Coral inhabitants

Extraordinary algae and plants
The coral structure offers a surprising variety of habitats for plants and animals. In addition to the algae that live within corals, the vegetal world also includes a large number of red algae, such as the encrusting alga Porolithon of the Asian Pacific area or some green algae, such as the Caulerpa. It has been calculated that 1-5 kgs of algae per square metre are produced every year in the reef. Lagoons and sheltered sandy areas are also home to such water plants as the Thalassodendron, which forms underwater prairies like those of the Mediterranean Posidonia, a plant loved by sea turtles as well.
Colourful inhabitants of the reef
Very many are the herbivore animals feeding on the plants that grow in the reef: sea urchins, crustaceans, molluscs and a number of species of fish. Parrot fishes (so called for their strong beak-shaped mouth) and surgeon fishes (so called due to the presence of a lamella as sharp as a scalpel on their tail) are the main herbivores. The mouth of the parrot fish is specialised in taking seaweed off the coral surface, leaving unmistakable marks of their passage. In this way, they also take off the surface layer of the calcareous skeleton, which, undigested, is then expelled in the form of coral sand.
Other big coral eaters are the prickly starfish Acanthaster; if many individuals of this species concentrate in one area, they can seriously damage the reef.
The sea worm Hermodice caruncolata that lives in the Caribbean can devour one square centimetre of coral in an hour; the lionfish too (such as flag lionfish) mainly feed on coral polyps and other small animals they find amidst the cracks and hideouts that the barrier offers. These fishes have small protruding mouths that, like tweezers, can reach into the narrowest cracks. Many other fishes have mouths like these, such as the angelfish, the beautiful Zanclus canescens (similar to the lionfish), some file fishes and many others, all predators of small invertebrates.
The crossbow fish, the globefish and the porcupine fish take off pieces of coral, instead, using their strong mouths.
There are also coral fishes that feed on plankton or waste; but most are predators. Large animals are in the open sea, in front of the reef, such as the large green turtle (Chelonia mydas), very many species of sharks and the devilfish (Manta birostris).
Odd invertebrates
This particular ecosystem also includes colourful and quirky invertebrates. Sponges certainly are one of the most important invertebrates of the reef. They feed on food particles carried by the water which are filtered through many tiny pores. The larger holes are instead the so-called “oscula”, from which the animal drains filtered water. The reef sponges exhibit incredibly different shapes, sizes and colours.
There are very many holothurians, also known as “sea cucumbers” because of the shape of their body, with species that can be over one metre long or short and colourful. Starfishes are also brightly coloured in this ecosystem, for instance the garish blue-purple Linkia esatentacolata.

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