Weedlines: A Sargassum Research Blog

Meet the Scientists

We’re off in search of Sargassum! We have a mixture of Sargassum veterans and a few new faces for this leg. Check out who’s going and learn a little bit about our science team, and thanks for following along on our blog.

Frank HernandezDr. Frank Hernandez (Chief Scientist, Lead Investigator, USM)

Dr. Hernandez is an Assistant Professor in the Department of Coastal Sciences at the University of Southern Mississippi where his research focus is in fisheries oceanography. His research interests include larval and juvenile fish ecology, biophysical processes that influence recruitment dynamics, fish-habitat associations, planktonic food webs, and the impacts of environment/climate variability and anthropogenic disturbances on the ecology of fish early life stages. He spends way too much time at his desk or in meetings, and is therefore thrilled to be going offshore again in search of Sargassum.

Kevin DillonDr. Kevin Dillon (Co-Investigator, USM)

Dr. Kevin Dillon is a chemical oceanographer and associate professor in USM’s Division of Coastal Science. His research interests include carbon/nutrient cycling and food webs in aquatic environments and the impact of anthropogenic stressors to these ecosystems. In this study he is using bulk stable isotopes (13C and 15N) as well as compound specific stable isotopes of amino acids to elucidate food web dynamics in Sargassum communities.  He is grateful for this brief escape from the lab for some well-deserved time at sea with his PhD students exploring the mysteries of Sargassum.

Carla CulpepperCarla Culpepper (Research Technician, USM)

Carla is a technician and lab manager of the Fisheries Oceanography and Ecology Lab in the Department of Coastal Sciences at the University of Southern Mississippi. Her research interests are in plankton dynamics in the northern Gulf of Mexico, particularly, the interactions between zooplankton and ichthyoplankton. By the end of this cruise, she will have spent roughly sixty days aboard the R/V Point Sur; it has become a home away from home.

Eric Haffey (Research Technician, USM)

Eric HaffeyEric is a technician that joined the lab January of 2017 identifying larvae fish as part of the CONCORDE project. Prior to being a part of our lab he worked at the Baruch Field Laboratory USC in South Carolina working with planktonic samples and early life stage tarpon. He looks to expand his knowledge of early life stage fishes and is excited to partake on his first research cruise on the R/V Point Sur.

Valeria NunezValeria Nuñez (Research Technician, USM)

Valeria started in early February as research technician in the lab. She came to Mississippi from Texas after graduating from Texas A&M University-Corpus Christi in December. Though she is taking a break from school, she continues to expand her knowledge and skill in research so going back out to sea is an exciting opportunity for her to do just that.


Olivia LestradeOlivia Lestrade (Graduate Student, USM)

Olivia is a Master’s student in the Fisheries, Oceanography, and Ecology lab at the University of Southern Mississippi. Her research focuses on microplastic impacts to early life stage fishes associated with floating Sargassum habitats. She has been a fish out of water her whole life and has a passion for understanding and exploring the Gulf of Mexico.


Courtney StachowiakCourtney Stachowiak (Graduate Student, USM)

Courtney is working to obtain her MS in Coastal Sciences at the University of Southern Mississippi’s Gulf Coast Research Lab. Her research is funded by the NOAA RESTORE program and is focused on assessing the juvenile fish community assemblages associated with Sargassum, and targeting important fishery species to quantify age and growth parameters. She hopes to pursue a career in fisheries research as she enjoys field sampling, and she is looking forward to her second research cruise aboard the R/V Point Sur.

Zabe PromoElizabeth (Zabe) Premo (Graduate Student, USM)

Zabe is a PhD student in the Department of Coastal Studies at the University of Southern Mississippi working under the advisement of Dr. Kevin Dillon, and is undertaking research focused on stable isotope ecology and marine nutrient cycling. She is funded by NOAA RESTORE, and her main efforts as part of this project focus on bulk and compound specific stable isotope analysis of biological samples to investigate trophic structure associated with Sargassum features. Zabe is extremely grateful for the opportunity to go to sea, and intends to unabashedly geek out with each new Sargassum sighting.

