It’s common knowledge that coral reefs are the rainforests of the sea—hosting an abundant variety of sea life and crucial habitat for about 25% of all ocean species. It’s true that most people could easily identify a coral reef. But did you know that just like ice cream, corals have two different varieties—soft and hard?
Let’s explore the softer side of corals. If you prefer to learn about hard corals, don’t worry; you can find information on this fact sheet.
- Kingdom: Animalia
- Phylum: Cnidaria
- Class: Anthozoa
- Subclass: Octocorallia
- Order: Alcyonacea
Corals are animals, even though they look like plants and have many of the same characteristics. Soft corals are in the phylum Cnidaria (from the Greek word for “stinging needles”) and the class Anthozoa. Hard corals, anemones and jellyfish are also in the phylum Cnidaria. All Cnidarians have stinging cells called nematocysts(usually around their single opening) and a body symmetry around a single axis point.
Soft corals have soft bodies that can move and flow with the ocean currents. When you look at them, soft corals resemble plants or trees with limbs blowing in the wind whereas hard corals resemble rocks. Soft corals do not have hard calcium carbonate skeletons like hard corals do. As a result, they do not build into reefs. Instead, they grow like trees and have a wood-like core and a soft exterior for protection.
Both soft and hard corals are made up of tiny organisms called polyps. The polyps are soft-bodied, but in hard corals they secrete limestone skeletons for support. In soft corals, the polyps create small, pointy structures called sclerites that help them keep their shape. Large, iconic reefs are formed when many, many polyps come together and build on one another into a colony of polyps that actually acts as one organism. Within their polyps, many corals, both hard and soft, contain microscopic, single-cell algae called zooxanthellae that under photosynthesis produce energy for their host coral. Some coral species that live in deep waters where sunlight doesn’t reach survive without zooxanthellae because they can get their food by filter feeding.
Habitat and Distribution
Soft corals are found all over the world but mostly in tropical or subtropical waters. While soft corals don’t create iconic reefs, they do live on them. Soft corals also grow and thrive in the deep sea. Mature soft corals are attached to the seabed, but their larvae are free-floating and can drift to settle in new areas of the ocean floor. Soft corals exhibit a rainbow of colors—from red, purple, pink, yellow and even bright orange. As for size, this varies. Some species are small and only grow a few inches, while others can grow to several feet in height.
Sea Fans, Sea Feathers and Gorgonian Corals
The order Alcyonacea is also home to sea fans, sea feathers and gorgonian corals. The gorgonian coral creates a hard skeleton made from gorgonin, a unique protein that makes their skeletons different from “true” hard corals. Gorgonian polyps, like other soft coral polyps, have eight tentacles. These tentacles aid in filter feeding by perfectly positioning their fans to catch plankton traveling in water currents.
Soft corals make the perfect home for a variety of ocean animals, including the fun pair of Bargibant’s and Denise’s pygmy seahorses. These seahorses live exclusively on sea fans and are perfectly camouflaged within the coral.
Coral reefs need our help
Coral reefs are being severely damaged by ocean acidification which occurs when the ocean absorbs carbon and becomes acidified. Increasing acidification degrades the physical structure of these reefs and affects all the creatures living on a reef. They are greatly in need of our help!
Ocean Conservancy is at the forefront of the battle against ocean acidification, working with communities, fishermen, governments, businesses and conservation to tackle the root cause of acidification: carbon emissions. We are also advancing local solutions to reduce runoff and supporting research to protect jobs, coastal economies and the way of life of our coastal and island communities.
Will you join donate to Ocean Conservancy to help us implement real solutions to curb carbon emissions and protect our ocean, our reefs and ourselves from the destructive impact of ocean acidification?
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