Ocean fertilization and climate change

By Yonara Garcia

Have you heard of geoengineering? It’s a tool becoming increasingly used, but is often controversial because, in some cases, the result can be completely unexpected!

Today we’ll talk about a polemic experiment carried out in July 2012 by Russ George, an American businessman who dumped approximately 100 tons of iron sulphate in the Pacific Ocean as part of a geoengineering project off the west coast of Canada (http://www.nature.com/news/ocean-fertilization-project-off-canada-sparks-furore-1.11631).

Ocean fertilization by iron sulfate. Source: http://officerofthewatch.com/2012/11/05/canada-iron-fertilization-incident/

Iron is considered an essential element, often limiting, for phytoplankton growth. Phytoplankton perform photosynthesis, a process in which sunlight is used as an energy source and absorbs carbon dioxide (CO2) and water to produce organic matter in the form of carbohydrates. Phytoplankton cells are formed from these carbohydrates with the addition of other substances such as proteins, amino acids, and other molecules.

In 1980, oceanographer John Martin proposed that certain regions of the ocean (the areas called HNLC - High Nutrient, Low Chlorophyll), although rich in nutrients, would be poor in primary production due to lack of iron. Thus, the addition of iron should increase the production of phytoplankton and hence affect the carbon cycle, reducing CO2 levels in the atmosphere. His famous phrase “Give me half a tanker full of iron and I’ll give you an Ice Age” caused great excitement because he believed that if certain areas of the ocean were fertilized, the effects of global warming could be reversed, cooling the Earth.

Thus arose the idea that the American businessman put into practice. Russ and his team released a certain amount of iron into the sea, believing it would promote photosynthetic activity and thus increase the efficiency of the carbon sequestration processes in the ocean. Just like the process to fertilize a crop for it to go grow faster! This issue has generated much controversy because it conflicts with ethical and political questions about the effects that an intervention like this would bring to a complex ecosystem. We still know relatively little about the ocean. To better understand why the idea of this project is so controversial, let’s first talk about some important processes in the “wonderful world ocean.”

Have you ever heard of “physical pump”? Or a “biological pump”? No, it’s not a kind of weapon of war to decimate an enemy population. The physical pump is the process related to the solubility of CO2 in the ocean (solubility = maximum amount of a substance that can be dissolved in a liquid). The biological pump takes into account what happens to the CO2 after it is dissolved in the ocean, when a fraction of dissolved carbon is absorbed through photosynthesis, in the surface layers of the ocean, and transported to the bottom. The diagram below explains how carbon is transported in the ocean.

Carbon movement in the ocean system. 1) Using solar energy, carbon dioxide is fixed by phytoplankton in the photic zone (where there is light). 2) Part of this organic matter is consumed by zooplankton and some heterotrophic microorganisms. 3) Other organic matter is exported from the photic zone toward the mesopelagic zone (about 1000 m deep), and a fraction of this organic matter is remineralized while the rest goes to the bottom of the ocean, where it will take thousands of years to return to the surface. Adapted from United States Joint Global Ocean Flux Study.

CO2 is a gas capable of dissolving in the surface of the oceans. This solubility mechanism is related to the concentration of this gas in the atmosphere and the water temperature: the more CO2 in the atmosphere and the lower the temperature, the greater the amount of gas dissolved in the ocean surface. Once dissolved in water, the CO2 passes to a further stage of the cycle, where it can be absorbed by photosynthetic marine organisms.

Part of the organic matter formed during photosynthesis is used in cellular respiration and released back into the seawater as CO2. The other fraction, which was used in the formation of the cell, is consumed by zooplankton (primary consumers in marine food webs - read more here) and/or transported by gravity to the bottom of the ocean through  “marine snow,” particles made up of food debris and fecal pellets coming from feeding zooplankton, shells, and dead microorganisms. This carbon transfer process to the deep ocean decreases the amount of carbon in the photic zone (zone that receives enough sunlight for photosynthesis to occur), sequestering (removing) billions of tons of carbon from the atmosphere each year. Some studies have estimated that the biological pump is responsible for removing about 5-15 gigatons of carbon per year (Henson et al., 2011).

