Coralline algae

Coralline algae are a special kind of red algae that have hard, chalky parts in their cell walls. This makes them feel tough, like rock. They usually come in shades of pink or red, but some can be purple, yellow, blue, white, or gray-green.

These algae often grow on rocks and hard surfaces in shallow ocean areas, especially near the water's edge and in coral reefs. They look like colorful patches covering rocks. Some types can form round balls or grow in bumpy shapes.

Coralline algae are very important for ocean life. Many sea animals, such as sea urchins, parrot fish, limpets, and chitons, eat them. In places like the Mediterranean Sea, these algae help build special reefs called Coralligène, which give many sea creatures a home. There are over 1,600 known types of coralline algae, and most live in salty ocean water, except for one kind that can live in freshwater.

Description

Coralline algae come in two main forms based on how they grow. One form, called geniculate, looks like small, branching trees. These attach to rocks or other hard surfaces either by forming a thin layer or by having root-like structures. They stay flexible because parts of them are not hardened. The other form, nongeniculate, grows as thin to thick crusts on rocks, shells, other algae, or seagrasses. Some of these crusts can be leafy, while others stick very tightly to surfaces. A few types can live freely and roll around.

These algae grow very slowly, adding just a little each year. They all start with a crust-like stage, and some later develop more leaf-like shapes. Their bodies have three layers, and the top layer often breaks off in pieces.

Because coralline algae contain calcium carbonate, they can turn into fossils. They have been used as markers in studying rocks and were even used as building material in ancient Greece. The minerals in their cell walls can change with water temperature, which may affect how well they survive in the ocean.

Evolutionary history

The fossil record of these special types of algae matches what scientists learn from studying their genes. We can find these algae in very old rocks, going back to a time called the Ediacaran. True coralline algae appear in rocks from the Jurassic period and later.

These algae have a good fossil record starting from the Early Cretaceous period. Their fossils help scientists understand when different kinds of these algae first appeared. Some types of these algae change with ocean temperatures, while others are more common when certain fish, like parrotfish, are around.

Habitat

Coralline algae are found in all the world's oceans. They often cover nearly all of the rocky surfaces where they grow. These algae can live in different water depths, from areas that are sometimes out of the water to depths of about 270 meters, where sunlight barely reaches. Some types can survive in water that is not very salty or even in freshwater, though most prefer salty water. They can also handle changes in water clarity and nutrient levels.

Biology

Fresh surfaces are usually covered by thin layers of coralline algae. Over time, these layers can grow thicker or form branches, depending on the surroundings. Sometimes, these algae break off and form small, round nodules called Rhodoliths. Coralline algae are found in many ocean areas, especially in colder places and the Mediterranean Sea. They can live in deep water because they can make their own food even in dim light, sometimes as deep as 268 meters.

Many coralline algae create substances that help certain baby sea creatures, like abalone, settle and grow. This is helpful for both the algae and the baby animals. The algae also provide tiny homes for small sea creatures, helping them stay safe. In coral reefs, coralline algae are very important because they help build and strengthen the reef structure by adding calcium carbonate. They are especially important in areas with strong waves, where they help protect the coast by reducing erosion.

Relation to humans

The first coralline alga recognized as a living organism was probably Corallina in the 1st century AD. In 1837, Rodolfo Amando Philippi recognized coralline algae were not animals, and he proposed the two generic names Lithophyllum and Lithothamnion as Lithothamnium.

Because of their hard structure, coralline algae have several useful purposes. In Britain and France, large amounts of certain types of coralline algae are collected each year to help improve soil.

Coralline algae are also used in making dental implants and as a food additive for farm animals. They are popular in home aquariums because they add color and help keep the water clean.