Posidonia oceanica

Herbarium of Posidonia oceanica are the major Mediterranean ecosystem and play an important role in protecting against coastal erosion. It is in these herbarium that many organisms, animals and plants, find protection and food.

Geographic repartition
Posidonia oceanica  is an endemic species from the Mediterranean sea. It covers about 30% of the sea floor between 0 and 50 meters.

Life history traits
> Posidonia oceanica  has an terrestrial ancestor (returned to the sea there 100 Ma)  which it inherited flowers, fruits and roots. Flowering takes place in automn but not each year,  in an imprevisible way to avoid predators expecting the tasty fruits : sea olives.
P oceanica can reproduce in several ways : It can make sexual reproduction by selfing. The hermaphrodite flowers are fertilized by pollination hydrophilic. They lead to the growth of fruits that are marture in mai. When they are, they detached from the plant and float at the surface drifting with winds and currents. This way of reproduction allows Posidonia oceanica to colonize new regions and provides genetic diversity. This plant can also reproduce by cuttings and it has been observed that they can make pseudo-viviparity.

>The plants are organized in rhizomes and beams that can be orthotropic (perpendicular to the sea floor) or plagiotropic (parallel to the sea floor).

>  Posidonia oceanica fears freshening. Accordingly they are asbents from estuaries and outputs of groundwater zones. The optimal temperature for photosynthesis is 24°C and lethal temperatures are 10°C and 30°C.

Matte edification
Through the height growth of rhizomes in response to sediment deposition (trapped by the canopy), Posidonia built over the centuries a land called matte, formed by interlacing rhizomes and roots compacted by sediments. The matte can be several meters thick at a rate of one meter per century. This matte and leaves caused a diminution of currents in the herbarium. 

Herbarium types
Herbarium of plain : the most common  in the North Western Mediterranean Sea.
Herbarium of hill : where the depth is medium and the hydrodynamic strong.
Herbarium tabby : where the depth is low and is the warmer areas. Bands move parallel to themselves against the mainstream.
Herbarium in scales :  the walk back slope against the discharge current dominant.

Participating organisms and succession
Herbarium have a specific diversity very high : 20 to 25% of species of Mediterranean Sea live within it or can live within it. Herbarium are therefore a center of biodiversity.Over 50 characteristic species among which teleosts, molluscs, bryozoans, annelids, cnidarians, hydroids, echinoderms and rhodobiontes chromobiontes. Examples (from left to right) : Hippocampus guttulatus, Parastephanauge paxi, Asterina panceri and Opeatogenys gracilis.


A succession means a progressive series. For a herbarium of P. oceanica snaps into place, it is necessary that the following events take place :
After a few hours a bacterial film is deposited on the substrate. A few days/weeks after a turf of chromobiontes takes place. A few months/years after, chromobiontes Padina pavonica and Halopteris scoparia and the rhodobionte Jania rubens start to grow on the substrate. A few years/decades after rhodobionte Litophyllum and chromobionte Cystoseira also grow on the substrate. After a few decades if a cutting of P. oceanica is deposited on the substrate by the currents it will develop, grow and give birth to a herbarium with matte, 100 years after the filing of the biofilm.

This ecosystem is fragile and easily damaged by dredging and inks boats. it is important to preserve as best as possible.


Very instructive a pleasant to read, I recommend this book to everyone who wants to learnt about history while having the impression to read an adventure novel.

Why not the next book on your nightstand ?

Clownfish, a funny sex determination.

10% of fishes are successive hermaphrodites which means that they are male or female for a time and then they switch sex. Clownfish, its latin name Amphiprion is a case of successive hermaphrodism where sex determination is made by social factors.

Each family is organized auround an anemone with which they have a mutual relationship, and is composed by one dominant female, one reproductive male, and juveniles (immature et sub-adult males). There is no link between the size and age of individuals : small subadults are not necessarily young, the social structure of clownfish have an impact on the size of individuals. For cons, the female is always the oldest of group. The female has an aggressive behavior to juveniles ; there sperm production is inhibited by hormonal and behavioral factors : submission. When the female died the inhibition is lifted, the reproductive male becomes the female in 4 weeks (oestradiol rate increase) and one sub-adults become the reproductive male. This is a case of protandry : the species is firstly male and then female, to improve reproductive success.