Marine Phytoplankton. Source: http://www.smithsonianmag.com/science-nature/vanishing-marine-algae-can-be-monitored-from-a-boat-with-your-smartphone-2785190/?no-ist

You can probably imagine how important this removal is when looking at the large amount of carbon that our industrial activities, cars, and planes have emitted into the atmosphere over the last few years. It is important to remember that the much discussed global warming, among other issues, is largely caused by an excess of carbon in the atmosphere. According to the IPCC (Intergovernmental Panel on Climate Change) 2014,  in 2010 alone, 49 gigatons of carbon were released into the atmosphere by human activities. And that is precisely why these experiments with iron have gained so much popularity.

Sounds simple, right? Okay, solved the problem of global warming! Let's fertilize the oceans! But it is not so simple. Interfering in natural ecosystems is an extremely sensitive subject, which can cause incalculable and irreparable damage.

Some researchers performed similar experiments as the American businessman and concluded that despite the fertilization increasing the rate of photosynthesis, it can trigger changes in ocean chemistry by changing the operation of the entire system. For example, increased photosynthetic rates by phytoplankton are directly proportional to the amount of dimethylsulfide (DMS - volatile sulfur in reduced form) secreted by these microalgae in water, which is vaporized and form condensation particles in the air (i.e. more photosynthesis by the phytoplankton = more dimethylsufide into the air). In the atmosphere, these particles facilitate the formation of clouds, which would be great, because with the increased formation of clouds there is increased reflection of solar radiation and thus greater cooling of the planet. However, not all types of clouds have the property to cool the planet. Recent studies suggest that other climatic factors may also affect the distribution and properties of clouds, which could increase the temperature of the planet. Furthermore, it was observed that fertilization also increases the production of nitrous oxide (N2O), a molecule that heats 320 times more than CO2.

Another study, published in April 2014 in Geophysical Research Letters, showed that more than 66% of the carbon sequestered by the ocean returns to the atmosphere in 100 years. That is, the biological pump may lessen the temperature of the Earth, sequestering carbon from the atmosphere, but we do not know what will happen when this carbon returns. Controversial enough for you?

Image obtained by NASA, satellite view of a phytoplankton bloom.

Thus, although the processes that occur in the ocean are responsible for reducing the concentration of CO2 in the atmosphere, altering the system may not be the best solution because there are many chemical, physical, and biological processes that are not fully understood. While we did not reach a more integrated understanding of these processes, the reduction of CO2 emissions would be much more efficient and safer than trying to remedy a problem by manipulating a process so complex and poorly understood.

Literature:

http://www.nature.com/ngeo/journal/v6/n9/full/ngeo1921.html

http://www.nature.com/nature/journal/v446/n7139/full/nature05700.html

https://www.ipcc.ch/publications_and_data/ar4/wg1/en/ch7s7-3.html

http://onlinelibrary.wiley.com/doi/10.1002/2013GL058799/full

https://www.ipcc.ch/pdf/assessment-report/ar5/syr/AR5_SYR_FINAL_SPM.pdf

Henson, S. A., R. Sanders, E. Madsen, P. J. Morris, F. Le Moigne, and G. D. Quartly (2011), A reduced estimate of the strength of the ocean's biological carbon pump, Geophysical Research Letters, 38

Diving for life in the darkness: a survey of the deep

By Camila Negrão Signori

Just being involved in a scientific expedition aboard the R/V Atlantis (managed by the prestigious Woods Hole Oceanographic Institution, WHOI) was itself an enriching experience. I was no stranger to ship research, having crossed the South Atlantic from Africa to Brazil, been to the continental shelf of the southern and southeastern coasts of Brazil, and sailed three times in the waters of the Southern Ocean surrounding the Antarctic Peninsula, but my experience on the Atlantis with the submersible Alvin was quite a different experience. 

Photo 1: Alvin being prepared for its decent, with two divers on top and a boat in the water to offer support. (Photo by Camila)

This experience was only possible by an invitation by my collaborator Dr. Stefan Sievert who had helped develop part of my PhD research with polar samples in Woods Hole (funded by CAPES-Training Coordination of Higher Education Personnel). Stefan was the scientific coordinator of this cruise with a project funded by the US National Science Foundation (NSF) entitled “Integrated Study: metabolic energy, carbon sequestration, and colonization mechanisms in chemosynthetic microbial communities in deep hydrothermal vents.” My job was to help Stefan and Jesse McNichol (my friend and doctoral student in the MIT-WHOI joint program) in all on-board tasks. 

