Hard Coral vs Soft Coral: What’s the Difference?
March 9, 2023
Coral is something that all divers love to see underwater. Coral reefs showcase all the colors of the rainbow, and are where many of our favorite ocean animals call home. We are going to look at the differences between the hard and soft corals that create these incredibly biodiverse ecosystems, and learn how you can recognize them in the water.
What is coral?
Corals are living organisms that are found in many areas of the world, but are usually associated with the warmer waters around the equator of the globe. There are over 6000 species of coral found in the world’s oceans and they come in a proliferation of shapes, colors and structures.
Corals are heavily dependent on a complex symbiotic (mutually beneficial) relationship with photosynthetic algae living within their tissues. These algae remove the waste products of respiration from the coral polyp and use it to produce sugars via photosynthesis. Corals can get over 90% of their necessary nutrition from this incredible relationship. This also shows why most corals are found in the tropics where waters tend to be clear, warm, and have reliable sunlight year round.
Corals are slow growing, with the fastest species reaching just 8-15mm per year. A healthy reef will be thousands of years old, with an overgrowth of multiple layers of coral skeletons. The 2300 km/1430 mile long Great Barrier Reef on Australia’s east coast is the only structure created by living organisms that is visible from space! It is also considered to be one of the natural wonders of the world.
It has been found that coral reefs are relied upon by nearly a quarter of all fish species at some point in their life cycle, this makes coral reefs not just important for fish, but also important to the hundreds of millions of people that get their food from the ocean. Commercially important species such as snapper, grouper, and tunas are all found around coral reefs worldwide. The tourism benefit to countries that have healthy reefs in their waters is also huge with the Great Barrier Reef bringing in over $5.5bn dollars to the Australian economy every year.
Are you ready to get sciency? Next, we are going to look at the differences between hard corals and soft corals.
Hard corals
Hard corals create a solid calcium carbonate skeleton at their base to secure themselves to the reef, they are then totally rigid. It is these solid aragonite skeletons that form the myriad of shapes and structures that we all love to see underwater.
Genera such as the Acropora have eye-catching physical characteristics and typically form a branch or table shape. In the Caribbean species from the Mussidae family exhibit beautiful swirling patterns and if you see a picture you will understand why they have the nickname ‘brain corals’. Some species form less impressive shapes but they are hugely important to forming the bulk of the reef structure itself. The genus Porites is renowned for creating huge mushroom shaped coral bommies which are fun to see on a dive. Whether the coral structure is a branching shape, a table, or a massive coral head with caves and overhangs, hard corals are the true builders in the coral world, manufacturing vital habitat for fish of all ages and species.
Next time you dive, take a peek into all the nooks and crannies that the branching corals create and try to spot a damselfish and butterflyfish that often hide inside. Larger coral heads are sometimes home to groupers, snapper, sweetlips, and shade-loving species like soldierfish and squirrelfish. If you are very lucky you might even see turtles, sharks, and tons of invertebrates like lobsters, crabs, and octopuses also inhabiting the reef made by the hard corals.
Hard coral will typically be found in waters shallower than 40m/130ft but some species can survive deeper. The reduction in available light is a limiting factor for hard corals to grow deep. Some corals live on such shallow reef flats that they are exposed at high tide, leaving them not only out of the water but exposed to the full extent of the tropical sun. They react by producing excessive mucus which not only prevents them from drying out, but acts as a kind of sunscreen to stop them from getting excessive UV damage. Pretty smart, right?
Soft corals
Soft corals can be distinguished from hard corals by their appearance and by their movement in the water. They are also found in a huge range of forms and shapes, from doughy/fleshy shapes to delicate fans and whips.
Some species are much more depth tolerant than their harder cousins; Their large, eight-tentacled polyps feed voraciously in deep water currents. Soft corals are present in larger numbers in temperate or even polar waters because they are not as dependent on algae to produce the bulk of their food.
In the Caribbean sea, fans are the most common type of soft coral that is found, and in the shallows it can form vast colorful fields that gently sway back and forth in the surge. Also found in that region is the Gorgonian sea whips, which are pencil thin and extend off the wall for around 16-20 ft/5-6m and have a beautiful spiral shape. Gorgonians are a rare treat for deep divers to get a picture of. Huge Gorgonian fans can be found in tropical regions around the world, typically on deep drop offs where they will secure themselves to the most exposed point on the reef. This is so they can capture as much planktonic food as possible in the passing current. The Dendronephthya species are another huge favorite for divers, they can be found from the Red Sea and right the way through the Indian and Pacific Oceans. They have fleshy, paler trunks that are covered with brightly coloured polyps. They can be a haven for much sought-after macro life such as the pygmy seahorse.
Certain species of gorgonian have been shown to produce chemicals (diterpenes) that have known antimicrobial properties. These chemicals are being researched for potential human medical advancement, and it has been observed that bottlenose dolphins frequently swim directly through these gorgonian fans to make use of this effect on their skin or abrasions.
Is it too late to help the world’s dying corals? Here is what we think.
Why is it important to take care of coral reefs?
Coral Reefs are under threat from rising sea surface temperatures, ocean acidification and increasing human pressures like tourism and fishing. Coral reefs are second only to the rainforest in terms of biodiversity and the numbers of species that they support. They are also among the most beautiful ecosystems on the planet, so protecting them is so important for future generations to enjoy them too.
Whilst diving it is imperative to maintain excellent buoyancy and avoid making any contact with delicate corals. Signing up for further dive training with courses such as the SSI Perfect Buoyancy, and taking the time to make sure you are correctly weighted are easy and effective ways to make sure you do not accidentally damage the reef you have probably traveled so far to see! Do not stand on the reef at any point, this keeps you from damaging the corals, and also prevents cuts from the reef which can become easily infected.
Another thing you can do to help coral reefs is to use a reef safe sunscreen when you go in the ocean.
Reefs have been shown to respond very well to conservation measures such as a ban on destructive fishing practices (fishing with dynamite), and the outplanting of faster growing species like Acropora. Outplanting coral has been shown to be very effective in kickstarting the regeneration of reefs across the world. With more and more projects like this happening around the world, there is hope for a future with healthy corals.
So show some reef-spect, and help corals to thrive!