When the reproductive time is come the male adopts a behavior signal jumping, fast swimming up and down to attract the female. It also becomes more aggressive towards his partner and shows off in front of her still or on the side, all fins deployed. The male chooses a nest site on a bare rock near the anemone. Sometimes he chews the tentacles of the anemone so they retract and thus frees up spawning in the disk of anémone. Anemones sandy bottoms do not offer surface conducive to spawning. The fish can solves this problem by bringing a suitable surface on its territory such as tests of echinoderms, bivalve shells, pieces of palm leaf or cans. This support nesting can thus be moved several meters until its anemone. Then the female swims slowly rubbing her abdomen on the rock, laying eggs, closely followed by the male fertilizes the eggs as and mesure. The nest can count from 600 to 1600 eggs.


Just before hatching, the embryo with its large shimmering pupils is visible through the transparent membrane. We also distinguish the red-orange yolk that gives the overall color of the eggs. Eggs hatch only at night, after 7 to 10 days. After hatching, the larvae spread in the plankton living in the ocean surface passively carried by currents. The larvae are transparent and are about 3-4 mm. The last larval period of 8 to 12 days and is one of the shortest among this fish family, which certainly explains the low range of species. The larval stage ends when the larvae reached the bottom. This initiates the metamorphosis into juvenile acquires its new colors. This transformation occurs in about one day. It is therefore vital for them to find a sea anemone to join, otherwise it will probably be eaten by a predator. Some species locate cnidarians following a chemical marker while others spot them on sight or by chance.

Clownfish are not directly threatened, but through the destruction of their habitat by global warming and human activities.

Catch them all !

You were sure to have them all caught? Get out your Pokeball, there is a new one !
Actually, this is not really a pokemon. It is Glaucus Atlanticus, a mollusk 3 to 6 cm long that belongs to the nudibranchs family.

This beautiful beast lives in tropical and temperate water, where it floats belly side on the top among neuston; organisms living floating at the air-water limit. Its floatability is due to an air bubble contained in its stomac. Despite its littleness, Glaucus atlanticus is a predator of hydrozoans like Physalia physalis or Velella velella. It consumes them using its chitinous jaws. This hydrozoans contains in their tissues nematocysts that are capsules containing venom inside cnidocysts. They are preserved by Glaucus Atlanticus in his own tissues, conferring to the nudibranch an urticant power.

Lateral expansions that you can observed are epidermic appendages called cerata. Within Glaucus atlanticus cerata are generally distributed on 6 appendices, and it can gets rid of them by atotomy through the sphincters present at the base of these. These cerata play a role in respiration through O2 duffusion through the skin to the blood. They are also protection appendages containing the cnidocysts.
The head is small and indistinct, provided with a pair of oral tentacles and a pair of very small conical rhinophores on the dorsal side. Rhinophores are sensory antennae that are characteristics of nudibranchs. They detect the noise, odor and allow taste.

A similar specie is Glaucus Marginatus. It is smaller ; 12 mm long and sports a higher number of cerata distributed on 8 appendices.  It appears on the image below eating an hydrozoan.
Both of Glaucus antlanticus and marginatus are hermaphrodite; each individual owns both male and female organs but cannot self-fertilize. Fecondation is internal, and a string of eggs is laid floating at the surface. They will develop in a trochophore larvae and then in a veliger larvae  which will leave the string to live a free life and develop in an adult nudibranch.


These nudibranchs are a « textbook case » of bidirectional homochromy. The underside of their bodies and cerata, which corresponds to the upper side, is blue or blue and white, which allows it to be camouflaged against aerial predators like birds. The dorsal surface, which corresponds to the underside, is silvery gray which is an effective camouflage against predators marine like fishes.

As we can see, there is no need to delve into science fiction movies like « Avatar » to see a surprising and wonderful nature. To make it continue, we have to protect it.

A new hope for breeding fishes

Feeding the world in animal proteins, dietary concerns of Western countries and the popularity of Asian cuisine are all reasons to eat fish. Yet, aquaculture has lots of negative points; in order to avoid damages, cages are placed in shallow coastal waters. The excesses of drugs and food are polluting the waters. In addition, exotics fishes can escape from the encloses and enter in competition with the endemics species.