There are many reasons this was such a different experience from my other times at sea. This was my first time in the Pacific Ocean. It was my first time aboard a ship run by a research institute, and it had a greatly reduced crew of about 25 (the other ships I have been on have been run by the Navy of Brazil, manned by 50-60). This was an international ship, with 23 researchers from countries including the United States, Canada, Germany, Italy, Spain, Japan, China, and myself from Brazil. 

Instead of navigating to different oceanographic stations (to spatially explore physical, chemical, biological, and geographical oceanographic features), we remained in the same sample area of 9 degrees N for almost an entire month. Our landscape was an expansive ocean without an end in sight, and we were a 4-5 days steam from the nearest land. The objectives of the project were all related to the deep ocean, at hydrothermal vent sites. 

Photo 2: Camila Negrão Signori observing life in the deep ocean through one of Alvin’s five portholes (Photo by Stefan Sievert).

Typically, water is collected from different depths, selected according to differences in water mass through the layers of the ocean, using a Niskin bottle, usually coupled to a CTD-rosette system. However, for this journey, we used the famous submersible Alvin, diving daily to more than 2500 m deep to collect our samples. With the help of two robotic arms and a “biological basket” able to carry more than 180 kg of bottom material, we collected samples such as fluid from the vents, microorganisms associated with the sources, invertebrate worms, and near-vent settlers. 

Instead of using water collected by Niskin bottles on board the ship, we collected fluids for chemical and microbiological analysis with a special piece of equipment known as an Isobaric Gas Tight sampler (IGTs). These IGTs were developed by WHOI to maintain pressure and environmental conditions of the deep when brought to the surface. 

Photo 3: A “IGT” sampler collecting fluid with the help of a robotic arm. The fluid here was 25C at 2500 m depth, collected at the “Crab Spa” location. Crabs, bivalves, annelids, and microbial mats can be seen here. (Photo by Camila, C WHOI).

Despite calm seas, work in the ship’s lab with the samples was not a trivial task. When removing fluids from the IGTs, we needed to be extremely careful with the high-pressure samples when opening and closing the system. Work was done with tools I had not seen before, and this was often morning and night work (after the Alvin returned to the ship). It was very difficult to draw out 150 mL of hydrothermal fluid and then continue with traditional laboratory protocols such as DNA extraction of microorganisms, gas measurement (such as Hydrogen sulfide), measurements of chemosynthesis processes, counts and cultivation of microorganisms, and incubation experiments using different temperatures and nutrient additions. 

Having the chance to dive so deep was one of my dreams (I thought impossible), but it became a reality on November 14th, 2014. 

Once the Alvin was released into the water from the giant cable it had been suspended from off of the Atlantis, we felt a slight swing in the surface waters of the Pacific. After a last check by two divers on top of the submersible and a brief goodbye and good luck wave through the portholes, we started our descent to the deep sea. 

The first 100 m of the water column were a beautiful turquoise color, but shortly after crossing the 300 m depth, everything became completely dark and quiet. As we passed the Oxygen Minimum Zone (300-800 m), bioluminescent organisms appeared floating in contrast to the black water. After a very gentle hour and a half descent (it felt like I was sitting on a sofa!), the pilot, Phil Forte, turned on the Alvin LED spotlight and a new world appeared under my eyes. 

Photo 4: Hydrothermal source with black smokers in full swing, under the sea. 2514 m deep, observed through the Alvin porthole. (Photo by Camila, C WHOI)

We landed on the seafloor, which was made up of ocean bottom ~200 million years old and some basaltic rock that shone brighter, indicating a more recent formation of a typically more active area. And so, with the help of our GPS, we began to explore the study area for six hours. After another hour, we had returned to the surface.

From all of the scientific papers, pictures, videos on the internet, and stories from those who have plunged to these hydrothermal vents in the Pacific, I expected I would find a bounty of life. But deep down, we always have that nagging in our heads…is this real, did these people actually see these things? 

