The adventures of Fred the copepod

During the next days I will be posting something very different, a child’s story. The project intents to reach the youngest audience with a story about a copepod named Fred that explains, in an educational and entertaining way, what copepods are, what they do in the sea, and the problems he experiences during his life. He introduces concepts such as predation, reproduction, vertical migration, and pollution and presents other components of plankton, such as microplankton andmeroplankton. The ultimate goal is to make children and adults aware of the fragility and importance of plankton and the need to take care of the sea. The original book has two levels of reading: one designed for children from 6 years old and another for adults who want to know more about marine plankton. This dual way of providing information will reach a much larger audience. Here you have the first pages. Next pages, soon! Enjoy.

This was the last entry of my kid’s story. I hope you enjoyed it and read it to your kids to raise awareness about the fragility of the ocean and the need to take good care of it. And, if you know someone that wants to publish it (either in English, Spanish, or Catalan), let me know ūüėČ

Microplankton and Metazooplankton from the Catalan Coast, December 15th, 2022

In these 3 videos you will find a summary of the most relevant findings from PUDEM sampling in front Barcelona. The community was rather surprising, because it seemed an end of summer one, with cladocera (Penilia avirostris and Evadne spp.) and Oithona spp. combined with a diatom bloom of very large and diverse species. I guess this community reflects the unusually warm temperatures we had this year.

I highlight the presence of the pennate diatom Bacillaria paxillifer that forms colonies in which adjacent cells glide using filamentous structures. 

The fragility of plankton

When there is a natural disaster at sea, such as the Exxon Valdez in Alaska (1989) or the Prestige in the NW Spanish coast (2002), we all immediately worry about seabirds, turtles, and dolphins and how the disaster will affect fisheries. On television, we are flooded with images of black birds, covered in oil, and dead fish on beaches. All of this is relevant and important, of course. However, no one (apart from three or four specialist scientists in the field) stops thinking about what effect it can have on the base of the food web, the plankton. We are not aware of the fact that if the plankton fails, the house of cards collapses, and we can forget about the birds, turtles, dolphins, and fish because nothing will reach them to eat and they will die irretrievably. Fortunately, although certain groups of plankton are very sensitive to hydrocarbon pollutants, the dilution effect of seawater and the mostly superficial zoning of the crude play in their favor.

It does not take a natural catastrophe to harm plankton. Fully accepted anthropogenic activities also have an effect. For example, if someone proposed cutting down an oak forest to plant exotic fruits, such as passion fruit, papaya or others, we would react by calling it an ecological monstrosity. Yet, if the case was a foreign species of oyster (like those that populate aquaculture facilities, mostly originated in the Pacific), in a bay where we do not swim, it probably would alarm no one. However, these crops destroy planktonic diversity and damage the entire marine ecosystem around them. Besides filtering a good part of the plankton present, they pollute the water and the sediments to the point of producing anoxia. If that was not enough, they are also hotspots for jellyfish and harmful algal bloom proliferations. All in all, a real ecological disaster that we completely ignore.

Mediterranean plankton

Plankton are very sensitive to pollutants, and many studies support this. I do not want to get into technicalities and flood you with data on the effect of mercury, cadmium, chromium, etc., or what are the consequences of sunblock creams or medicines that end up in the sea. What I will tell you are two anecdotic examples that I have witnessed and which were not part of any specific study, but which undoubtedly reflect the fragility of plankton.

The first example dates back to my time as a Ph.D. student, when I started growing copepods in the laboratory. To keep these small crustaceans, we used seawater filtered through cartridges with different filters. I remember once the plastic connecting screw between two cartridge holders was damaged, and we replaced it with a copper/bronze one. Almost immediately, the copepods, despite presenting a healthy appearance, stopped laying eggs. We checked the food, temperature, salinity, etc. However, we did not find any problem. Finally, one day, after turning it over a thousand times, it occurred to us that the only different thing was that screw. We installed a plastic one, and the copepods returned to lay eggs as usual. Consider that the water was only in contact with this piece for a few seconds, but it still affected them sublethally. Today, we know that copper inhibits vitellogenesis (egg yolk formation) in copepods and therefore negatively affects egg production.

