There is a moment, in September, when the sea below Boccadasse becomes strangely transparent. The last summer heat subsides, the northwesterly wind cleanses the air, and looking from the edge of the rocks you can see all the way to the bottom: the white gravel, the crabs walking sideways, and then — a few meters further — a dark, dense shadow stretching out like a meadow. It is not a shadow. It is life. It is a seagrass meadow.
Most swimmers don’t know what it’s called. Some call it seaweed, some call it “that green stuff,” some push it away with their feet as if it were dirty. Instead, it is one of the oldest and most precious plants in the Mediterranean — a real plant, with roots, stems, leaves and even flowers — and without it, the Ligurian beaches would not exist in the way we know them. This is not rhetoric: it is biology applied to the territory we inhabit.
To talk about posidonia is to talk about Genoa’s sea from a point of view that is rarely spoken aloud. An underwater perspective, patient, millennia-old. And perhaps necessary, now more than ever.
What is posidonia: a plant, not an alga
The first misunderstanding to clear up is this: Posidonia oceanica is not an alga. It is an angiosperm plant — the same botanical category as rosebushes and wheat fields — that has adapted to live underwater over the course of millions of years. It has real roots that anchor the seafloor, a short rhizomatous stem that can be tens of thousands of years old, ribbon-like leaves of intense green that can exceed one meter in length, and in autumn it produces small green flowers gathered in spikes. Flowers, under the sea. It is one of those things that, when you discover them, change the way you look at the Mediterranean.
The name comes from Poseidon, the Greek god of the sea — a tribute to the silent majesty of this plant that colonizes sandy seabeds between three and forty meters deep. In the Portofino marine protected area, between Santa Margherita Ligure and the promontory, posidonia meadows cover considerable areas and are among the best preserved in the Ligurian Sea. It is here that marine biologists from the AMP conduct periodic monitoring campaigns, measuring the density of leaf bundles and the health status of the matte — the technical term for the compact layer of roots and organic matter that the plant accumulates over time.
The matte is, in a sense, the heart of posidonia: a thick, hard, almost stony layer that forms slowly at a rate of about one millimeter per year. A mature posidonia meadow can have a matte as deep as one and a half meters — which means that those compacted roots represent more than a thousand years of uninterrupted growth. Treading on a posidonia meadow, with flippers or a rubber dinghy’s anchor, is equivalent to destroying in a few minutes something that nature has built over the course of human generations.
Why posidonia is essential for the marine and coastal ecosystem
To say that posidonia is important for the ecosystem is almost an understatement. It is more accurate to say that without it the Mediterranean — at least in its coastal areas — would be a much poorer, more unstable place, and in the long run, less livable even for us.
The first role is that of marine nursery: posidonia meadows are the nursery of the Ligurian Sea. Among the leaves, larvae of many fish species find shelter, sea urchins, starfish, shrimp, young cephalopods. The fish wealth that the fishermen of Boccadasse and Nervi know well — gilt-head bream, sea bream, blenny, rabbitfish — depends largely on the integrity of these meadows. A healthy meadow produces up to twenty liters of oxygen per square meter per day: more than any terrestrial forest, proportionally.
The second role is that of coastal protection. The long, flexible leaves slow down the force of the waves before they reach the shore, reducing beach erosion. The banquettes — the cushions of dry leaves that accumulate on the shore after autumn storms — are not waste to be removed: they are a natural barrier that protects the sand from winter washaway. In years when coastal municipalities have had banquettes mechanically removed for aesthetic reasons (beaches “cleaner” for tourists), the beaches have lost sand measurably. Nature was not dirty: it was simply doing its job.
The third role is that of carbon absorption. Posidonia meadows are among the so-called “blue carbon ecosystems” — marine habitats that sequester carbon from the atmospheric cycle and store it in the matte for centuries. It is estimated that Mediterranean posidonia can sequester up to 83 grams of carbon per square meter per year: data that has attracted the attention of climate researchers, in addition to marine biologists.
The meadows in the Portofino Marine Protected Area
To see a posidonia meadow in good health in the Ligurian Sea, you don’t need to go far. The Portofino Marine Protected Area — established in 1999 and protecting the seafloor of the Portofino promontory between Camogli and Santa Margherita Ligure — hosts some of the best-preserved meadows in Liguria. Zone A, the integral protection zone where any activity is prohibited except scientific research, extends around the seabeds of Punta Chiappa, in Camogli, and includes stretches of meadow that monitoring indicates as stable or slowly improving.
Guided scuba dives in zones B and C of the MPA allow you to observe the meadows up close, following marked routes and accompanied by certified guides. The visibility of the Ligurian Sea in autumn and spring — when summer plankton disperses — can exceed twenty meters, and a descent into a seagrass meadow under these conditions is a visual experience difficult to forget: the dark green of the leaves swaying slowly, fish gliding between the vegetation ribbons, light filtering from above in oblique rays. It is a silent and absolute landscape.
Those who don’t dive with tanks can observe seagrass with snorkel and mask in the shallow waters of some coves on the headland, or — with some luck and calm water — simply by looking from the edge of a boat. At Punta Chiappa, the small fishing village reachable on foot from Camogli along the coastal path, the rocky seabed descends steeply and seagrass grows thick just a few meters below the surface. It is one of those places where the boundary between the above-water and underwater worlds thins until it almost disappears.