And yes! We did see an abundance of life in the deep ocean: many small white crabs that justify the name “Crab Spa”; invertebrates including the annelid Tube worm, a species of giant tube worm that can reach nearly 2 meters in height with reddish color at the tips from the hemoglobin complex adapted to the sulfides present, toxic for us humans; 30 cm long, blind, albino fish swimming about resembling eels with their lack of scales (called Eel pout). We also saw yellow bivalves, small shrimp, and lobsters in the area in addition to the famous microbial mats. 

Photo 5: Dr Stefan Sievert (left), pilot Phil Forte (center), and Camila Negrao Signori (right) in Alvin’s sphere 2514 m deep. (Photo by Camila).

I must confess however, that, although a researcher of microbial oceanography, what impressed me the most was the geological structure that seemed artistically carved, surrounded by black smokers rich in metal sulfides. It was simply stunning to see this “step” in the ocean crust, where the Earth was being newly formed, and life abounded. 

How did I feel after the dive? Well, aside from my amazement at the excess of life and beauty, appreciation for the technology we have developed to explore these new frontiers, and how blessed I felt to have experienced this opportunity with such a great international group of competent people, I felt very little. As small as a drop of water in the vast ocean or a tiny bacterium shining under the microscope! We still have much to learn about the mysteries of the sea. 

Photo 6: A group of scientists embarking on the R/V Atlantis, opposite the Alvin garage. (Photo by Camila).

Dive 4769: an experience I will never forget! Sometimes when I find myself thinking about this dive, it pains me to believe that I was there at one time. I am extremely grateful to Dr. Stefan Sievert, who trusted in my work and gave me this chance to ride and learn on board the Atlantis and Alvin. I also thank all of my fellow scientists and competent crew, for sharing this experience with me and for all of the efforts and hard work put in to break into life in the dark. 

For more information, check out the links below:

Expedition blog “Dark Life” to the hydrothemal vents of the East Pacific Rise: http://web.whoi.edu/darklife/
About Woods Hole Oceanographic Institution: http://www.whoi.edu/
An overview of my research career: http://agenciasn.com.br/arquivos/3010

About Camila Negrão Signori:
Oceanographer, Master in Biological Sciences/Zoology, and PhD in Sciences/Microbiology, with periods of comings and goings to WHOI (USA). Born in Campinas (Sao Paulo), but has been enchanted by the sea since a childhood spent in Ubatuba Bay. In her spare time, she loves sports and dance, is always surrounded by family, her boyfriend, and wonderful friends. Today she is a Post Doctoral researcher at the Oceanographic Institute at Sao Paulo (USP) and a member of the microbial ecology laboratory where she researches the effects of climate change on microbial communities of the Southern Ocean. 
Contact: camisignori@hotmail.com

Primary producer dynamics and deep convective overturn in the Mediterranean Sea: a 3D high resolution modeling approach

By Fayçal Kessouri

My work focuses on modeling plankton ecosystems using a physical-biogeochemical coupled model. This kind of modeling is a 3D virtual representation of the main constituents of the lowest trophic level of a marine ecosystem. It includes plankton, bacteria, and the nutrients that support them under realistic hydrological conditions and atmospheric forcing.

The biogeochemical model I use shows the impact of current dynamics on the nutrients that support the marine plankton including nitrate, phosphate, and silicate. How are they distributed in the ocean? How are they consumed? Who consumes them?

The biogeochemical model shows only a part of the complex feedbacks between different components of the ecosystem. Some examples are as follows and are shown in figure 1 below: inorganic matter feeds the phytoplankton when certain abiotic conditions are available (enough light, stratified ocean layer), phytoplankton feed zooplankton, both of them produce organic matter. Organic matter is mineralized to inorganic matter, which then feed bacteria, which release dissolved inorganic and organic matter, and the cycle continues.

Figure 1: These biogeochemical feedbacks between compartments take place in the ocean. (POM= particulate organic matter, DOM= dissolved organic matter, DIM: dissolved inorganic matter or nutrients).

Marine plankton are the foundation of all marine life. They influence fisheries, the world economy, and world health, and they have an important role of maintaining biodiversity. Plankton are composed of:

1- The phytoplankton: which contain the largest mass of marine plants in the world. Some estimates show that marine vegetation produces more than half of the oxygen we breathe on Earth.

2- The zooplankton: which feed on phytoplankton (see also Catarina’s post). They represent the largest diurnal animal migration in the world.