Caitlin SlifeCaitlin Slife (Graduate Student, USM)

Caitlin is a PhD graduate research assistant in Dr. Dillon’s chemical oceanography and biogeochemistry laboratory at the University of Southern Mississippi. She is a stable isotope ecologist whose research is focused on modeling trophic webs via bulk isotope and nutrient analysis. She typically only goes offshore for a few days, so she is very excited to spend an extended period offshore working on Sargassum


DSC_3685b ©Brian Jones 2017Angie Hoover (Graduate Student, USM)

Angie is a Coastal Sciences Master’s student at USM, studying larval fish diet, growth and condition in relation to anthropogenically-induced environmental factors such as freshwater discharge and hypoxia. Being in the field is Angie’s favorite part of her job, so she is very excited to tag along on this cruise and help her fellow graduate students sample for their projects.

Alex SandercockAlex Sandercock (Undergraduate Intern, USM)

Alex is currently a Biology major at The University of Southern Mississippi. Following graduation, he is hoping to further his studies with a graduate degree in Biology. This will be Alex’s first summer participating with the Sargassum cruise and he is looking forward to the experiences that he will have.


Anna Millender.pngAnna Millender (Undergradute Intern, USM)

Anna is an undergraduate majoring in Marine Biology at USM in Long Beach. Her interests are broad; she usually finds something fascinating about anything ocean related but she’s most interested in the megafauna associated with Sargassum on this cruise. She considers herself a thalassophile and feels most at home when at sea, so she’s excited to be spending time out in the deep blue.

April Hugi April Hugi (Soon to be graduate student, USM)

April is a new intern in the Hernandez lab and will be starting graduate school in the fall. She is interested in larval fish ecology, fish-habitat associations, and ecosystem-based fisheries management. Her eventual goal is to pursue a career where she can link her two passions of marine science and visual art to help bridge the communication gap between the public and the scientific community. She is excited to embark on her first research cruise and hopes the experience will inspire her scientific and artistic creations. 

 Nudibranch (with Beatrice)

Nudibranch (Sea Turtle, Guest Lovie)

Nudibranch is going on her second research cruise, courtesy of Frank’s daughter, Beatrice. Nudibranch will help in several important ways. First, she will use her sea turtle powers to help the team locate Sargassum at sea. Second, she will help scan the weedlines and ensure that our sampling region is “turtle free”, and that we are okay to deploy our nets. Lastly, she will keep Beatrice’s dad company, so that he will not be lonely and miss his family so much.

Weedlines: A Sargassum Research Blog

PS-18-05 Daily Log

June 6, 2018 (Day 8)*

*Note: these will be posted on a one-day delay, i.e., this report is for yesterday’s activities.

We’ve had great luck with the weather so far (remember Alberto?), but all good things come to an end. Our last day of sampling was shortened due to storms in the area and rough seas. Here is a short synopsis of some of the day’s activities.


If able, we will grab debris from the water. In this particular rig, we found some polychaetes hiding!

Our decision to hold position overnight was a good one; we woke up to large patches and mats of Sargassum, flowing up the the Loop Current and into the Gulf of Mexico. That was the good news. The bad news is that the winds had picked up overnight and the seas were choppy, with whitecaps and swells. We started our sampling ops with a neuston tow along a weedline, which was moderately successful. The net ‘gulped’ in and out of the water with the waves and winds, so it was not the prettiest tow we’ve done. But, we managed to sample some Sargassum and a few associated fishes and invertebrates. Like our previous net tows in this region, relatively few organisms overall. After a successful CTD cast and water collection, we then attempted a Sabiki fishing set. However, it was difficult to maintain a position near Sargassum for an extended period of time, so we abandoned this fishing effort after several attempts.



