Year Of Plankton

This year we have launched a Year Of Plankton, an initiative to share interesting plankton facts and photos to help build your plankton knowhow! On this page you will be able to find the latest entry for the week, as well as all entries from previous weeks, in case you missed out.


Paracalanus are small (0.5-1.4 mm) copepods, very abundant in coastal environment but also found in open ocean.

Two key features help when trying to identify Paracalanus; a) unlike most other small copepods, the swimming blades at the end of their swimming legs are smooth, not serrated, and b) the pouch where females store the male’s sperm (called a seminal receptacle) is long and narrow, like a letter box.


Species belonging to the genus Pseudocalanus are among the most abundant small copepods in North Atlantic waters.

These coastal species are generally found in the upper layers of the sea, and despite their small size (1.7mm), are an important prey for many larger zooplankton and larval fish.

Temora stylifera 

Temora stylifera is a coastal copepod and is one of the most abundant species found in the waters off Brazil.

It is also found off Mediterranean coastal waters.

The Temora family of copepods are quite easy to identify compared to other copepods due to their long caudal rami (tail end) and somewhat coffin shaped body.


They create feeding currents by beating their appendages (antennae and maxillipeds); this helps with propulsion in the water and they can search for food by hovering in the water column.

Acartia clausi 

Acartia clausi is a hairy looking, common coastal copepod.

This marine creature has long hairs on its antennae, at the end of its legs and the end of its urosome (tail).

To help identify it, A. clausi has characteristic spines on the end of its metasome (body) that look like a row of teeth.


During times of adverse environmental conditions, this species can produce resting eggs as a survival strategy.

These are different to normal eggs as they are able to temporarily pause development until conditions improve.


Great to see phytoplankton feature on Blue Planet II last night!

But what causes phytoplankton to bloom? Phytoplankton cells absorb the necessary substances for growth and reproduction directly from the surrounding water.

However, for a bloom to occur, environmental factors such as salinity and water temperature must be just right, and essential nutrients, like nitrogen and phosphorus, must also be present in the right amount.


Each species of phytoplankton has its own set of favourable conditions, and so blooms are usually of one or two species.

Most blooms are temporary events that will disappear when the nutrients have been used up or wider conditions are no longer favourable.


We loved the jellies on last night’s Blue Planet 2!

Did you know a collective noun for jellyfish is a smack?!


Most jellies primarily feed on plankton, although larger jellies also eat crustaceans, fish and even other jellyfish.

During favourable conditions, plankton populations bloom which provides jellyfish with a plentiful food supply enabling them to reproduce rapidly.

At SAHFOS we regularly record the stinging cells (called nematocysts) from jellyfish on our CPR silks!

Pleuromamma xiphias 

The copepod Pleuromamma xiphias is easily recognised by a sharp point on the top of its head.

It is thought to be named after another creature with a sharp pointed head, the Swordfish, whose Latin name is Xiphias gladius. P. xiphias is a cosmopolitan copepod that uses bioluminescence to avoid being eaten by predators.


Unlike most copepods which produce flashes of light internally, P. xiphias releases its bioluminescence chemicals from luminous glands on its swimming legs; this glow then hangs in the water and distracts predators while the copepod escapes.

Odontella sinensis 

The marine diatom Odentella sinensis looks like jewels under the microscope but is a type of algae, and one of the most common types of phytoplankton.

These diatoms have cell walls made of silica, which makes them hard and shimmery, but they also contain chloroplasts for photosynthesis, like plants on land.


Odontella sinensis used to occur solely in Indo-Pacific regions, but at the beginning of the 20th century made its way to Europe and rapidly spread throughout European waters.

It is highly likely that this invasion happened via ships ballast water.

Odontella sinensis are also known as Chinese diatoms, as they were first described in the China Sea in 1866.