At a time when half of the consuming fishes comes from breeding what solutions do we have for better breeding conditions and thus healthier fish in our plate?

The Ocean Farm Technologies company, created by marine biologists in 2005, claims to have a solution: the Aquapod. This fish cage ball may be carried offshore then be attached to deep sites or drift with the currents, while requiring little human intervention. This innovative system allow significant production of healthy fish in a sustainable and non-polluting way.

The cages are spheres composed of a high number of triangular steel frames. Each frame contains a polyethylene net, made from 80% of recycled products, covered with a wire mesh. This double protection prevents leakage of fishes and predators attacks. Some of them are suitable for receiving, automatic feeding system or an access hatch. The treatment of the steel limits the fixation of planktonic organisms and thus reduces the use of polluting antifouling paint.

Currently, there are 34 Aquapod immersed in the world mostly anchored by long cables in deep water (sometimes between 200 and 300 m). They are fixed as conventional farms, but their impact on the environment is reduced because of the greater depth. Ocean currents can indeed carry and dilute organic waste before they reach the bottom, thus reducing the local pollution. The water cages is also more easily renewed.


We need keep in mind that to reduce significantly the impact on the environment of the fish breeding we need to solve the problem of the food. A quarter of the wild fishes fished is transformed in flours, making the fish breeding contributes to reduce wild populations.

Being vegetarian, I’m not for the intensive breeding, but I support initiatives that tends to improve fish’s life and decreases the impact on the environment.

A squid that doesn’t lack resources

In nature, there is a strong selection pressure pushing animals to blend into their environment or conceal their shape. Here is a small animal that hides in a very unusual way!

The Bobtail Squid or Sepiolida, belongs to the cephalopoda family. Indeed, they are mollusks whose feet is divided in 8 arms and two tentacles that surmount the head.  They are small nocturnal animals which live in shallow waters through the Pacific Ocean and the Indian Ocean. The Bobtail Squid is short-lived, just 3-10 months from egg laid on the undersides of coral ledges to its death.

image credit: scienceray.com

The Bobtail Squid strategy of camouflage is that it beams light from its belly to camouflage its dark shadow from predatory fish on the sea floor. Here’s how :

The main characteristic of the Bobtail Squid is that they have a symbiotic relationship with a bioluminescent bacteria : Vibrio fischery. As in any symbiotic relationship, each protagonist takes advantage of the other. Here, the squid feeds the bacteria with a sugar and amino acids solution. In return, Vibrio fischeri hides the squid’s silhouette when viewed from below by matching  the amount of light hitting the top of the mantle. The squid has developed specialized proteins in its belly that reflect light given off by luminescent bacteria, this gives it camouflage from predators by removing the dark shadow of its body, the squid is masked in its own moonlight glow!

image credit: guardian.co.uk

During the day the Bobtail Squid buries itself in the sand and then covers its peaking eyes with sand heaped up by its tentacles. When it does emerge at night, it keeps a thin layer of sand on top of its body for camouflage as well.


A christmas tree that is worth a look

You haven’t found out your perfect christmas tree ? Let me suggest you the cutest tree you have ever seen :       the christmas tree worm ! 

They belong to the polychaete family and are spread in tropical oceans where they live in coral reefs.

This worms are fixed organisms living in a calcareous tube they secrete for their protection. Their main feature are the two crowns shaped like christmas tree. They are mouth appendages filtering the water and bringing the food caught to the mouth: christmas tree worms are filter feeders. Each spiral is composed of feather-like tentacles called radioles, which are heavily ciliated and cause any prey trapped in them to be transported to the worm’s mouth.

Moreover, radioles are also used for respiration hence they are sometimes called gills. While the worm has no commercial fishery importance, it presents an interest to marine aquarists and divers everywhere. The variously colored crowns make worms extremely popular underwater for photographic subjects for sport divers.

The marvellous hidden corals

A coral reef without hot turquoise sea, sun, and sandy beaches can first appears like bread and Nutella without Nutella. A very sad story you’ll tell me.

But let me tell you about a hidden wonder : the deep-water coral reefs.

Deep-water corals are present in the five oceans from 40 to more than 6 000 meters where the temperature is included between 4 and 10 ° Celsius. The main species are stony corals, able to build real reefs, constantly depositing a calcareous skeleton under their tissues in the same way as shallow-water corals. You can also find gorgones, soft and black corals. Deep-sea corals reefs are real ecosystems, providing habitat and food for many species as sponges, crabs, starfishes, urchins, worms, molluscs, and a lot of vertebrates.