Storms on the horizon (Photo: Brian Jones)

The seas continued to worsen and there were numerous storms in the vicinity, therefore we could not conduct small boat ops or collect Sargassum reflectance data. Since we were 25-26 hours from port, we set a heading for home in the hopes of encountering calmer seas, brighter skies and better overall sampling conditions.  The next several hours were spent plowing north through rough seas. Eventually conditions improved, however the sun was setting quickly. We made an attempt to collect additional reflectance data before sunset, but ultimately this was not successful. Having done our best, we resumed our course for Gulfport where we expect to arrive tomorrow afternoon.

Mengqiu and Xingxing.jpg

Dr. Xingxing Han and Mengqiu Wang relax on during our last beautiful sunset. (Photo: Brian Jones)

Overall, this has been a successful cruise, albeit very different than last year’s effort. We were able to collect Sargassum data in two very different environmental regimes, which will be very valuable in our assessment Sargassum and its value to fish early life history stages.

I want to thank the captain and crew of the R/V Point Sur for another great cruise; they made everything possible and we really appreciate what they do for us. Special thanks to our science team for putting in the long hours to get the job done. Also thanks to the NOAA RESTORE program for supporting this research.


The Hernandez crew relaxing after a long day with some card games.

And lastly, thanks to everyone who followed along with us on the cruise blog! This was our first attempt at sharing our science while at sea. We hope it was informative and entertaining. We have another cruise in July, so stay tuned for more Weedlines.



Weedlines: A Sargassum Research Blog

Microplastics and Sargassum


Much of the debris we find are in the form of single use items like this floss pick.

Marine debris is defined as any persistent solid object that is manufactured and disposed of into the marine environment (intentionally or unintentionally). The most dominate form of marine debris is plastic (60- 80%). Plastics are easily moldable, inexpensive to produce, and durable. Their production has continually increased since the 1950s because of their popularity in the consumer world. They have a long life because of their resistance to degradation and much of it ends up in landfills, and in many cases, the ocean. As plastics float in the ocean, they gradually break down because of solar radiation, physical processes, and biodegradation. From this, smaller pieces of plastic form known as microplastics, which are pieces smaller than 5-mm in size. Microplastics can be classified as primary plastics, which are raw and manufactured at a small size (for example, microbeads), or secondary plastics, which are small pieces broken off larger pieces of plastic (for example, small chunks of plastic broken off a discarded bucket). Because many plastics are positively buoyant, they accumulate at the ocean’s surface.


Plastics associated with floating Sargassum habitat in the Gulf of Mexico.

“The only explanation which can be given, he says, seems to me to result from the experience known to all the world. Place in a vase some fragments of cork or other floating body, and give to the water in the vase a circular movement, the scattered fragments will unite in a group in the center of the liquid surface. that is to say, in the part least agitated.”

–Excerpt from Jules Verne’s book Twenty Thousand Leagues Under the Sea, 1873.

As Jules Verne describes so eloquently, any floating bodies in the ocean tend to group together in areas where water masses meet or physical ocean processes occur because of circular current movements. This means that both natural biological floating organisms or communities and man-made debris interact in the marine environment. One natural floating substrate that interacts with marine debris and floating trash is Sargassum, or Gulf weed.


“While sampling the pelagic Sargassum community in the western Sargasso Sea, we encountered plastic particles in our neuston (surface) nets.”

–Excerpt from an article, Plastics on the Sargasso Sea Surface, by E. J. Carpenter and K. L. Smith from the journal of Science, March 17, 1972.


Plastics found within the guts of fishes associated with Sargassum. Top: microplastic fibers. Bottom: blue chunk of microplastic.

Plastics have been evidenced in this floating algal community since the 1970s, but little is known about how plastics affect this community. Because this community is so diverse and supports a large number of fishes at varying life stages (larvae, juveniles and adults), there is potential for microplastics to have some kind of interaction with these associated fishes. These small pieces could be mistaken for food and be eaten which could potentially cause internal damage or possibly transmit anything attached to them such as toxins, bacteria, and maybe even viruses. Understanding interactions between microplastics, Sargassum habitats, and associated fishes can help us recognize what types of impacts microplastics could have on this diverse community.