Cop√®pod Paracartia grani from the permanent culture at the Institute of Marine Sciences, CSIC.

I witnessed another curious example during my postdoc at the University of Hawaii (USA). At that time, we carried out monthly oceanographic campaigns in Pacific waters, in which I had the privilege of participating. On those scientific cruises, we took seawater with Niskin bottles (plastic cylinders with caps at both ends) mounted in a rosette around a CTD (a device that measures conductivity, temperature, and depth). In two of those Niskin bottles, the O-ring, which ensures they close properly, and no water is lost, broke. As there were no more O-rings of the same high quality (they were free of trace metals), the technician in question replaced them with standard ones made of black rubber, which are common in plumbing. During the following cruises, in those two bottles, there was always a drop in primary production (algae production) measurements of approximately 20-30%. New, better-quality O-rings arrived, and the problem went away. Such an insignificant detail, because the rings are almost not in contact with the water, affected the algae negatively and forced us to throw away all the data corresponding to those samplings. Let me add that most Niskin bottles in use today still have the typical black plumbing O-rings. Because this was never published, it has not reached the scientific community. To publish it, it would be necessary to do more tests with different communities and more replicates. However, in the end, the problem is there.

Rosette of Niskin bottles mounted around a CTD

Many pollutants can affect plankton, some of them classic and well-known, such as hydrocarbons or heavy metals, and others emerging, which have seldom been taken into consideration, such as nanoparticles, hormones, medicines, plasticizers, etc. We know little about what effect they will have on plankton. Nor do we know if the increase in temperature will act synergistically with them to the detriment of plankton. We still have a lot to learn, but, in the meantime, I would ask you to take care of our precious and delicate sea and the creatures that live in it, including the plankton. I would also ask you to think that, although invisible, the planktonic food web makes up an ecosystem as complex and precious as an oak grove or a pine forest.

Our copepod cultures

Today I will present you our copepod cultures. Some of them have been decades with us.

Oithona davisae 10x objective
Paracartia grani 5x objective
Centropages typicus 10x objective

The nauplii of the three species are also different:

These are a nauplii of Oithona davisae. They are usually pointy towards the end and have two spines in the posterior part that are almost touching by the end.

Paracartia grani nauplii are more “rectangular-looking” and the spines are open towards the sides, never touching by the end.

In the case of Centropages typicus there are a long and a short two parallel spines in the posterior part.

Plankton and art

Those who have seen a plankton sample cannot deny its inherent beauty. From the perfect symmetry of diatoms to the complexity of some radiolarians, we can find an infinite range of shapes and colors that have been a source of inspiration for many artists, ancient and modern. Perhaps we find the maximum expression of the representation of plankton in painting. Particularly, toward the end of the 19th century and the beginning of the 20th, a series of artists exceptionally illustrated the plankton. Among these, I would undoubtedly highlight Erns Haeckel (1834-1919), who drew marine creatures, and in particular plankton, with a detail and beauty that had never seen before (Figure 1).

Figure 1. Drawing of Radiolaria by Erns Haeckel

If we talk about artists and plankton, I cannot fail to mention Miquel Alcaraz, my former advisor and friend, who recently disappeared, leaving us without a great scientist and painter of plankton (Figure 2).

Figure 2. Centropages typicus developmental stages painted by Miquel Alcaraz

Plankton have also inspired artistic creations, which are not purely descriptive. There is a long tradition of naturalists and researchers who devoted their time, around the 19th century, to create true masterpieces of art and monuments to patience, slowly placing under the microscope different species of diatoms in the correct position to create compositions that, often, remind church rose windows (Figure 3).