3- The bacterioplankton and virioplankton: making up the largest biomass on the planet, prokaryotes and viruses are often a forgotten aspect of classic marine food webs.

The Mediterranean Sea lies between three continents (Europe, Africa and Asia) and therefore undergoes physical pressures from river discharge and atmospheric deposits of inorganic and organic matter, which has two levels of impacts: (1) overall balance of organic and inorganic matter in the whole sea, (2) eutrophication of coastal waters.

One of our most important findings using this modeling is the quantification of all imports and exports of matter during the last ten years between the Mediterranean and the surrounding environments (continents and Atlantic Ocean). We have estimated that the Mediterranean enriches the Atlantic by more than 140 X 109 moles of nitrogen every year through the Strait of Gibraltar.

The Mediterranean Sea has a common feature with the North Atlantic Ocean and the Antarctic Ocean: deep convection zones. In the Mediterranean, intense mixing is observed almost every winter for two months. Imagine a drop of water moving from the bottom of the Mediterranean at a depth of 2300 m and rising to the surface in a single day. This convective overturn from the gradients created by exchanges in surface heat and freshwater fluxes is the engine of global oceanic thermohaline circulation. This density-gradient driven circulation is estimated to be on the timescale of 70 years in the Mediterranean and 1000 years in the world ocean.

The deep-water masses contain high concentrations of nutrients, which are propagated to the surface during the deep mixing events. When the mixing stops at the end of winter, some of these nutrients are trapped in the surface waters, and a huge plankton bloom occurs over an area of 5 000 to 20 000 km2 (figure 2). Phytoplankton blooms can be so large, many can be observed and estimated from space by Satellites, and are thus well modeled. The phytoplankton bloom takes directly above the site of deep convection, which is referred to as the northern gyre of the NW Mediterranean Sea. They gyre is surrounded by strong cyclonic currents (counterclockwise in the Northern hemisphere).

Figure 2: Modeled phytoplankton concentration (chlorophyll-a [mg/m3]) in the NW Mediterranean Sea. a- Winter condition, the center of the basin is phytoplankton deplete because of winter vertical mixing. b Spring phytoplankton bloom (Kessouri et al., in prep).

Fayçal Kessouri

I am currently a postdoc in the Ocean and Atmospheric department at the University of California in Los Angeles, CA, USA, and my Ph.D. was developed at Toulouse University in France (Laboratoire d’Aerologie). My field of work is oceanic biogeochemistry and 3D modeling of plankton ecosystems, especially oceanic physical forcing. I worked on the deep convection of the Mediterranean Sea impact on the plankton ecosystem, and currently I am working on the upwelling of the California Current System and its impact on acidification and hypoxia of the western US coast. My desire to get training in numerical modeling motivated me to work with a team of physicists to acquire a more integrated vision of ecosystem functioning and impacts. It has helped me to study dynamic processes such as the deep convection that has always fascinated me. I am convinced that modeling is the perfect tool to complement the networks of observations currently being made, especially if one wants to study different time and space scales.

  

Fishers’ stories

By Ana Helena Bevilacqua

Everything started in 2007, when a São Paulo girl left her hometown to live on the Amazon. The main objectives were to get a master’s degree, study freshwater fish physiology, get to know the forest, learn how to fish, and to spread her wings. She achieved all of these things, fishing abilities left to be desired…

The master’s project fieldwork required long periods of time spent in the Amazon’s countryside, collecting fish, doing experiments, meeting people, learning the local customs, and living intensely with the forest and its traditions. And in the middle of this ocean of new experiences, a passion for the anecdotes told by fishers arose!

At the time, the stories were not the goal of the study, but they quickly became a personal goal. Long, late afternoons were spent together with fishermen and their families, with many kids, dogs and, for sure, a good cup of sweet, fresh coffee, a local tradition not to be missed!

From these relaxed chats, was born ideas for a future PhD. Until this point, the PhD was merely a faint idea since the master’s degree needed to be finished first. As time passed, the fieldwork was finished, the master’s degree was defended, and the will to continue the talks was only increasing. But what was next?

But there, a PhD topic had already been mapped out: human ecology of small-scale fishers!