We loved the #plankton ballet on the BBC’s #BluePlanet2 last night! The leaping mobula rays were feasting on small shrimp-like crustaceans known as euphausiids, like this one. These organisms have small complex light organs called photophores in their thorax and abdomen, which bioluminesce, causing the bright flashes  of light. The name Euphausiid actually comes from the Greek Eu- for good or true, and –phausia, which means shining or light emitting #yearofplankton


Candacia armata

Candacia are robust and powerful copepods. With a distinct flat head and square shoulders, they are carnivorous – grasping prey like appendicularians and chaetognaths with very strong and developed mouthparts. They can have distinct black or brown pigments on their swimming limbs, which can remain even after preservation and characteristic asymmetric swellings on a segment of the body used in copulation, known as the  genital somite. Typically  found in oceanic regions, C. armata are associated with influxes of oceanic water, and are found regularly by SAHFOS analysts in samples from the North Sea and English Channel.



Siphonophores are amazing! Belonging to the same group as jellyfish they form colonies composed of many individual organisms (zooids), but the integration of the individuals is so strong that the colony functions like a complete organism in itself. In fact, most of the individuals are so specialised (e.g. they keep the colony buoyant, emit light to attract prey, possess stinging cells to capture prey) that they are unable to survive independently. Because they operate like more complex organisms, siphonophores may provide clues regarding the evolution of more complex bodies.

Ernst Haeckel described a number of siphonophores, and several of the most beautiful plates from his Kunstformen der Natur (1904) are devoted to them.


One of the species of siphonophora you may be familiar with is Physalia physalis, the Portuguese Man o’ War, also known as the floating terror! It can deliver a painful sting and is sometimes found washed up on the shore, particularly after strong onshore winds.



These Evadne (commonly known as water fleas) are able to switch their reproductive strategy depending on their surrounding environmental conditions.

In times of plenty, Evadne produce live young asexually, which you can see developing inside the adult. Sometimes, you can see a “Russian doll” effect, where young develop within young.


In stressful environments, Evadne switch to a sexual phase, producing eggs that are encased in hard protective shells.

These eggs can withstand less favourable conditions, increasing the chances of hatching in better environmental conditions and surviving.


Chaetognaths are more commonly known as arrow worms.  As their name suggests, they have a streamlined torpedo shaped body, terminating in a horizontal tail fin, which helps them move rapidly through the water.

Chaetognaths mainly tend to stay on the sea floor during the day but swim to the surface at night, perhaps to avoid predation from fish, whales and molluscs.

They have a very successful feeding mechanism; tiny cilia (hairs) found on their head detect vibrations of nearby copepods, other zooplankton and even their own kind, sharp hooks and teeth on their head grab their prey, holding it while they release a deadly neurotoxin to paralyse their prey, allowing them to swallow their prey whole.

Research has found that Chaetognaths have a group of bacteria that live in them called Vibrio that actually produce the active substance in the toxin.

Metridia longa

There may be no sunshine in the ocean at night or at depth but it is not without light. Many sea organisms have the ability to create their own light sources through bioluminescence. The copepod Metridia longa has been found down to depths of 100m emitting its own light source. Similar to fireflies they use the enzyme luciferase to produce their light. This enzyme is also found in a variety of other organisms such as jellyfish, dinoflagellates, sea pansies and even mushrooms!


Paralia sulcata

Paralia sulcata is a robust chain forming diatom and is thought of as a benthic species (an organism that lives near or on the ocean floor).

However, during winter months storm-induced mixing in the water column brings these common cells up into the plankton.

The term tychoplankton is given to organism, such as Paralia, that get washed up into the plankton.

Interestingly, P.sulcatais just as common in our coastal waters now as it was millions of years ago and scientists have found that it is sensitive to changes in water conditions.

Used as a paelo-indicator, the abundance and cell size of Paralia micro-fossils can reveal to us how our ancient oceans once worked.


Bacillaria are pennate diatoms that move in an extraordinary fashion.

Most phytoplankton depend on flagella or cilia to propel themselves through the water, however, Bacillaria cells “swim” with no obvious apparatus.

Looking down the microscope, entire colonies of Bacillaria line up and then slide apart, going back and forth over one another repeatedly, allowing the shape of the colony to change from a long line to a square box very quickly.

The cells fit together with a form of ‘tongue-and-groove’ along the side of the cell, called the raphe.

Despite being one of the first diatoms to be described, it is still not known for certain how exactly these cells move; Bacillaria may have solved their lubrication problems with techniques yet unknown to engineers.