Weedlines: A Sargassum Research Blog

PS-18-05 Daily Log

June 5, 2018 (Day 7)*

*Note: these will be posted on a one-day delay, i.e., this report is for yesterday’s activities.

We’re back in the Loop Current, aka, ‘life in the fast lane’. Things float just a little bit faster down here (including our research vessel!). Here is a short synopsis of some of the day’s activities.

Point Sur

A view of the R/V Point Sur during the small boat operations. (Photo: Courtney Stachowiak)

Today we started our search for Sargassum early in the cobalt blue waters of the Loop Current. Our heading ran perpendicular to numerous thin weedlines, but today we were hoping  to sample larger features, with an emphasis on collecting reflectance and backscatter data, and other optical qualities of Sargassum and open ocean habitats.During our search we spotted a large group of birds feeding in the distance, which is always a good sign. We changed our course to investigate, and soon we were surrounded by a dozens of sooty terns, calling and feeding along the Loop Current edge.


The CTD roesette at the surface during deployment.

There was relatively little Sargassum in the immediate vicinity, but on this new heading we soon found ourselves approaching some of the most concentrated patches of Sargassum we’ve seen so far during this cruise.



Mengqiu Wang  and Caitlin Slife measuring reflectance during the small boat ops. (Photo: Josh Bierbaum)


The remainder of the morning was spent collecting optical data from a smaller inflatable boat, as well as water samples from the Sargassum habitat. In the afternoon, we collected additional water samples, a CTD profile, and two neuston net samples through Sargassum weedlines. Similar to our visit to the Loop Current region last week, each neuston tow yielded very few Sargassum shrimp, crabs and associated fishes. Again, this is in contrast to our sampling in the more northern Gulf along the blue-green convergence weedlines. While Sabiki fishing we collected several juvenile Blue Runners and Almaco Jacks, and observed several large Mahi Mahi cruising the Sargassum patches.



The neuston net during deployment as seen from the small boat

Tomorrow is our last day of sampling before we set sail for home. We will ride the Loop Current treadmill tonight to stay in relatively the same location as we sampled today. New satellite imagery suggests another wave of Sargassum biomass is moving up the Loop Current and heading our way.

We’ll be waiting !!


Weedlines: A Sargassum Research Blog

PS-18-05 Daily Log

June 4, 2018 (Day 6)*

*Note: these will be posted on a one-day delay, i.e., this report is for yesterday’s activities.


The science team rinses the Neuston net. (Photo: Brian Jones)

Wanting to repeat our sampling along blue-green convergence lines, we stayed in the same general vicinity as the previous day’s effort. Here is a short synopsis of some of the day’s activities.


By morning, the “tide line” we sampled yesterday had moved south by several miles. Upon finding the blue-green water interface (which was not as distinct as yesterday), we started our sampling with a neuston tow through a series of Sargassum patches. The tow went very well, and was brought on board—just in time for a morning squall ! The science team worked diligently through the wind and rain, which lasted approximately 30 minutes or so.


The CTD and rosette sampler being deployed over the side of the vessel. (Photo: Glenn Zapfe)

The skies soon cleared and we deployed the CTD and rosette sampler to collect profile data and water samples. The brief storm sufficiently broke up the Sargassum patches, so we cruised further south to collect our open water samples (neuston net, water samples, reflectance, frame trawl, etc.). Again, sample collection went relatively smoothly as the sea conditions improved throughout the day.



Science team members Eric Haffey, Verena Wang, and Glenn Zapfe measuring the weight of a Sargassum sample.

With calmer seas we revisited our Sargassum station and observed the formation of new weedlines, which were mostly thin lines of small clumps. Yesterday and earlier today, we noticed that even these small clumps usually had several small fishes associated with them, so we decided to sample down the “skinny” weedlines. One of our interests is the relationship between fish abundances and the ‘morphology’ or shape of Sargassum features (mats, lines, and clumps). The neuston tow through this small series of clumps yielded our highest catch of the trip so far; we collected numerous juvenile Sergeant Majors, Orangespotted Filefish, Planehead Filefish, and Sargassumfish, among others. We continued our work in the Sargassum habitat into the early evening, with an additional neuston tow and reflectance measures.



