La VIE AQUATIQUE à Port Grimaud

AQUATIC LIFE in Port Grimaud :

Natacha LAMY, a doctor in marine biology and a resident of the lakeside town since 2023, is fascinated by what goes on underwater, an aquatic life that exists without us even realising it, a life that came into being thanks to the creation of the jetties at the entrance to the town. A life that has settled on the riprap and thanks to the riprap to offer itself a living environment and a peaceful existence sheltered from the gaze and ignorance of humans. A life that is now part of the long history of the lakeside town.
This page is dedicated to his research, which deserves to be known by residents :

Natacha presents her underwater activity, observing, discovering and photographing the underwater life that has taken over the rocks of the large jetty at the entrance to the city :

Presentation :

       " Let me start by introducing myself. I've been swimming with a mask and fins since I was a kid. A few years ago, I bought a little underwater camera and a red buoy that I carry around behind it to mark my position. I love going along the coast. I wrote my thesis on the organisation of macrobenthic communities in an oyster bed in the Etang de Thau (Hérault). The macrobenthos is everything that lives on the seabed and is visible to the naked eye.

So I'm a benthologist.

       After the Hérault, I lived with my little family in Guadeloupe. Over there, I had a great time on the coral reefs and with the sea turtles, which don't belong to the Benthos, of course. Since then, I've kept a close eye on the sands of Port Grimaud, hoping one day to see their characteristic tracks again;

       As I get bored in front of the beach, I had the idea of regularly exploring the jetty. All in all, it makes sense to me, as the pier is made up of upright hard substrates and sand at the foot… The pier is therefore made up of blocks of poured concrete and granite. These hard substrates provide a large surface area for colonisation (algal felting and encrusting coralligenous).

       There is a very important thesis that has enabled me to confirm what I was seeing: that of Sandrine Ruitton, Professor at the Université de la Méditerranée: ‘Les communautés benthiques et nectobenthiques associés aux aménagements littoraux en Méditerranée nord-occidentale. Structure et fonctionnement’, 1999.

       The stacking of boulders here creates a variety of depths, habitats and shelters or refuges (in the interstices) for benthic invertebrates and fish. The populations of these blocks are dominated by grazers or scrapers, such as sea urchins, limpets, purpins, juvenile saupes and other benthophagous fish (sars, etc.). In the vicinity of this jetty, we can also observe planktonophagous open-water fish (joels, oblades…), always attracted by a wealth of particles and organic matter in the water column. There are also predators, such as wolves. At the foot of the jetty, sand and mattes are home to red mullet and rock bass.

       In many fish species, juveniles and adults live together. They are then considered to be in a recruitment phase.
       Looking at the Gulf of Saint Tropez alone, the anthropogenic (human) pressures on all the marine waters of the Gulf are numerous. They affect the benthic populations, those of the rocky and soft bottoms, which are altered. And also on the Posidonia in the open sea.

       The current bio-colonisation seen on the blocks is the same age as the jetty: a wonderful balance has been achieved over 50 years... The jetty and the canals are a great nursery. There will be nothing to eat for a very long time if we destroy this jetty.

the pier is alive, an oasis...

       There are lots of juveniles, in the company of adults... This means that recruitment is a fact, and that's important, because populations are renewed

       The balance observed to date at the jetty remains fragile, at the mercy of disruption when the source populations can no longer produce larvae. In addition, natural areas on all coasts are fragmented and species with a low dispersal capacity can have problems.
       So this breakwater at the very bottom of the gulf is an opportunity for restocking because it is conducive to recruitment.

       Let's discover these little animals together… :

The pier :

Composition

       The jetty is made up of 60 tonnes of sheet piling, 250m3 of poured concrete and granite blocks, each weighing between 5 and 7 tonnes, from the quarry on the Route du Plan-de-la-Tour.
      It took 22 lorries doing ten shifts a day to move 24,000 tonnes of riprap...
      The jetty is 126m long and can be moored along 120m of the entrance channel. Dredging the channel represents 12,000 m3 of sand to be removed and transported.

     It was in the middle of these huge blocks of rock that aquatic life appeared. And this is the field of research chosen by Natacha LAMY.

     Along this pier, she has discovered blennies, Trypterygions, and many other species that she intends to introduce to us...

The BLENNIES :

Benthic fish are those that live on or near the seabed (benthos refers to the nekton or plankton in the water column)..

" They are small benthic fish with a fin on their back. They are opportunists because they ‘comb’ wide, or rather they eat what they find! A bit of everything... Seaweed, crustaceans, molluscs, etc..."

Website explaining benthos, pelagos, etc.

5 photos to discover these blennies :

Blennie dalmate

Dalmatian blennie in its hole

Blennies diabolo

Blennie from Caneva

Blennie-sphinx

Palelles, burdocks and blennies

The TRYPTERYGIONS :

BR>        " Two species of Tryptérygion can be found in the rocks along the pier: the yellow Tryptérygion (Tripterygion delaisi) and the red Tryptérygion (Tripterygion tripteronotum) and the red Tryptérygion (Tripterygion tripteronotum.)
       Yellow’ females have a dark black bar at the base of their tail, while “red” females have a bar similar to the others.
       To quickly differentiate Tryptérygions from Blennies in the water, I call them ‘Pointed Snouts’! These sedentary fish have three fins. They feed on small crustaceans and planktonic micro-organisms..."

A Female ‘red’ trypterygium

Triptenigyon jaune

A female ‘yellow’ Tryptérygion

Triptenigyon rouge andalou

Other Trypterygium

Other species :

       " I often come across these three species, which are more or less the same size, at the foot of the pier or near it, and they have different feeding strategies " :

     - The Crenilabre-paon swallows invertebrates with a mouthful of algae.
     - The Barbarin (or red mullet) digs in the sand for worms and crustaceans.
     - The Serran écriture (recognisable by the lines drawn on its head) stalks to catch small fish, crustaceans or molluscs.