Labidocera aestiva 

Labidocera aestiva are neuston copepods – this means they occur in the upper few millimetres of the water column.

Their large size (1.75-3.00mm) and often colourful appearance makes them an attractive meal to passing fish, so they must have an effective escape mechanism to avoid being eaten.

Many copepods can perform powerful escape jumps enabling them to dart away from the jaws of predators, but L. aestiva takes it to a whole new level.

Researchers using high speed cameras recorded individuals leaping out of the water and travelling many times their own body length to avoid predators!


Despite losing up to 88% of their initial kinetic energy, the researchers found that copepods that break the water surface travel significantly further than those escaping underwater, and successfully exit the perceptive field of the predator – resulting in a highly effective defence mechanism against sub-surface feeding visual predators.

Nannocalanus minor

Did you see the #eclipse in the US last week? Total solar eclipses have been found to cause changes in some animals behaviour:

A total solar eclipse occurred on Saturday, March 7, 1970, visible across most of North America and Central America.  Totality was visible across the Gulf of Mexico, where scientists from the Departments of Oceanography and Meteorology from Texas A&M University had travelled aboard the research vessel Alaminos to study any potential effect the eclipse may have on the zooplankton in the region.

Most marine zooplankton exhibit some pattern of diel vertical migration, usually one of ascent at night and descent during the day. Nannocalanus minor has a small diel vertical migratory range of this nature.

N. minor was caught frequently at a depth of 25m the day before the eclipse, and were abundant at the surface that night. They disappeared from the surface during the morning before the eclipse, but appear to have undergone a dramatic change in vertical migration during totality, being captured almost exclusively at the surface, and in greater number than any other species. Shortly after the eclipse ended, N. minor were captured again at 25m, and soon appeared to have resumed their customary daytime distribution. 


Calanoides carinatus 

Calanoides carinatus is a copepod that dominates the plankton in upwelling systems.

These are areas of ocean where winds blowing across the surface push water away, allowing cooler, deeper water to rise to the surface.

These deeper waters are typically rich in nutrients and act as a natural fertiliser to the plankton in the surface water, resulting in areas of high biological productivity.

In equatorial African waters, C. carinatus has been found to be so strongly associated with upwelling that they only appear in surface waters during upwelling events.


At the end of the upwelling season, juveniles in some populations of C. carinatus suspend their development and migrate to a depth of 500m for up to 9 months, until upwelling resumes. 

Ceratium hexacanthum 

Plankton in the post! Ceratium haxacanthum is a marine dinoflagellate commonly found in North Atlantic waters.

Its distinctive reticulated cellulose armour and convoluted horn make it easy to identify amongst its fellows in the group Ceratium.


Like many species of Ceratium, C. hexacanthum often forms chains of several individuals, you can see one in this video dancing around thanks to its whirling flagella


Some phytoplankton appear so similar it can be difficult to identify which species they belong to, so they are grouped together in a “species complex”.

Pseudo-nitzschia has two complexes, Pseudo-nitzschia seriata complex and Pseudo-nitzschia delicatissima complex.


New technologies which use genetic material (known as molecular probes) have made it easier for quick determination of species; knowing which species occur where is important as Pseudo-nitzschia species are one of the main producers of the neurotoxin domoic acid, the chemical responsible for causing amnesic shellfish poisoning.


Coccolithophores are very small single celled phytoplankton (algae) that often have very intricate, chalky plates on their surface, known as liths.

Despite their size (0.1mm max) coccolithophore liths can reflect sunlight, allowing them to be seen from space by satellites.


These organisms can occur in huge numbers, in fact, the white cliffs of Dover are almost entirely composed of the liths of prehistoric coccolithophores!

Centropages typicus 

This copepod’s eyes are bigger than its stomach!


Centropages typicus are omnivorous, regularly feeding on small algae and microzooplankton, but they have been reported eating newly hatched fish larvae that are bigger than themselves!

Fish eggs, however, appear more difficult to grasp and eat, even if they’re smaller than the fish larvae.


C. typicus use a mixture of mechano- (movement) and chemo-receptors (chemical) to locate their prey; once they have detected a prey item, individuals can capture it in less than 14 milliseconds!