Dr. Frank Hernandez and Valeria Nunez inspect the sample collected from the Neuston net. (Photo: Brian Jones)

So where to go now? Although we have a second cruise later this summer (in July), our colleagues from the USF Optical Oceanography Lab will not be able to join us for that trip. Therefore, we decided to prioritize the collection of additional reflectance and backscatter data for the remainder of this cruise while we had their expertise on board. New remote sensing analyses suggested that the Loop Current region we visited earlier still had very high Sargassum biomass, so a decision was made to return to that area. After cleaning up and securing our gear on the back deck, the vessel set a course for the Loop Current where we hope to continue our sampling success tomorrow.

Weedlines: A Sargassum Research Blog

Physical Oceanography

Now that you have become familiar with what Sargassum is and why it is important, we would like to provide you with some information about the physical oceanographic processes that contribute to the distribution and aggregation of Sargassum features.

Free-floating species of Sargassum are distributed throughout the North Atlantic, Caribbean, and the Gulf of Mexico. The distribution of Sargassum is influenced by mesoscale features such as currents, gyres, eddies, and fronts. In the North Atlantic, a large aggregation of Sargassum is formed by transport via the Gulf Stream and other currents associated with the North Atlantic gyre. Gyres are wind-driven currents that result in the transport of water in a circular direction in an ocean basin. In the Northern Hemisphere where floating Sargassum is found, these gyres rotate in a clockwise direction as a result of Earth’s rotation and the Coriolis force. The pattern of transport in these gyres follows the contours of land surrounding the ocean basin. The North Atlantic gyre transports Sargassum to the Sargasso Sea via mesoscale eddies, which are rotating water masses that separate from the large basin-wide currents. In the Sargasso Sea, early research estimated Sargassum covered approximately two million square miles. Sargassum is also transported by the Loop Current in the Gulf of Mexico and the Florida Current, which meets with the Gulf Stream in the North Atlantic gyre.

Sargassum Distribution.jpg

Map of Sargassum distribution and associated ocean currents.
(Source: http://ocean71.com/chapters/sea-like-none-other/)

Sargassum is also commonly found along frontal regions, where a boundary forms between distinctly different water masses. Convergent fronts of water masses result in the formation of Langmuir cells, where Sargassum is commonly aggregated into windrows. Langmuir cells are formed as water masses converge and are forced down into the water column at the boundary. The movement of water away from the boundary at depth then forces the movement of the water back to the surface. This transport results in the formation of rotating cells referred to as “Langmuir cells.”

Langmuir cells.jpg

Diagram of Langmuir cells formed by convergent water masses.
(Source: Tajada-Martinez et al, 2011.  J. Appl. Mech. 79(1))

All of these mesoscale features mentioned result in the formation of Sargassum clumps, mats, and weedlines. By understanding the oceanographic processes that transport Sargassum, we can predict where our sampling efforts will be most successful on our research cruises this summer.

Weedlines: A Sargassum Research Blog

PS-18-05 Daily Log

June 3, 2018 (Day 5)*

*Note: these will be posted on a one-day delay, i.e., this report is for yesterday’s activities.

After cruising north overnight we arrived at a location southwest of the birdsfoot  where we found Sargassum and environmental conditions to be very different from the Loop Current region. Here is a short synopsis of some of the day’s activities.

blue green.jpg

Sargassum is often found in the convergence zone, or tideline, of “blue” and “green” water. (Photo: Carla Culpepper) 

Overnight we steamed towards the north from our previous location within the Loop Current, and by morning, we quickly located a “tide line” (at approximately 26° 24′, 87° 50′) that extended for miles in a roughly east-west direction. Visually, we could easily distinguish the convergence of two water masses, with “green” water to the north of the weedline, and “blue” water to the south. This was further verified with the vessel’s flow-through system and thermosalinograph; we measured higher salinity and cooler temperature on the blue side, and lower salinity and warmer temperature on the green side. These conditions were similar to what we experienced last year in roughly the same area, but notably different than the past few days in the very “blue” Loop Current waters.