The Crénilabre-paon and the Barbarin

Le Serran

The Serran écriture

the kings of camouflage :

      Natacha LAMY doesn't dive in all weathers " I need sunshine and clear, calm waters for my photos " she explains :
      " The kings of camouflage are fish that she has spotted in the water of our canals, ‘ Fish that hunt on the lookout, that blend in with the environment... Difficult to flush out " :
     The Gobie moucheté (with its V-shaped “snout” line)
     The Gobie céphalote (with his big head)
     The Brown scorpion fish
     Mediterranean rhombou (flatfish)

The Gobie moucheté

Le gobie céphalote

The Gobie céphalote

La rascasse brune

Brown scorpion fish

La rascasse brune

The Mediterranean rhombou

They enjoy our canals :

       Some fish " enjoy our canals... " :

     - The gilthead sea bream "(recognisable by the bar on the operculum and the golden band on the forehead) is a crusher of shells and carapaces",
     - Sars "have well-developed teeth and a slightly protruding mouth* for catching prey",
     - The sea bass, "very shy and solitary... It is a good indicator of the quality of coastal marine ecosystems"...

     ( * Protractile; Refers to an organ that elongates of its own accord. (By extension) Mouth of certain fish (mainly bottom-dwelling fish) that can elongate forwards and then retract, making it possible to poke around in sand and sediment..)

The gilthead sea bream

Le sar

The Sar

The sea bass

Predators and carnivores :

In ecology, predators are those that hunt, whether lying in wait or not, and catch animal prey smaller than themselves...

" Predators, or carnivores, include sea bream, sea bass, gilthead seabream (adults), molluscs such as the bloody purple and the fasciated rock and, of course, cuttlefish... And the comb star."

Le Pourpre bouche de sang

La Seiche commune

L'Etoile Peigne

Interstitial spaces :

       " Before going on to other species and invertebrates, here are some photos of the interstitial spaces between the blocks...
     The surfaces have been colonised over time, since the creation of the jetty... There are those that are directly exposed to the currents and waves, and then there are the interstices that provide shelter for fauna and algae...
     All these surfaces are a source of food for the animals' diet " :

The underwater part of the pier

Surface extérieure

Other view...

Surface extérieure

Aquatic beauty...

Exposed surfaces :

     " The outer surfaces of the blocks are more exposed to hydrodynamic forces. Algal felting and encrusting coralligenous can be observed. Grazers (such as saupes and molluscs) limit the expansion of the algae. Competition for space also leads epibiont organisms to attach themselves to the shells of limpets and other algae. "...

     Algal felting is a more or less extensive covering of small algae.
     Coralligenous encrusting algae are initially calcareous algae that encrust in the interstices, holes, etc, of hard substrates (in this case boulders) and on which all sorts of colonies can develop... The coralligenous in the Mediterranean is as important a source of biodiversity as the Posidonia meadows....
     Epibionts are living things that live on other living things (always on the surface), as opposed to parasites, for example, which live in other people's bodies. When you look at an oyster shell, there's a whole host of flora and fauna on it! There can be an interaction between the host and the epibiont. One provides protection and the other food....

Gregarious fish :

       Gregarious fish are varieties that live close to the jetty, grouping together. Wolffish hunt alone. Saups gather in shoals.
     " The mullets we see in the canals feed on algae and small invertebrates...
     Golden mullets like rocks, lagoons and estuaries (but not freshwater).
     Spoonbills are the most common at sea. Their young enter lagoons, estuaries and sometimes freshwater...

     Saupes graze on seaweed.

     From the seabed to the surface: The marbled shark lives exclusively on the sandy seabed and the Oblade in open water, but close to the rocky seabed and seagrass beds " :

Golden mullets

Mulets lippus

Spoonbills

les Saupes

Saupes

marbled shark

Loup de mer

Wolffish

Grazers :

"The most abundant grazers here are black sea urchins, blue limpets and gibbous toupies... Look closely at the photos... You can see the purple marks left behind by the limpets after grazing. And the limit of extension of the algal felting in front of the sea urchins and limpets."... :

Black sea urchins

Patelles bleues

Blue limpets

Gibbule toupie

Gibbous toupies

Oursin et patelle

Sea urchin and limpet

The Cnidaires... :

" Among the Cnidaria, we note the presence of the Green Aiptasia, the Mooring Hydraria and, carried along by the currents, the beach-goers' favourite, the Pelagia noctiluca (the pelagic jellyfish). ..."...

Green Aiptasia

Hydraire des Amarres

Mooring Hydraria

Pelagia noctiluca

Pelagic jellyfish

The filterers... :

       Filter feeders feed on very small organisms. They are sometimes also called suspension feeders. They are equipped with a system that filters the water to capture only the micro-organisms. Natacha introduces us to the filter feeders she spotted on the large pier :

       " The flat oyster, Ostrea edulis, whose ‘status is a cause for concern, as it plays a major ecological role in the areas where it becomes established: it has been described as an “ingenious” species because of its ability to colonise the seabed and thus create a favourable environment for the development of other marine species’ (pecheapied-loisir)...
       Tube worms, such as Sabella and sprirorbia...
       The Crambe crambe sponge, which can cover itself with the shells of molluscs such as Arca noae, Noah's Ark... In this case, if you get too close, the Ark closes and the sponge moves ! "...

The flat oyster

Sabella

Sprirorbia

Eponges Crambe crambe

Crambe crambe sponge