Clues to aid species identification

The shape and size of the final pair of swimming legs in male copepods often provide helpful clues when trying to identify which species they are. In females this pair of legs, called p5s, look very similar to the rest of their legs, or can be reduced or even absent in some species. In contrast, male p5s are often species specific, appearing asymmetrical and highly modified.

This pair of limbs is important during reproduction, helping to capture females and transfer spermatophores (little sacs of sperm) from male to female. The shape of p5s can vary from rounded claw-like limbs to much bigger complex looking limbs. #yearofplankton



From the Latin meaning ‘hole bearers’, these Foraminifera are protists – organisms that are neither plant, animal or fungi.

Most species produce a hard outer shell, known as a ‘test’, which can form one or many chambers, with some appearing very ornate.

The majority of marine foraminifera are benthic (living in or on the sea floor) but a small number are planktonic, drifting along in the sunlit surface layers of the ocean.


Foraminifera tests are resistant to decay, and so are often found fossilised in the sediment.


This information can be used by oil and gas companies to help reconstruct past climates and ocean currents when they’re looking for new hydrocarbon deposits.


Mysids: these crustaceans are commonly called opossum shrimp as females carry their developing young in a bulging pouch, or marsupium, at the base of their legs.


The size of the brood is proportional to the body length of the female and food availability, with females able to carry up to 30 fry in the pouches, although 6-7 is more typical.

Mysids are omnivores, feeding on algae, detritus and other zooplankton, but they also have cannibalistic tendencies, often preying on their own young once they emerge from the marsupium.

95% of the world’s mysids are marine and can be found in deep open ocean through to shallow coastal waters.


Males of the copepod genus Sapphirina shimmer when sunlight bounces off their crystalline exoskeleton, earning them their common name of Sea Sapphire.


Their characteristic spiral swimming behaviour accentuates their colours, with flashes of blue, violet, red and yellow at every twist and turn. In contrast, females are almost transparent in colour, have large eyes and parasitise large gelatinous creatures called salps; individuals enter the salp using hooks on their antennae and feed on the internal body tissue.

Males however are too large to fit inside salps, and as they have a reduced gut, scientists believe some do not feed at all during their adult stage.


Algae, like these Coscinodiscus, are some of nature’s most effective solar powered organisms. Their glass-like cell walls are made from silica, and are covered in pores arranged in complex symmetrical patterns, allowing light to flow into the organism without letting any escape.

In European waters, the non-native diatom, Coscinodiscus wailesii, can occur in huge numbers, often forming up to 90% of the total algal biomass. However, due to its large size, it is inedible to most zooplankton. This bloom-forming species was first recorded in the CPR Survey in 1977, thought to have been introduced by either ballast water or through oyster imports. It is important to monitor this species as in large numbers, it produces copious amounts of mucilage (slime) which can blanket the seabed, threatening benthic species.

Photo credit: thanks to Robert Lavigne from for permission to share both images


This mass of cells is actually a colony of Zoothamnium, a genus of marine ciliate.

Each cell is connected to a central stalk containing a contracting band, which allows the whole colony to contract and move in unison.


These colonies often attach themselves to planktonic crustaceans and can sometimes be so dense, they affect the swimming and feeding ability of the host.

When the host dies, the individual cells can dissolve from the colony and float freely, for up to 12 hours, allowing them to drift to a more favourable location or a new host.


Lucicutia, the shining stars of deep-sea plankton appear to glow in the water.

These copepods, first identified by taxonomists Giesbrecht and Schmeil in 1898, were named Lucicutia, which comes from the Latin LUX (meaning light) and CUTIS (meaning skin).

Today we know that it is not the skin of these animals that glows, but that glands on their bodies secrete bioluminescent material into the surrounding waters.

Although the majority of Lucicutia species spend most of their time in deep water (200m),  we often spot 1 or 2 species on our CPR silks from samples collected at night.


The copepod genus Caligus, commonly known as fish lice, parasitise a wide range of farmed and wild fish species. 

Their vampiric and flesh eating feeding behaviour can have a serious effect on the host, compromising immunity, with severe infestations often proving fatal. 