And so, the migration to the marine sciences happened as naturally as those long conversations on the riverbank. Giving way to more targeted conversations, accompanied with only clipboard, paper, pencil, and a huge salt-water ocean ahead.

The perfect life: go to the beach to spend all day talking with fishers! This is all that I wanted! But, there was more to this, I had an ultimate goal, so the conversations were not uncommitted and light. There were questions to be answered, a methodology to be followed, and something to be done. After all, it was PhD fieldwork!

The goal of my PhD was to understand a little more about the small-scale fishers from the northeast coast of Brazil, and communicate traditional fishers’ knowledge to the scientific community. Basically what I wanted to do was to combine the fishers’ stories with traditional knowledge of marine sciences, and show that this knowledge can fill the gaps in scientific information in areas with limited data available. This information from local fishers could be used in sculpting local management plans and public policies. However, this first required me to prove that there is knowledge and truthful information behind the fishers’ anecdotes. 

I needed to compare the information provided in the fishers’ stories with the information from scientific literature, which I did using a marine ecosystem virtual model. This virtual model tries to represent all ecological relationships that exist in the real ecosystem, such as growth, reproduction, and predation. For this, I built two models: one based on scientific information and another one based on my conversations, and then compared the two!

For this ecosystem model I used free software called Ecopath with Ecosim, which is a computational program where we can insert all the information of a real environment and to create a virtual one. This software was created by Villy Christensen and Daniel Pauly in 1992, at the Institute for the Ocean and Fisheries (ex-Fisheries Centre), in the University of British Columbia, in Canada, and is constantly being enhanced. The program I use is based on energy balance equations that define the natural dynamics present in the marine environment and the ecological interactions that occur there. In other words, all energy available is cycled between all species, and is responsible for organismal growth and reproduction. For this, we use information about how much food predators require and compare this to production rates of the prey. The program is able to create an “ecological snapshot” about what is happening in that environmental (if you want know more about this software, go to ecopath.org).

For the construction of a virtual marine ecosystem (or freshwater, if you prefer), we must define the area, insert all species or groups of species, include information about the diet of each organism, determine the predators, how much food each one needs per day and growth rates. Of course we also must include the fisheries, by vessel type and gear.

After this, the software can use the biological interactions to create a trophic web of who eats whom, just like the diagram below. The advantage of this model is that in addition to creating an easy visualization ecosystem, we can change fishing pressure on target species, and also include the by-catch (common expression in fisheries science to define the species that was caught unintentionally).

This food web was created using Ecopath with Ecosim software, using only the fishers’ information. The color indicates the trophic level: in red are the producers at the bottom of the ecosystem (seaweeds, phytoplankton, and detritus), and blue is the highest trophic level, represented by predators (shark, dolphin and large pelagic). The circle size represent the biomass (amount of individuals or weight of each group) and the lines represent the links between each group.

The best thing about this model is that we are able to “predict” how the entire ecosystem would react to an increase (or decrease) in fishing pressure, restriction of certain gear, creation of non-take zones, or even a total ban on fishing. With that, we can have a better understanding of future fish stocks, if a number of management and conservation actions are (or not) taken.

And what about the fishers? The results were amazing: the fishers model is almost the same as the scientific model! This means the fishers’ knowledge can be equated with scientific knowledge on some issues, and this can be used to fill the gaps about areas or species with little to no current scientific data. Furthermore, this knowledge is cheaper and more quickly accessible than most scientific research. 

Of course, the fishers don’t know everything. Some questions they were unable to answer. Just like in science, some issues remain a mystery for mankind. 

Thus, combining science with traditional knowledge of natural resources, we can gain a better understanding of ecological relationships and facilitate the implementation of management plans.

All photos by: Laura Honda.

More information in: 

www.ecopath.org

Christensen V (2013) Ecological networks in fisheries: predicting the future? Fisheries 38(2):76–81
Christensen V, Pauly D (1992) ECOPATH II—a software for balancing steady-state ecosystem models and calculating network characteristics. Ecol Model 61:169–185
Coll, M., et al. (2015) Modelling dynamic ecosystems: venturing beyond boundaries with the Ecopath approach. Reviews in Fish Biology and Fisheries 25.2: 413-424.

