Range: Most species diversity in Indo-Pacific region but in tropical and temperate seas around the world

Habitat: Coral reefs, often on soft sand or loose gravel where other coral can't grow

Size: Polyps up to 20 inches (50 cm) in diameter; "Skeleton" can be more than 3 feet (91 cm) long

Diet: Organic material from water and nutrients provided by symbiotic zooxanthellae

Threats: Sea stars, habitat destruction, ocean warming, and more

Lifespan: Ten or more years

Transcript:

Today on Animal Fact Files we’re discussing mushroom corals. When these animals were first discovered, they were believed to be actual mushrooms that had somehow fallen into the ocean and solidified into rocks. Admittedly, these corals look a lot like mushrooms, which is how they got their common name. The ridges on their body's surface give the same impression as the gills in a mushroom cap. These ridges are actually helpful in identifying mushroom coral species. There are about 50 described species of these invertebrates, and the teeth and spines present on their intricate ridges help scientists differentiate them.

Mushroom corals have the most species diversity in Indo-Pacific ocean waters, however they live in tropical and temperate seas around the world. They're sublittoral creatures, meaning they are most often found just off the shore in shallow waters. In fact, they aren't really observed past depths of 130 feet (40 m). These corals are unique because most species spend their adult life detached from the substrate. Many corals are unmoving, spending their days attached to hard substrate, but mushroom corals are free-living and can inhabit the parts of reefs other corals can't, such as soft sandy bottoms and loose gravel. Plus, they in turn act as habitat for all kinds of other animals. Shrimp, worms, crabs, jellyfish, fish, and more call mushroom corals home with some species specifically and only using these corals as a home base.

Coral is most commonly known as a colony forming animal. The coral structure is the "skeleton" in which the polyps live. In the case of mushroom corals, most species are solitary with each "skeleton" housing a single polyp. In this manner, mushroom coral polyps are some of the largest observed in all the living coral species reaching up to 20 inches (50 cm) in diameter! Plus, their "skeleton" can be huge, too. While many have an average six inch (15 cm) diameter, others can reach more than three feet (91 cm) long! They range in color from green to brown with some species sporting more distinct colors such as purple and pink along the tips of their tentacles.

Mushroom corals, like other corals, get their color from algae. When they're young, the coral larvae take in zooxanthellae which then remain inside the polyp for the remainder of its life. These algae provide the polyp nutrients while the polyp gives the algae a safe place to live. The polyps also gather nutrients from the surrounding water. Many species only display their tentacles at night, though some sport these throughout the day, as well. Organic particles in the water are caught by the trailing tentacles and transported to the mouth at the center of the organism. The top portion of a mushroom coral is convex, while the underside is concave, so they rest on their edges when settled in a surface.

Mushroom corals are also unique in their reproductive habits. Even within the same species, different populations in different locations may reproduce in different ways. Some are broadcast spawners with males and females releasing their gametes in a synchronized event. Others brood their eggs. Many species are hermaphroditic and are even able to change sex multiple times in different directions throughout their lifetime. Planktonic coral larvae hatch from eggs and then settle to the seafloor. During this juvenile stage, the mushroom coral is sessile, it doesn't move. However, as it develops its iconic shape, the adult removes itself from the sediment and is able to move about using its tentacles! They can also reproduce asexually by budding and regenerating from broken pieces of the adult.

Predators to mushroom corals include sea stars, such as the crown of thorns sea star. They're also threatened by habitat loss and warming ocean temperatures. Some sources suggest these invertebrates can live more than a decade if in optional living conditions.

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