Figure 3. Compositions with diatoms. Left J.D. M√∂ller, right Eduard Thum

Many sculptors also find an endless source of inspiration in planktonic creatures. For example, Mara Haseltine’s glass figures represent tintinnids, radiolarians, and other plankton organisms in a very creative way. Louise Hibbert also represents plankton, among other creatures, in her sculptures. If we move from art to artistic merchandizing, it is not difficult to find pendants inspired in plankton, usually made with 3D printing and coated with more or less precious metals. I leave you in Figure 4 a collection of all these creations (without putting commercial names or sales websites, which would not be appropriate).

Figure 4. Different sculptures and works of art inspired by plankton. Above, glass works by Mara Haseltine; middle, sculptures by Louise Hibbert; below, commercial pendants.

Cinema is closely related to painting and sculpture and is another of the world-renowned arts. We already met the Phronima in a previous post (, which surely inspired the creature in the movie Alien, by Ridley Scott. However, it does not end there, from the misnamed character Plankton (it is actually a copepod) of SpongeBob animation to the short cartoon series Plankton Invasion, or the Golisopod from Pokemon (inspired by an isopod) we have representatives of plankton everywhere (Figure 5). Returning to the descriptive art, within the audiovisual medium, I would highlight the videos of Plankton Chronicles ( or those of the YouTube channel from our research group (

Figure 5. Plankton in cartoons.

The literary works on plankton are also extensive, and there is something to suit all tastes, more or less scientific. However, if we are talking purely about fictional literature, we should not be surprised that plankton has also inspired some other books. As an example, we could cite the book Medusa by Sergio Rossi, where some marine biologists want to prevent a voracious species of jellyfish from ending the world’s fisheries, or the Fifth day by Frank Schatzing, where lobsters full of toxic dinoflagellates explode in the faces of humans who wanted to eat them. Maybe a little far-fetched, don‚Äôt you think?

Although it sounds unbelievable, there are also architectural structures based on plankton. The diatom-house designed in Germany is an example. The Korean building that simulate the cycle of elements in the planktonic food web is another (Figure 6). There is also a team of architects called the Plankton Group; however, I do notsee much of a connection between this latter building and these creatures.

Figure 6. Left diatom house. Right building inspired by the cycle of the elements

I do not know much about the relationship between plankton and music or dance. Even so, there is a music group called Insect surfers, which released the song Plankton Dance in 2014. However, the truth is that it becomes difficult to find a relationship between that song and plankton.

Finally, even though it is not one of the seven arts yet, we cannot deny that knowing how to cook is quite an art. Well, there are a few dishes with plankton, and they are becoming fashionable as an haute cuisine ingredient. From the traditional Chinese marinated jellyfish to the sophistication of dishes with marine phytoplankton (freeze-dried algae cultures sold at exorbitant prices) promoted by the Spanish chef Angel Le√≥n, we have a variety of dishes using plankton as ingredients that we can enjoy. I had myself a Calanussoup at a meeting in Germany. I admit, however, it was rather tasteless. 

Plankton are also being used in the supplements, such as Omega 3, Spirulina, etc. 

In summary, either because we enjoy art, movies, or simply cooking with plankton, it is undeniable these creatures have entered into our lives.

Microplankton sample, 11/20/2022

I leave you with a selection of pictures from the last plankton sample (2 Km offshore Barcelona, 5 meters depth, November 20, 2022). You can find the movies here: for a summary of the relevant species for Acantharia for a beautiful Amoeba for Ceratium spp.

A¬†brief¬†history of plankton discovery

In this post, I will give you a few glimpses of how were the early plankton-human interactions and how we managed to study these creatures. As you will see, there was already evidence from ancient Greece that there were strange beings, including plankton organisms, that did not fit into any known classification. However,perhaps the greatest work was done by a series of amateur and professional naturalists from the 16th to the 19th centuries. Their discoveries were not always published as books but were often contained in correspondence they maintained with recognized institutions, such as the Royal Society of London. Even though many valuable records are certainly lost, a good part of this correspondence is still available, and we have evidence of the exciting progress of those people who had a whole new world to discover. You will see that I give special emphasis to the first illustrations of plankton because, as the popular saying dictates, many times a picture is worth a thousand words.

