The Halimeda tuna is a green marine algae of the Halimedacae family. Halimeda tuna alga marina verde famiglia Halimedacae intotheblue.it
It appears as a chain of “round leaves” joined; it is fixed to the rocky substratum with thin rhizoids.
The color is green or yellowish-green, sometimes whitish due to the presence of limescale deposits.
It is present throughout the Mediterranean Sea but also in the Atlantic Ocean, the Pacific Ocean and the Indian Ocean. It is a typical algae of the coralligenous environment that tolerates light at low intensity, but it is possible to observe it even a few meters deep.
Halimeda tuna is a calcareous green seaweed, attached to the seabed by a holdfast. Each individual thallus (frond) consists of a single cell forming a tube with multiple cell nuclei. The cytoplasm is mobile and the nuclei, chloroplasts and other cell contents are free to move around inside the cell wall. The tube has flattened, disc-like segments connected by flexible joints. The surface of these segments have swollen areas called utricles which together make a tabular “cellular pavement“.
Below and between these utricles, there are gaps and it is here that the fluid is saturated with calcium carbonate and crystalline needles of aragonite form. These stiffen the segments and make the seaweed unpalatable to fish. When the seaweed dies, this skeletal material breaks down into “sand”. Members of this genus are likely to be one of the most important agents of calcification in the marine environment, considerably more productive in tropical seas than stony corals.
This species is found in the tropical and subtropical Indo-Pacific region, the Mediterranean Sea and the western Atlantic Ocean. It grows on rocky reefs from the shallow subtidal zone down to depths of about 70 m (230 ft). In the Mediterranean Sea it occurs in two separate habitat types; shallow, warm lagoons and sheltered places in the central Mediterranean and deep water (18 m (60 ft)) rocky habitats in the northwest Mediterranean. Similarly, in the Florida Keys, it is the dominant green alga in shallow back reef locations and in much deeper, less well lit, reef slope habitats. Halimeda tuna alga marina verde famiglia Halimedacae intotheblue.it