How to recognize seagrass: leaves, matte and banquettes
Recognizing seagrass doesn’t require a course in marine biology. A few simple observations are enough, ones that become automatic after the first time.
In the water, seagrass appears as a dense meadow of ribbon-like leaves, dark green in color (more intense in summer, lighter in spring), swaying with the water’s movement. The leaves are arranged in tufts, bound at the base by a short stem. The seabed around the meadow is often sandy or mixed sand-gravel; the matte, when exposed by seabed erosion, appears as a hard, dark, almost peaty layer. It doesn’t resemble filamentous algae or the green felt of rocks: it is more structured, more solid, unmistakably vegetable.
On the shore, seagrass appears in the form of dry leaves, brown-orange in color, which the sea pushes onto the beach after storms. In autumn and winter, Ligurian beaches are covered with these deposits. In some cases, true banquettes form: compact cordons of interwoven leaves and fibers, sometimes as high as half a meter, which may seem like an obstacle but actually retain sand and protect the beach from erosion. A beach with banquettes is a healthy beach — even if it’s not the postcard image we would expect.
There is also another unmistakable sign of seagrass: egagropiles, small fibrous gray-brown spheres found on Ligurian beaches that look like felt balls. They are formed from the remains of seagrass leaves, compacted by the action of currents: a natural waste product that harms no one, and which children often collect thinking it is something mysterious. In a sense, it is.
The sea of Genoa’s people and respect for what cannot be seen
The people of Genoa have a relationship with the sea that is unlike that of any other Italian city. It is not the festive and Mediterranean relationship of the south, nor the Nordic and sporting relationship of Atlantic ports. It is something more everyday and less declared: a continuous presence, almost assumed. In the morning at Lido di Albaro before heading to the office, on Sunday at Boccadasse watching the boats, in the evening on the Corso Italia waterfront with the sound of the sea in the background.
In this daily routine, seagrass is almost invisible. Swimmers perceive it as a nuisance — the leaves that touch your legs while swimming, the dried leaves that “dirty” the beach — without knowing that they’re swimming above an ecosystem that is older than many Genoese cathedrals. The elderly fishermen, those who still head out early in the morning from the Nervi marina or the Boccadasse waterfront, know it very well: they know where the meadows are, they know that fish are more abundant there, they know that where seagrass disappears the seabed becomes impoverished. It’s practical knowledge, not scientific, but it reaches the same conclusion.
In recent years, awareness is growing even among non-specialists. The awareness campaigns of the Portofino MPA, educational activities in Genoa’s schools, documentaries produced by Golfo Paradiso and other local organizations are helping to make seagrass something known — not just by environmentalists, but by families who take their children to the sea on Saturdays. It’s a slow change, like the growth of the seagrass bed itself, but real.
Practical tips: how to behave with seagrass
Respecting seagrass doesn’t require heroic gestures. It requires a few simple precautions that, if adopted by everyone, make a concrete difference.
- Don’t anchor on seagrass: if you have a boat or speedboat, use fixed buoys where available (the Portofino MPA has installed numerous ones) or anchor on bare sand, making sure your anchor doesn’t drag over seagrass. An anchor that scrapes a meadow damages it irreversibly.
- Don’t walk on the seabed: in shallow waters, avoid walking on seagrass meadows with fins or bare feet. The seabed is fragile: repeated steps over time are enough to create a “scar” that takes decades to heal.
- Don’t remove dried leaves: if you frequent a public beach, leave the dried leaves where they are. They’ll protect the sand during winter storms better than any coastal engineering structure.
- Observe, don’t touch: during dives or snorkeling, observe the meadow without leaning on it. The leaves break easily and every damage is a permanent loss for that millimetric growth cycle.
- Report abnormalities: if you notice patches of dead seagrass, abandoned nets around seagrass or illegal moorings, you can report it to the Portofino MPA or the Coast Guard. Community monitoring works.
For those who want to explore the topic with a guided dive, the diving centers authorized by the MPA — such as Portofino Divers in Santa Margherita Ligure and the B&B Diving Center in Camogli — offer specific trips to observe the meadows in the MPA, with certified guides who explain underwater what no book can convey with the same clarity. Family snorkeling trips in summer are accessible to children from six years old.
If you prefer to observe posidonia from the surface, the boats of Golfo Paradiso — which connect Genoa, Recco, Camogli and Portofino from April to October — pass over seabeds where the meadow is clearly visible on calm days with good light. No equipment required, just a bit of attention and a curious glance downward.
The sea we see from the shore is only the surface. What really matters — the life, the balance, the history of millions of years — is hidden below, in those dark and silent meadows that breathe slowly on the bottom. Knowing them is, in a way, already protecting them.
If Genoa is calling you — with its rough and authentic sea, with its seabeds that hold stories older than the city itself — the homes of genovabb.it are the right starting point. Some overlook the waterfront of Boccadasse, others are in the heart of the Historic Center just steps from Porto Antico, still others in Nervi, where the Anita Garibaldi promenade walks along the sea every morning. You can book your stay and take home something that cannot be bought in souvenir shops: the awareness of a sea worth respecting.