Multicellular plankton

Logically, the first recorded members of plankton were possibly jellyfish and other larger organisms, particularly those that lived attached to other animals for daily consumption, such as fish. Already in the 4th century BC, the great philosopher and naturalist Aristotle first identified a parasitic copepod. He classified it, like jellyfish and other soft-bodied organisms, such as sponges and ascidians, under the name Zoophyta, something between animals and plants, and that classification lasted for hundreds of years. However, we owe the first image of a parasitic copepod (Figure 1) to Gillaume Rondelet, a French zoologist born in 1507.

Figure 1. Below, on the right and above the tuna’s gills, you can see what could be a parasitic copepod. Illustration by Rondelet (1554).

The free-living copepods had to wait slightly longer to be discovered; in 1688, Stephan Blankaart drew the first recorded free-living (freshwater) copepod (Figure 2). Carl Linnaeus (father of modern taxonomy, 1707-1778) named them Monoculus and classified them as insects. As insects, they remained for many years until the beginning of the 19th century, when Jean-Baptiste Lamarck classified them as crustaceans, along with water fleas, amphipods and isopods.

Figure 2. The first illustration of a free-living copepod, left. Possibly of the genus Cyclops from a sample of freshwater. Stephan Blankaart (1688).

Out of curiosity, the first illustration of a free-living marine copepod corresponds to Gunnerus (1770), a Norwegian zoologist who identified Calanus finmarchicus (rather numerous and important species on the Norwegian coast), although he called it Monoculus finmarchicus (Figure 3).

Figure 3. The first illustration of a free-living marine copepod. Ernst Gunnerus (1770).

Unicellular plankton

We owe the discovery of protists to Antonie van Leeuwenhoek, who with his rudimentary microscope first saw infusoria and other planktonic organisms. Between 1674 and 1716, this Dutchman, recognized as the father of microbiology, described several species of protozoa, mostly ciliates (infusoria, Figure 4), among other planktonic creatures.

Figure 4. Drawings of different infusoria and other organisms made by Antonie van Leeuwenhoek 1702.

He did not pay much attention to planktonic algae, and although he surely saw them, the first diatom (not quite planktonic) was described by an English gentleman, probably Charles King, in 1703 in a note sent to the Royal Society of London. From here, many naturalists devoted themselves to classifying, observing, and drawing protozoa (for example O.F. M√ľller has a detailed description with drawings of the behavior of tintinnids dating from 1779. Of course, the maximum expression of art depicting these beautiful creatures can be found in the drawings of the German Ernst Haeckel (Figure 5). This artist and scientist suggested in 1866 that all those animals (including bacteria) that he saw under the microscope should constitute by themselves a third independent animal kingdom called Protista (the first or primordial).

Figure 5. Illustrations of different protozoa by Ernst Haeckel.

Plankton research

Many years passed from the discovery and classification of planktonic organisms to the beginning of research into their role in the oceans. The first studies, purely descriptive of the diversity of life forms, were linked to large expeditions, such as those of Captain James C. Cook between 1768 and 1780 in the Pacific Ocean. In those expeditions, there is evidence, for example, of spots of the cyanobacterium Trychodesmium on the surface of the ocean. However, the first nets specifically designed to collect plankton were probably used by the French naturalists Francois P√©ron and Charles-Alexandre Lesueur during an expedition to Australia from 1801 to 1804. Additionally, during the long voyage of the HMS Beagle (1831- 1836), Charles Darwin used nets to collect samples of plankton. However, we own the creation of modern oceanography to the Challenger expedition (1872 to 1876), as it was the first organized specifically to collect data from the marine environment, including temperature, water chemistry, bottom geology, currents, and marine life. The HMS Challenger was equipped with laboratories and microscopes, as well as a team of six scientists.