So called ‘epidemics’ of fish lice have been seen to drive up the price of farmed salmon and there is growing concern that global warming may further fuel plagues of these parasites, as warmer waters allow them to breed in larger numbers.


Phronima are small amphipods (crustaceans) found in the deep sea, though they come to the surface to feed at night.

They bear a startling resemblance to the Alien queen from the movies, and this terrifying appearance (albeit on a miniature scale!) doesn’t stop just at the looks.


Phronima like nothing better than feeding on the insides of barrel-like salps (animals similar to jellyfish), and then using the gelatinous body of the host as a mini-submarine, as transport and a nursery for their developing eggs!

Echinoderm larvae

Starfish, sea urchins and sea cucumbers all belong to the taxonomic group (phylum) Echinodermata, and are exclusively marine.

During spring and summer months, adults release eggs and sperm straight into the water.


Fertilised eggs then develop into the first of many larval stages, which depending on the species, last between a few days to several weeks, before they develop into an adult form.

As in many marine animals, the planktonic larval form bears little resemblance to the adults’ form, with some looking more like human ears or spaceships than starfish!


Asterionellopsis glacialis

The phytoplankton (algae) Asterionellopsis glacialis, thrives in turbulent waters and is often referred to as a ‘surf diatom’.


Despite being cosmopolitan in distribution, this species often accumulates in high numbers in the surf zone (where waves break), appearing to favour this extreme environment.

Due to proximity to coastal areas, surf diatoms are particularly sensitive to changes in surf zone dynamics, for example, sediment deposition caused by dredging or increased rainfall.

Penilia avirostris

Penilia avirostris is one of the few truly marine species of the order Cladocera, commonly known as water-fleas.

This species is not native to UK waters, with theories of its introduction including both warming sea surface temperatures and an increase in anthropogenic activities (through ballast water transport).


Over the last two decades, this species has expanded its range further north and is now an important component of the summer plankton community in the North Sea.

Dinophysis norvegica

They may be microscopic but these phytoplankton have the potential to make you ill.

Dinophysis norvegica is a bloom-forming toxic species associated with Diarrhetic Shellfish Poisoning (DSP) events around the world.

 These organisms can bioaccumulate (build-up) in shellfish, which when eaten by humans, can cause sickness. These DSP events can cause shellfish farms to close temporarily, causing a significant loss in revenue – by monitoring the distribution and abundance of species like these, suitable management action can be taken to prevent this happening.

Fish larvae

Did you know fish begin life as eggs and larvae in the plankton, drifting with the ocean’s currents?

When larval fish first hatch, their mouths and gills are not fully developed; young must rely on an internal yolk sac for food and absorb oxygen through their developing fins for the first few days of their life.

Once they are able to feed, species like these cod initially feed on copepod nauplii (juveniles) before actively seeking larger copepods, like Calanus finmarchicus (pictured here).


These brightly coloured copepods have a surprisingly dark feeding habit.

Using sensory organs (as they lack an image forming eye) members of the genus Oncaea locate large zooplankton, like arrow worms, in the water around them, and latch on using their antennae and maxillipeds (specialised feeding limbs).

They begin by grazing on food particles stuck to the outside of the host’s body, before piercing the host’s body wall and feeding on the body fluids inside!

Spring bloom

Did you know the oceans experience spring too?

During winter, rough seas increase mixing of the water column, re-suspending nutrients and phytoplankton cysts (resting stages of phytoplankton).

As spring arrives, with longer days and increasing light and temperature levels, diatoms like these are able to reproduce rapidly, leading to an event known as the spring bloom.


Although these organisms are microscopic, spring blooms can often be seen from space!

Tripos arcticus

Tripos arcticus is a cold water phytoplankton species from the Genus Tripos.

This species can bloom in very high numbers during winter months as they not only photosynthesise, like a plant, but also ingest smaller organisms too, like an animal.

During these blooms, T. arcticus can reproduce so rapidly the colour of the water can change to a reddish/brown colour, and in extreme cases, oxygen levels can become depleted, an event known as a Harmful Algal Bloom.

