Estuaries are areas of great natural beauty, where rivers meet sea water. Strongly conditioned by the tides, they are considered areas of transition between freshwater and marine habitats.
Estuaries function as a kind of maternity ward, i.e. a place that fosters the growth of juveniles of many fish species, such as sea bass and sea bream, which find there the ideal conditions for development in terms of food and protection.
On the other hand, as mud or silt is not as permeable as sand, water, which carries oxygen and food, does not circulate easily, requiring animals that live in the substrate to make special adaptations in order to survive. However, they are home to a huge variety of animals, particularly species that can dig galleries or burrows where they spend most of their time, sheltering themselves from the different aggressions of the environment.
LIVING IN MUD OR SAND
The mud or sand that make up the substrate of estuaries is favourable for animals to settle, forcing those that live on the bottom to develop special adaptations in order to survive. Some species dig galleries or burrows where they spend most of their time, sheltering themselves from different aggressions. Others, such as flounders, perfect their camouflage techniques by burying themselves in the sand, with which they blend in.
Tube dwelling anenome - It lives in a tube, which can reach 1 metre in length and is buried in the sand, built from solidified mucus combined with particles from the bottom (grains of sand, pieces of shell, algae, etc.). The animal moves freely inside this tube, where it takes refuge whenever it feels threatened.
Scallop - To hide in the bottom, the scallop takes advantage of the water it squirts out of the back of its shell to dig a hole in the sediment. It then takes shelter by covering itself with grains of sand or mud, thus managing to go unnoticed by its enemies.
Finger-shaped sea pen - The round sea pen is a colonial animal, like corals, gorgonia, and sea fans. It lives on sandy bottoms, from the lower limit of low tide to deeper areas, and is capable of digging itself out when covered in sand and reattaching itself to the substrate when dislodged. It consists of a large, fleshy, stem-shaped central polyp whose base burrows into the sand.