In 1887, the physiologist Victor Hensen introduced the term plankton to describe all those animals that drifted in water currents. He was also the first to propose that perhaps marine life was not nourished by what flowed into rivers but by microscopic primary producers. Through his studies, he perfected existing plankton net designs and created one that was truly quantitative and is still used today (the Hensen net). From the analysis of his samples, he came to the erroneous conclusion that plankton are homogeneously distributed in the ocean and that there are too few of them to sustain fisheries. Facts that were refuted immediately afterward. The study of the distribution and abundance of the different plankton groups continued during the late 19th and early 20th centuries with names such as Marie Lebour (specialist in diatoms and dinoflagellates, 1876-1971), Alister Hardy (creator of the continuous plankton capture system, CPR, 1896-1985), Sheina Marshall (a pioneer in the study of copepod feeding, particularly Calanus sp. (Figure 6), 1896-1977), Hans Uterm√∂hl (inventor of the sedimentation chambers named after him, 1896-1984), to name a few of them. The result of those studies is the discovery of daily patterns of vertical migration, for example. In 1817, the French naturalist George Cuvier made observations of the vertical migration of zooplankton, although he did so in a lake, and his study lasted only one day. More complete, marine and long-lasting were the investigations of the German Carl Chun, in 1888, on vertical migration.

Figure 6. The marine copepod Calanus hyperboreus.

Although there were hints of their behavior, what those microscopic beasts actually did in the sea was still mostly a mystery, and we had to wait until the 20th century for estimates of, for example, primary production, first with variations in oxygen measurements under light and dark conditions, and afterward using radioactive carbon. Similarly, the estimation of zooplankton production was established as a technique well into the 20th century. In 1963, Ramon Margalef established the basis for understanding the structure of the ecosystem and the relevance of ecosystem maturity in species succession. By the end of the 20th century, MR Landry and RP Hassett devised a method to estimate the impact of microzooplankton feeding on phytoplankton in seas and oceans. At approximately the same time, F Azam, T Fenchel and other collaborators conceptualized the operation of the microbial network and introduced the term microbial loop, which takes into account the tremendous importance of dissolved organic compounds and the key role of bacteria in the marine food web. All these milestones have been decisive in positioning us into current knowledge. However, although we have come a long way and have modern techniques and disciplines at our fingertips, such as satellite imaging, sequencing, genomics, and gene expression, we are still in the infancy of fully understanding (and predicting) the function of the different plankton groups in the marine food web.

Marine Zooplankton Ecology Group Youtube Channel

In the following link, you will find our Zooplankton Ecology Group Youtube Channel. It has many videos of the different organisms we found in our samples, including metazoans and protozoans. You also will find a video on how to make your home-made plankton net. I leave you a few links to the newest and the most popular ones. I hope you enjoy it.

The ciliate that met a diatom: a case of symbiosis in plankton 

Sometimes, very different organisms get together and form a successful consortium. Lichens, for instance are a symbiotic consortium between and algae and a fungus. In the plankton we have similar relationships. For instance, a ciliate and an alga, once in a while stop being grazer and prey and work together for a better success. This is the case of the ciliate Eutintinnus sp. and the diatom Chaetoceros (usually Chaetoceros tetrastichon or C. dadayi). The ciliate gets protected by the long spines of the Chaetoceros and this, at its turn, gets to travel for free. It is very rare to find both species alone.

The marine food web

Here you have a marine food web graphic representation using some of my drawings. Feel free to use it for teaching, although I would ask to mention the source and authorship.

The little blurry dots represent virus and bacteria. Given they feed at all levels of the food web I positioned them all around. I hope you like it. Phytoplankton are at the base of the food web, together with some small mixotrophs. Both are grazed by larger heterotrophic and mixotrophic protists, such as ciliates and dinoflagellates, but also by appendicularians. Copepods are one step above; although they graze on both large and small protists I kept them on an upper position on the food web. Above them, we have krill, whales and jellyfish. On top of that we have fish, and at the highest level of the food web we found sharks, although humans would be a perhaps more realistic end point for the food web.