Calanus hyperboreus

Meet the deep water copepod, Calanus hyperboreus, an animal which dominates the Arctic Ocean in number.


It grazes on algae growing on the underside of the sea ice and on free-floating phytoplankton, and is sometimes referred to as the “little cow of the ocean”.

These food sources are important to help it maintain a high fat content, to help sustain it through the long dark winters.

In the Arctic, fats are the currency of life, and these copepods form the primary food source for many larger marine species, including Arctic cod.

Branchiostoma lanceolatum

These fish-like animals are called Lancelets and the closest living relatives of all vertebrates

Their body is supported by a primitive back-bone called a notochord, which prevents their bodies collapsing as they swim.

Scientists have been studying these animals as it’s believed they hold many clues to the evolution and development of all living vertebrates!

The most well-known representative from this group is the Branchiostoma lanceolatum, as seen in these pictures.


Pterosperma are recorded in the CPR Survey in their non-mobile cyst, or phycoma, stage, and look very similar to little flying saucers when viewed from above. They can be identified by their dense, inner structure, which can have single or multiple 'wings' or ala, often in circumference around the body.

Despite the species being poorly studied, it has been routinely recorded in the CPR Survey over the last few years and has an oceanic distribution in the North Atlantic, recorded throughout the year often during periods of high phytoplankton biomass (blooms).

Neodenticula seminae

The distinctive domino-like, chain-forming diatom Neodenticula seminae is considered the first plankton species to have made the crossing from the Pacific to the Atlantic Ocean via the increasingly ice-free Arctic. This species was last found in sediment records in the Atlantic from approx. 800,000 years ago. 

However, with the ice barrier reduced, a large volume of Pacific water first entered the Northwest Atlantic in summer 1998, carrying with it this diatom (there had been no shipping via this route, so ballast water transport has been dismissed). Since then the species has re-established itself across the northern North Atlantic.

Decapod megalopa

The crab equivalent of human teenage years is know as decapod megalopa! This name comes from the Latin meaning '10-footed' (Dec=10, pod=foot) referring to the 10 limbs all crabs have, and its stage 'megalopa' mega=big and lop=eyes, referring to the physical changes the crab goes through as it develops.


This megalopa stage is the final stage that occurs in the plankton, before the animal settles on to the sea floor and transforms into what we recognise as a crab.

 Decapod zoea

Once thought to be separate species, we now know that zoea are juvenile stages of crabs, lobsters, crayfish, prawns + shrimp.


 Antonie van Leeuwenhoek, “The Father of Microbiology” was, in 1699, the first person to describe the differences between the larval stages of crustaceans and their adult forms. Despite this, controversy remained about whether or not metamorphosis occurred in crustaceans due to observations based on different species, some of which do not metamorphosise. This controversy persisted until the 1840s and it was not until the 1870s that the first complete series of descriptions of crustacean larval forms were published.

Miracia spp.

Juveniles of the brilliant blue copepod Miracia spp. have to cling for life on ‘rafts’ of blue green algae, namely the filamentous cyanobacteria Trichodesmium. In the open ocean suitable substrates for the development of Miracia spp. are scarce, and Trichodesmium provides both a source of food as well as being a floatation aid to kickstart their development.


Noctiluca scintillans

When disturbed, these marine dinoflagellates (Noctiluca scintillans) glow, or bioluminesce – it’s easy to see why their common name is Sea Sparkle!

Unlike most dinoflagellates, N. scintillans do not feed via photosynthesis, instead they use their feeding tentacle to capture passing food such as diatoms and copepods! Check out their tentacles searching for food in this video clip! 



Did you know that before gluing themselves to rocks, juvenile barnacles begin life drifting in the plankton?

The early stage's of a barnacle's life include 2 free swimming stages, a nauplius and cypris stage, before they develop into adults and attach themselves to rocks.

Cirripede cypris  Cirripede nauplii      

Adult barnacles feed by pushing their feet through their 'trapdoor' roofs and waving them around to catch passing food! The last photo is of a barnacle exuvium - a complete exoskeleton an adult barnacle has shed in a moult - can you see the basket-like feeding limbs?

 Barnacle exuvium

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