It was windy this morning, sea conditions were a bit rougher, and the currents associated with the convergence line made it difficult to navigate near the weedline without running it over. As such, the neuston net tow was less than ideal, as only half of the net was towed through the Sargassum line. Whereas the Sargassum collected in the Loop Current was more golden in color, “fresh” and free of biofouling, today’s Sargassum seemed “older”, with some senescence observed, as well as considerably more biofouling. Still, we got fish today, including a few Bermuda Chubs, Sergeant Majors, and Sargassumfish, as well as many Sargassum shrimps and crabs.

Lesser amber jack

A Lesser Amberjack collected during the small-hook Sabiki rig sampling effort. (Photo: Brian Jones) 

We collected water samples and reflectance data from both the green and blue sides of the convergence, then positioned ourselves for hook-and-line fishing with the small-hook Sabiki rigs. Within a few minutes, a small sea turtle (carapace length approximately 8-10 inches) appeared on the outskirts of the weedline. In an abundance of caution, we immediately reeled in all lines and allowed the vessel to drift away from the Sargassum. Once we were a safe distance away, we cruised further down the weedline and started a new fishing set there. Here we caught numerous juvenile Blue Runners (Hardtails), Greater Amberjacks and Lesser Amberjacks.


A juvenile Green sea turtle spotted near a Sargassum feature. (Photo: Brian Jones) 

A second juvenile sea turtle, roughly the same size, was spotted several hours later while the vessel drifted along the Sargassum while we were collecting additional reflectance measurements. As no gear were over the side, we maintained our drift for a few moments as the turtle continued to swim down the weedline.

After working the weedline, we cruised south to find “open” water, i.e., water free of Sargassum–which is turning out to be a very difficult thing! We moved 1-2 miles away from the weedline and still collected a few handfuls of Sargassum in the cod end of the neuston net. Similarly our frame trawl sample contained a small amount of Sargassum. It is likely that the windy conditions in the morning broke down some of the larger Sargassum patches, resulting in a “halo” of scattered Sargassum bits covering a wide area around the weedline.


Glenn Zapfe, Eric Haffey, Olivia Lestrade, and Valeria Nunez enjoy a few laughs while rinsing Sargassum. (Photo: Carla Culpepper)

All in all, a relatively successful day with Sargassum samples from a very different local environment. We will likely stay in this general vicinity tomorrow to continue sampling along blue-green tidelines, if possible.

Weedlines: A Sargassum Research Blog

PS-18-05 Daily Log

June 2, 2018 (Day 4)*

*Note: these will be posted on a one-day delay, i.e., this report is for yesterday’s activities.

Greetings from the Loop Current! Thanks to calm seas and plenty of Sargassum, we were able to get right to work after breakfast. Here is a short synopsis of some of the day’s activities.

Neuston 2

The science team hauls a Sargassum sample aboard the ship. (Photo: Brian Jones)

This morning found us in the Loop Current at approximately 26° N, 88° W, and in the midst of numerous weedlines. Conditions were somewhat similar to yesterday in that there were no large, continuous lines of Sargassum. Instead, there were long series of relatively large patches lined up along convergence slicks. We cruised around briefly looking for suitable sampling habitat and we were joined for a while by a large group (30-40) of what appeared to be Pantropical Spotted Dolphins (we are lacking in marine mammal expertise on board, so our best guess!). Finding a nice set of Sargassum patches, we got right to work, starting with a pair of short neuston tows. Again, we collected relatively few fish, which seems to be a theme for this area. While fishing with our Sabiki rigs, we collected a juvenile Rainbow Runner and a few juvenile Almaco Jacks. We observed numerous large Mahi Mahi swimming between the Sargassum patches, as well as a few unidentified triggerfishes feeding on the canopy edges.  It was a race to get any small fish we hooked onto the vessel while being chased by the Mahi. After collecting a few juveniles, we sampled a few of the larger fish, collecting blood, liver, and muscle tissue for stable isotope analyses, and the stomachs for diet analyses.

