Well... maybe it's because I've been in the water for a while but the water is starting to get really cold, I can barely feel my hands.I look at the dive computer, which tells me that it's a whopping 15°C around me! Obviously, this temperature might be acceptable on land, but underwater, 15°C is a temperature not to be underestimated.
I think this temperature is due to the fact that I am quite deep (but obviously never below 40 meters!!) and therefore I rise towards the surface but even at 5 meters deep the temperature remains constant at 15°C.
This condition of constant temperature along the entire water column occurs from February to April, and is due to a summer phenomenon called thermocline.
In summer, solar radiation heats the surface layers to temperatures of up to 25/26°C, floating on the deeper waters (which always maintain a temperature of 12/13°C) because they have a lower density.
The thermocline
The thermocline is nothing more than an imaginary line of demarcation between these two layers, and it is very recognizable underwater, partly because of the sharp difference in temperature and partly because of the optical effect known as the fata morgana, the same one you see on the highway in the middle of August when the scorching sun heats the asphalt.
Clear?!?!?!
This happens in summer. In winter, as surface water cools, its density also increases and therefore tends to sink to the depths. When the density of surface water exceeds that of deep water, mixing occurs. Surface water, rich in oxygen but poor in nutrients, sinks (downwelling), and deep water, rich in nutrients but poor in oxygen, rises (upwelling).
This is why the temperature in winter is decidedly cold but constant along the entire water column and why in summer the thermocline phenomenon occurs.
Having completed this quick, but necessary, excursus on the temperature of our sea, I return to greater depths, since the temperature does not change!
I turn around and find myself almost face to face with a very strange fish with an eye in the middle of its body. I immediately think that if that is the eye, it must be a very large fish. But then I focus my attention and in an instant my studies of marine biology take hold, making me immediately recognize a beautiful specimen of John Dory (Zeus faber).
John Dory fish
Actually, I wasn't wrong; the spot in the center of the body that I mistook for an eye is a sort of defense of this fish, as it confuses predators who, mistaking it for an eye (precisely!!), tend to consider the specimen to be much larger than it actually is.
The John Dory is easily recognizable underwater by its distinctive shape: a laterally compressed, very tall, and oval-shaped body. The head has an almost triangular profile with large eyes and a protractile mouth. From the base of the head, eight to ten very long dorsal spines arise, forming the first portion of the dorsal fin, while the second portion is symmetrical to the anal fin, small and transparent.
It has a silver color with golden shades and the presence of a large circular black spot, surrounded by light, on each side of the animal.
It's typically a solitary animal and is typical of this month of the year as it prefers very cold waters. In summer, it moves to depths inaccessible to us divers.
Legend has it that the two black spots on its back are the footprints of Saint Peter when, at Jesus' request, he took the fish in his hand to extract a coin from its mouth.
I leave the John Dory to be admired by the other inhabitants of the sea and move towards the surface ready to emerge when I see hidden in the sand, very well camouflaged, an extremely ugly and strange fish!!!
It's an anglerfish (Lophius piscatorius) !!!
Monkfish
A fish with an extremely flat body and broad anteriorly. Immediately noticeable features include a broad head, protruding eyes, and a large, upward-facing mouth with curved teeth.
It has two dorsal fins: the first has spiny rays, the first of which is much longer than the others (called the ilium), which it uses like a fishing line to attract prey; the second dorsal fin, however, is large and made up of soft rays.
It has an extremely camouflaged coloration especially for the type of environment it inhabits, it is brown with reddish shades and patterns.
It is a long-lived animal, reproduction occurs in winter and there are different times of sexual maturity for males and females: the former reach sexual maturity at 6 years, the latter at 14.
It is absolutely harmless to humans and its flesh is discreet as long as it is not infested with TapewormThe commonly edible part is usually the tail (monkfish).
Well, I met two very strange and fascinating animals. They're typical of the months from February to April, so you have to take advantage of them... but right now it's decidedly cold.
Sorry, I'm going out and I'll see you later!