You may know that shallow-sea corals feed themselves thanks to unicellular photosynthetic algae; the zooxanthellae. They live in symbiosis and the zooxanthellae provide to polypes the  photosynthetic products, which feed it.

The question is : How deep-water coral can survive without sun?

Some of them are suspension feeders; the polypes catch directly particles and zooplanktonic organisms in suspension in the current. Secondly, scientists discovered pockmarks, craters in the deep ocean resulting from the release of gas or liquid near a reef. In fact, 60% of the identified deep-sea coral reefs live near or in pockmarks. As pockmarks come from the release of liquid and gas, researchers suppose that there is a link between the deep-water coral reefs existence and the presence of nutrients by seepage through the seafloor (as methane, propane and ethane). This assumption is called « hydraulic theory » for deep-water coral reefs.

The deep-water corals grow more slowly than shallow-water corals, because they do not have zooxanthellae for food. They grow about 10 mm / year instead of 10 to 20 cm / year for shallow-water corals. Estimates of deep-water reef growth is about 1 mm / year. Scientists have estimated through dating methods, some these reefs have at least 10,000 years.

The submarine cables and fishing methods such as bottom trawling tend to break and destroy coral reefs which are very vulnerable because of the slowness of their growth.

The cold-water coral reefs are protected by United Kingdom Biodiversity Action Plan of the Convention on Biological Diversity. The first international conference for deep-water corals held in Halifax, Canada in 2000. Below a video of the symposium which examined all aspects of deep water corals, including methods of protection.


Behind the Cinderella’s glass slipper

You thought you know everything about Cinderella story ?  Let’s check if you know this kind of jelly shoe !

Sea-butterflies belong to the snails family, but they are planktonic organisms. Their scientific name is Thecosomata which is a taxonomic suborder of small pelagic swimming sea gastropods. This term refers to organizations whose body is contained in a cartilaginous shell.

As all planktonic organism, Thecosomata are carried along with the currents. This way of life had led to a number of adaptations in their bodies.

> Sedimentation rate must be very low to prevent these animals sink (they can not really swim). As a result, sea-butterflies have a density close to that of water (containing much water as gelatinous organisms) and they are very small (less than 2cm). Indeed, the more an organization is small, the more the surface / volume ratio is high and the greater the friction forces that apply to it are large, which helps to reduce the sedimentation rate.

> Their foot has taken the form of two wing-like lobes, or parapodia, which propel this little animal through the sea by slow flapping movements.

> To avoid detection by predators, sea-butterflies must be invisible. The shell and the body are totally transparent except a little part; the nucleus which is orange and includes the « heart ».

> For their feeding, they secrete a mucus net. It pastes particles in suspension in the water, then they ingest and digest it.

The gastropod above is called Venus shoe (« sabot de Vénus » in french) because of the shoe shape of the shell. You can find it on beaches, and it was the origin of the story of Cinderella’s glass slipper.

Good luck and see you in 2042

It began on a beach of New Caledonia when 46 Big-headed turtles were found blocked in their  nest while all the others were gone. Volunteers saved them and took care of them in the Aquarium des Lagons. Of the 46 turtles, 43 have survived, the mortality was due to congenital malformations. Big-headed turtles were brushed to allow scientists to fix tags  on their carapace in order to follow their future displacements in the ocean.

In fact, the main cause of the Big-headed turtle death are the fishing nets in which they are caught. Studying their displacements will help scientists to know where this turtles live and thus to spend agreements whith fishermen to protect them.

Pictures are coming from here.

The 20th of October 2012, the 43 turtles were placed in the water during a patrol mission of La Glorieuse.  The mission was conducted in the high sea, somewhere between the New Caledonia and the New Zeland, where the temperature of the water were precisely of 18°C. They have been immersed in the flow they tend to follow without the risk of getting trapped in the lagoon and saving a part of their journey. Few of them have a chance to survive, knowing that one out of 1000 survives in ordinary conditions.

If they are lucky, scientists and volunteers will see them again in 30 years, when they’ll come back on the same beach to lay their eggs.