish a broader understanding of the Benthesicymidae assemblage in this region of the Gulf of Mexico. It will also look into potential abundance shifts for the individual species to see if there have been any increases or decreases in quantity over the seven years that samples have been collected. Also, this study is looking into the potential impact that the Loop Current poses to the vertical migration of the Benthesicymidae. This current, which is sporadically present in the region of study, causes an abrupt shift in water temperature that is unfavorable for these shrimp. While initial results show an impact in abundance due to Loop Current presence, further statistical analyses are required to show the potential migration shifts that the current poses.


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Hello! My name is Ryan Bos and I am a Masters Candidate in Marine Science at Nova Southeastern University.  Currently, I am doing an appraisal of microplastic ingestion in deep-pelagic fishes and crustaceans in the Gulf of Mexico (GoM) with Dr. Tamara Frank and Dr. Tracey Sutton.

Each day, nearly every person on Earth uses plastic items. It is all around us. It is in our clothes, cosmetics, vehicles, and if you carry a smartphone around with you, odds are that it has a plastic component. As humans, we manufacture and use plastic at alarming rates, and take it for granted. Plastic production is projected to increase with increases in the human population, yet plastic pollution is already infesting our oceans and will continue to persist for hundreds to thousands of years because of plastic’s inherent resiliency. I want to put the plastic crisis we are facing into perspective.  There are ~34,000 extant species of fishes, with the most abundant genus of fish, Cyclothone, consisting of 13 species. These 13 species comprise an estimated 1,000,000,000,000,000 individuals. By the year 2050, the number of fishes in our oceans will be equal to the number of plastics. What is alarming about this statistic other than the number of fishes and plastic particles being equal? There are 33,987 more species that contribute to the total number of individual fishes in our oceans, and most of these plastic particles cannot be seen with the naked eye! 

Deep-sea micronekton are integral parts of pelagic ecosystems, as they serve as key intermediates in oceanic food webs, contribute significantly to overall abundance and biomass, make substantial contributions to carbon flux, and serve as links between shallow and deep-pelagic waters. Thus, they are exemplary targets for microplastic studies.

Microplastics, as the name implies are small pieces of plastic that range in size from 1 µm - 5 mm that are categorized as being a fragment, film, spherule, foam, or fiber.  Once ingested, an animal may experience pseudosatiation (the feeling that they are full but have not received any nutrition), obstruction of feeding appendages, decreased reproductive fitness, and death. Pictures of these categories are portrayed below, excluding foams, of which none were found.  To determine if a particle is a piece of plastic, we used the ‘hot-needle,’ or ‘burn-test.’ It is a rapid and cost-effective technique for plastic determination. When plastic is probed with a hot-needle it either leaves a burn mark, melts, or in the case of fibers, curls up and is repelled by the needle.  


Regrettably, there are no previous estimates of microplastic ingestion by deep-sea fishes and crustaceans in the GoM, despite the commercial importance of this ecosystem.  A total of 723 individuals (316 fishes and 407 crustaceans) from a combined 48 species and 11 families were dissected and visually inspected for microplastics.  Plastic items were found in both fishes and crustaceans. A total of 263 microplastics were identified, with crustaceans and fishes consuming 146 and 117 microplastics, respectively.  Total micronektonic crustacean and fish plastic ingestion was approximately 31 % (n = 190/618) while 16 % of euphausiids (n = 96) and 11 % of crabs (n = 9) contained at least one piece of plastic.

Interestingly, there were apparent differences in type and number of microplastics ingested by fishes and crustaceans, with crustaceans ingesting predominantly fibers, as opposed to fishes, which consumed a substantial number of fragments. Further, vertically migrating taxa of fishes contained more microplastics than non-migratory taxa, but the opposite trend was observed in crustaceans. In fact, non-migratory crustaceans consumed significantly more plastic than all other taxa. Curiously, the non-migratory crustacean taxon with the highest frequency of plastic ingestion, the Benthesicymidae, are all habitual consumers of marine snow. That, coupled with the smaller size classes of microplastics found in this study, may be indicative of marine snow’s importance in biogeochemical cycling of microplastics.  

As commercial fishing efforts scale up to harvest the deeper layers of the ocean, these results will be important for assessing risk associated with consumption or indirect consumption by the deep-sea biota. Importantly, larger deep-pelagic crustaceans appeared to have more plastic in them than small conspecifics, but size was not indicative of plastic ingestion by fishes, and no significance was observed for either group of animals.


 Empirical cumulative distribution functions of carapace length of crustaceans (A) and standard length of fishes (B) that did and did not ingest microplastics. Two separate (one for crustaceans, one for fishes) Kolmogorov-Smirnov tests generated p-values of 0.09 and 0.924, respectively.


Deep-sea food webs are largely understudied relative to coastal studies, but results to date suggest a great deal of complexity.  Our data reveal that more scrutiny should be given to deep-sea ecosystems with regards to plastic ingestion. These food webs are understudied because of the enormous expense and difficulty of obtaining deep-sea samples, highlighting the importance of projects such as DEEPEND.

If you are interested in learning more about our work or how to aid in the fight against plastic, please get in touch with me by email: This email address is being protected from spambots. You need JavaScript enabled to view it.

A brilliant new way to aid in the fight against plastic by doing laundry:

A resource for learning more about plastic:

An article about how plastic is killing our oceans, by Wendy Lipscomb from the website 'It's a fish thing':


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