Sargassum associated fish.jpg

Two common Sargassum-associated fishes, the Planehead Filefish (left) and the Sargassumfish (right), both collected today. (Photos: Olivia Lestrade)

After lunch we set our camera system adrift in a Sargassum patch while collecting more reflectance and backscatter data, then we cruised to an ‘open water’ location and repeated our sampling ops. Interestingly, our frame trawl sampler, which we anticipated would collect juvenile fishes, came aboard with many larval fishes stuck to the cod end mesh. We noticed larval Surgeonfish (Acanthuridae), Tuna (Thunnus sp.), Triggerfish (Balistidae), and Squirrelfish (Holocentridae), among others. There were also many crab zoea and stomatopods, as well as a brown ‘film’ coating part of the net, possibly an indication of Trichodesmium, also called “sea sawdust” (a filamentous cyanobacteria).


Mengqiu Wang and Xingxing Han collect reflectance and backscatter data from Sargassum and open water habitats. (Photo: Josh Bierbaum)

After collecting some additional reflectance data at the open water location, we decided to steam back north towards the Gulf coast. Patches of Sargassum streamed by as we cruised along, reminding us of the considerable Sargassum biomass we observed in the Loop Current. Our goal for the next few days is to locate similarly productive sampling sites in different regions for comparison.

Weedlines: A Sargassum Research Blog

Sampling Gear

When designing a research project, scientists must decide which gear and equipment are most appropriate for collecting the data required to address their hypotheses. One of the main targets of our project are juvenile fishes, primarily those living in Sargassum habitats, but also juveniles in nearby “open water” habitats (in other words, water without Sargassum). Often times a single project may require multiple samplers, and that’s the case with our Sargassum research.

Sargassum is a floating brown algae, therefore a sampler than can be ‘fished’ at the water’s surface would be ideal. That’s why many Sargassum studies often rely on a neuston net. Neuston is a term that refers to organisms that live on or just under the surface of the water. Our neuston sampler has a 2-m wide by 1-m high rectangular opening, and a plankton net with a 0.5-mm mesh size. To collect Sargassum or any neustonic organisms, the net is fished half-in/half-out of the water. In open water, we tow the neuston net for 10 minutes, where it collects mostly larval fishes and small juveniles (bigger juveniles are usually too fast and agile, and often avoid the net). In Sargassum, our tow times are much shorter (less than 1 minute) because the net quickly fills up with Sargassum. In contrast to sampling in open water, the neuston net does a great job collecting juvenile fishes in Sargassum, because these small fishes seek refuge in the algae as the net approaches. So the neuston net is an effective sampler in both habitats, but often collects different fish life stages–larvae in open water and juveniles in Sargassum.


The neuston net fishing in “open water” (left) and in Sargassum (right).


The science team recovers the Methot frame trawl from its maiden voyage. Photo: Brian Jones

In order to collect the larger juveniles that evade the neuston net in open water, this year we will try a new sampler designed to collect these elusive fishes. The Methot frame trawl is a much larger net. The mouth opening is a square shape, approximately 2.25-m high by 2.25-m wide. The mesh size is larger as well, approximately 3-mm, and the net can be towed at a relatively fast speed, around 5 knots. Our hope is that the larger net mouth opening and faster tow speed will help us collect the juvenile fishes that usually escape our neuston net in open water. This is our first time using this sampler, and we’re excited to see what we get!

To maximize our sampling time at sea, we try to sample at night as well as during the day, which presents a new set of challenges. The main challenge is that once the sun sets, it’s nearly impossible to search for and distinguish between Sargassum and open water habitats. So at night we need to use a different strategy and different sampler. As the sun begins to set, we place a floating marker buoy with a flashing light inside a Sargassum feature to “mark” the habitat. Then, we steam away from the Sargassum to open water, and wait for the darkness. Now it is light-trap time! We place two of these samplers in the water where they float for approximately a half hour at the surface. A light is used to attract fishes through small openings (approximately 2.5-cm in diameter) that lead to a mesh “trap” compartment. Once retrieved, we locate our marker buoy and steam back to the Sargassum and repeat our sampling there. Light-traps are selective samplers, in that they generally collect juvenile fishes that are photopositive (attracted to light).

