There are approximately nine hundred species, distributed throughout the planet's seas and oceans, where they play a fundamental role in the balance of all marine habitats. These are sea urchins, organisms as small as they are complex, which over hundreds of millions of years have been able to adapt to the most diverse living conditions in nature. However, they are highly sensitive to climate change and, due to their calcareous dermal skeleton, to increasing ocean acidification. This is without even considering the effects of indiscriminate harvesting for food on the most exposed and declining populations.

Sea urchins are invertebrates belonging to the echinoderm phylum, along with starfish, sea lilies, brittle stars and sea cucumbers. They share, at some stages of their life, the characteristic of pentaray symmetry and the presence of a dermal skeleton composed of calcareous plates that, in sea urchins, are welded together to form a rigid shell. The plates are also capable of regenerating if partially damaged. The dermal skeleton features the long, mobile spines characteristic of sea urchins, while the ventral ambulacral pedicels protrude from the sea urchin's abdomen, allowing the animal to move, thanks to an internal aquifer system "fed" by seawater.

Sea urchins are classified into regular and irregular echinoids. Originally, they were all regular, meaning they had a spherical shape, pentaradial symmetry, anus facing upwards and mouthparts symmetrically downwards, to allow the animals to graze on the (widely varying) seabeds where they live, as benthic organisms. Regular echinoids are still the most numerous, but starting in the Jurassic, a differentiation occurred. This gave rise to the irregular echinoid species, with heart-shaped or flattened shapes and a characteristic bilateral symmetry, with the anus and mouth positioned obliquely rather than mirroring each other. The mouth, however, is in contact with the sandy or muddy substrate, in which they burrow and take refuge.

Regular echinoids are characterized by a spherical theca that is externally divided into ten sectors: five ambulacral areas, from which the pedicels emerge, and another five interambulacral areas, from which the gametes emerge. The largest of these areas is called the madreporite and has holes to allow the passage of seawater. This serves to operate the aquifer system, which allows the urchin to move, activating the release of the numerous ambulacral pedicels from the theca, which may end in suckers for better adhesion to the substrate. In irregular echinoids, the ambulacral areas are called "petaloid" due to their distinctive petal shape.

The downward-facing mouthparts contain the animal's feeding organ. This organ is called "Aristotle's lantern" because the Greek philosopher was the first to identify and describe it. It consists of five calcareous plates, shaped like a pyramid with the base pointing upward, connected by muscle bundles. The five teeth, located in the pyramids, protrude through these plates. These teeth are used by the animal to scrape the substrate, literally grazing on rocky seabeds, among seaweed beds, or in seagrass meadows. The gills are located in the area around the mouth.

Sea urchins feed primarily on plants, bits of algae, or Posidonia oceanica leaves and other marine plants, but, depending on the food availability in their areas, they may also consume small animals or animal debris. The primary ecological function of sea urchins in the world's seas is linked precisely to their role in the food chain: by feeding on plants, especially algae, they prevent the proliferation that is harmful to the balance of coral reefs and coralligenous seabeds. They are also important as food for other marine animals. Given the hardness of their shells, sea urchins are preyed upon only by sharp-toothed fish such as gilt-head bream and white sea bream, but they can also be eaten by large crustaceans, mollusks, and even starfish, their relatives.

Males and females are identical, making them indistinguishable. Both release their gametes simultaneously into the sea, where fertilization occurs. The larvae, known as "plutei," are characterized by bilateral symmetry and have between six and eight pairs of arms equipped with ciliated bands with which they feed and move through the water column: they are, in fact, planktonic organisms. Only at the end of this phase, which lasts a few months, do the plutei settle on the seabed, where their adult life as benthic organisms begins.

When it emerges grayish white from the egg, its webbed feet are already pink. Like its beak, still very short, to allow it to be nourished by the long curved beak of its parents with the milky and extremely nutritious substance that they produce from special glands, during the period of raising their only chick. It is quite precocious and does not stay long in the nest, where the adults take turns caring for it, to go and get food. But even with the appearance of the juvenile plumage, the chick of the Phoenicoprterus roseus remains predominantly white, although the first gray and black feathers also begin to stand out. Black will forever remain the color of all the powerful flight feathers, thanks to which it will be able to complete its long seasonal migrations. The rest of the large body with the long neck will gradually acquire, increasingly marked with age, the spectacular characteristic coloration of the pink flamingo.

The distinctive color, in the adult phase, is declined in the most varied tones and shades, from the most delicate of the plumage to the more decisive, even in some places gaudy, of the wing coverts, depending on the age, the different parts of the body and above all the food that the flamingos feed on. Yes, because the pink and its gradation depend on the diet, in particular on the availability in their diet of small crustaceans such as Artemia salina rich in carotenoids, which are deposited in the feathers coloring them.

Among the six species of flamingos existing in the world, the pink one lives in the Mediterranean, as well as in the rest of Europe, in Africa and in Asia. In Italy, it is estimated that at least 15 thousand individuals are sedentary, thousands more arrive with seasonal migrations and populate the ponds of Sardinia, the salt pans of Trapani and the nearby Egadi, other wetlands also near Marine Protected Areas. Its habitat coincides precisely with the coastal wetlands, where there are shallow and brackish waters.

These are social birds, which gather in colonies of thousands of individuals, especially during the spring nesting periods, when they meet in the chosen areas, not necessarily always the same ones, where they find the best conditions for reproduction, preceded by complex group nuptial displays. They are monogamous and each couple builds its own conical mud nest, where it lays a single egg. And always together, the male and female take care of the incubation and, after hatching, of the raising of the single chick that, after about ten days, leaves the nest to join other peers in large groups looked after by a few adults, allowing the others to move in search of food. The first flights of the chicks begin around two months, while they reach sexual maturity in the second or third year of life, when the pink of the livery becomes more evident.

The long curved beak, fuchsia pink with a black tip, is shaped so that it filters the water through special lamellae that it expels after having retained crustaceans, bivalves, annelids and larvae, small blue-green algae, seeds and plant fragments. It can also use very salty water, such as in salt marshes, since it is equipped like other sea birds with a salt gland, which allows it to expel excess salt from the nose. Another fundamental gland (uropygial) is located above the tail and secretes sebum, in this case also containing beta-carotene, which the animal spreads with its beak on the plumage, after having carefully cleaned and washed it, to restore its impermeability. With this operation, flamingos also revive the pink/reddish color.

At rest, flamingos often stand on one leg, while the other is drawn up against their body. The usefulness of this behavior is not yet understood. But they are migratory birds, which make long and frequent journeys throughout the year, thanks to their powerful wings and a wingspan that in adult males can exceed one and a half meters. And watching them as they slowly take flight or while they are traveling, unmistakable for their color, is an unforgettable spectacle.

Due to the risk of loss of their habitat, flamingos are an internationally protected species by the EU Birds Directive and the Barcelona and Bern Conventions.

The element that most distinguishes it even to the least expert eye, so much so that it is included in its common name, is a tuft of curved feathers on the head that is part of the male's nuptial plumage.

The flight is long and demanding, the search frantic. Every day, when the color of the night gives way to the first light of dawn, until the setting sun floods the surface of the sea with gold.

If it were not always on the move, while it explores the shoreline with its long beak in search of food, its livery and size would make it impossible to distinguish it in the expanse of sand. 

In the wild and sheltered rocky ravines of the islet of Vivara, they can nest undisturbed and contribute to the survival of their species, which is still in danger.