About Ana Helena Bevilacqua:

Ana was always in love with animals, but it was the fishes that most caught her attention. Since she hated see sick animals, she decided to be a biologist (Mackenzie University, São Paulo), and later went to the Amazon to do a masters’ degree (National Institute for Amazonian Research, Manaus) and ended up going to the beach for her PhD studies. Today, Ana is freezing in Vancouver (Canada), where she is doing an exchange as part of the PhD requisites in Ecology, in the Federal University of Rio Grande do Norte (Natal). In addition to animals, she is interested in healthy eating, canine psychology, hikes, stand-up paddleboard and maracatu.

The hard-knock life of a marine baby fish

By Cássia G. Goçalo

Most fish in the world’s oceans reproduce by releasing their reproductive cells (oocytes and sperm) into the marine environment, where the two meet and fertilization occurs. Fish like sardines, groupers, tuna and cobias use this strategy to spawn millions of eggs. About 24 hours after (more or less, depending on species) the end of embryonic development, baby fish are hatched, called larvae.

Eggs and larvae of fish

For a tiny larva to survive in the marine environment, a large amount of quality food is necessary (such as zooplankton, see "For plankton, size matters"). Babies need to be well fed to guarantee fitness and growth until they reach adulthood. In the ocean, there are many animals that feed on small organisms, and eggs and fish larvae have high nutritional value. Fish and other marine animals, such as jellyfish, consume millions of eggs and larvae each season, as just another step in the marine food chain.

Jellyfish Liriope tetraphylla capturing a cobia larva (Rachycentron canadum) 5 mm in size.

It was once believed this little fish lived floating in the seawater for days or even weeks until its eyes, mouth and fins were completely developed. In my doctoral project, I studied the behavior of these small larvae during the first days of life, and I observed that, in addition to floating, they have an amazing swimming ability. Larvae are able to achieve extremely high speeds while swimming to capture food, up to 40 times their body size per second. Note: the world’s fastest man swims only 1.5 times his body size per second!

In general, the swimming of marine organisms is related to feeding, breeding, and the escape from predators. To get food, fish larvae need to coordinate their bodies to move their fins, interpret prey movement, open their mouths, and then capture the prey. To get away from predators, they need to bend their bodies and change swimming direction to successfully escape. These behavioral patterns were recorded for grouper (Epinephelus marginatus) and cobia (Rachycentron canadum) larvae, in my studies. To perform this research we (Laboratory of Plankton Systems team and me, http://laps.io.usp.br/index.php/en/) set up an optical system with a similar configuration to a microscope but in a horizontal position, to study organisms 2-5 millimeters in size in a small aquarium. We filmed with a video camera that captures a high rate of frames per second (also known as "high speed camera"). See more at https://www.facebook.com/lapsiousp

Even with all this skill, survival rate of individuals is only 1% from egg to adulthood. This high mortality rate is due to predation and/or starvation. A small larva faces many challenges, but if successful, one day it will become a mature adult fish and produce a new generation of eggs and larvae, maintaining a natural balance between species and the marine ecosystem.

In the marine environment there are about 16,000 species of fish, many of which we know little about the larval behavior of. An example similar to the research done in my doctoral work is the study conducted on adult fish behavior through, which can be seen in documentaries presented by the National Geographic Channel (http://natgeotv.com/uk/hunters-of-the-deep/galleries/super-fast-fish ). The researchers offered different prey and filmed the swimming and feeding behavior of different species of marine fish. For the curious: access the page and watch the video "Blink of an Eye."

Questions and comments? Contact us or leave a response below!

See you on the next post!

References:

FUIMAN, L. A. Special considerations of fish eggs and larvae. In: Fuiman, L. A.; Werner, R. G. (eds). Fishery Science: The unique contributions of early life stages. Blackwell Science. p. 1- 32, 2002.

GOÇALO, C.G.; AQUINO, N. A. de; KERBER, C. E.; NAGATA, R. M.; LOPES, R. M. Swimming behavior of cobia larvae (Rachycentron canadum) facing prey and predator. 38th Annual Larval Fish Conference, Quebéc, Canadá. 2014

HOUDE, E. D. Emerging from Hjort’s shadow. J. Northwest Atl. Fish. Sci., v. 41, p. 53-70, 2008.

Labels: Cassia G. Goçalo, Marine Science, behavior, fish larvae