Light Traps.png

Light-traps prepped and ready for sunset (left) and being deployed in a Sargassm mat (right). Lights inside the mesh traps attract small fishes and juveniles which enter through tapered openings on the sides of the traps.


Researchers use small-hook Sabiki rigs to collect additional juvenile fishes. Photo: Glenn Zapfe

In addition to these methods, we also float a camera system in the Sargassum habitat to video the “undisturbed” fish assemblages, and hook-and-line sample with small-hook Sabiki rigs to collect additional juveniles. By combining multiple gear types, we hope to better categorize the juvenile fish assemblages associated with these different offshore habitats.


Weedlines: A Sargassum Research Blog

PS-18-05 Daily Log

June 1, 2018 (Day 3)*

*Note: these will be posted on a one-day delay, i.e., this report is for yesterday’s activities.

Frank Hernandez

Dr. Hernandez scanning the horizon for signs of Sargassum (Photo: Carla Culpepper)


Today we woke up along the northwest edge of the Loop Current (approximately 26° 38′ N, 88° 19′ W) and quickly found patches of Sargassum in the area. Here is a short synopsis of some of the day’s activities.


Dr. Dillon uses a Horizontal Niskin Sampler to collect water near a Sargassum patch. (Photo: Glenn Zapfe)

Sargassum was plentiful in our region, though again we did not find very large mats or weedlines. Multiple lines of surface convergence were observed, and along these frontal features were rows of smaller Sargassum clumps with an occasional larger patch (5-10 m long) interspersed in between. After searching for a few hours, we decided to sample a set of these larger patches. Sunny skies allowed for good reflectance measures; the CTD cast and water collection proceeded smoothly. During these ops, we did not see many fish associated with the Sargassum mats, and our fish collecting ops confirmed this.  Our neuston net pulled in a large of Sargassum, approximately 143 kg (that’s over 300 lbs)! It took the better part of the day to procss this much algae. In spite of this high biomass collected, there were very few fish present: we found a few juvenile Sergeant Majors and Tripletails (but little else).


A juvenile Tripletail (Lobotes surinamensis) collected in a neuston net towed through Sargassum. (Photo: Frank Hernandez)

Today we deployed our camera system for the first time within a Sargassum mat; this is a simple camera set up with 2 GoPro cameras filming under the Sargassum canopy. Scanning through the video, we again saw only a few fish over the course of 30 minutes or so (Tripletail, Amberjack, among others). Lastly, we sampled using hook-and-line fishing with Sabiki rigs, and collected a pair of Hardtail juveniles and several juvenile Almaco jacks (4 anglers fishing for 30 minutes). We were able to collect blood, liver and muscle tissue samples from these larger juveniles for later stable isotope and protein/fatty acid analyses.


R/V Point Sur Marine Tech Josh Bierbaum, Ph.D. student Mengqiu Wang, and Dr. Xingxing Han deploy small boat ops to collect data from a Sargassum patch. (Photo: Olivia Lestrade.)

In short, all of our sampling gear indicated the same result today–just not many fish associated with Sargassum in this region today. It’s difficult to speculate why at the moment, but one of our objectives is to examine spatial variability in Sargassum-associated fish assemblages, so these data, along with the environmental data (salinity, temperature, etc.) will prove very useful.

Today we also deployed a small boat from the Point Sur to get “up close” measurements of reflectance and backscatter from Sargassum and open water habitats. This worked very well–a special thanks to Mengqiu and Xingxing for adding this new set of observations to the project! We may use the small boat again in the coming days to collect these and other in situ measurements.

So our first Sargassum habitat sampling was a success, even though it was “light” in the fish department. We hope for continued calm seas and golden algae in the days to come!