Seven Reef Bottom Types

Coral reefs are home to all sorts of marine creatures, like corals, fish, eels, octopuses, and so many more. There are also plants like seagrass and seaweed. Because corals build reefs, one of the best indicators of reef health is the abundance of coral. This is what we call Hard Coral Cover or HCC.

But to get an idea about what exactly is happening in the reef, we need to look at what other things can be found in it as well.

In order to do this, you will need to learn how to recognize seven reef bottom types:

How reef images are processed

Even if we condense everything that can be found on the reef into seven types, it would take an extreme amount of time and effort to count every single thing on the reef. Instead, we place ten points on each image and identify which of the seven reef bottom types is under each point.

For example, let’s take a look at this image.

Point A is a live coral or HC, while point B is a white coral or WC. We then write these values down on the appropriate cells in the coral datasheet. We will do this for every point in the image and repeat the process for a total of at least thirty images. But first, you must learn to recognize the seven reef bottom types.

Hard Coral (HC)

The most important organisms on the reef are corals, particularly hard corals. All live hard corals will be classified as HC. Corals can have many different shapes and sizes.

 

Branching corals are shaped like the branches of trees or plants. There are many kinds of branching corals. Some look like solitary bushes, and some can form “meadows” where individual coral colonies are difficult to distinguish.

Massive corals are round or helmet-shaped. They come in many different sizes, from smaller than your fist to underwater hills.

Bubble corals have polyps that are usually extended. This gives them a soft appearance. Some of the polyps look like flowers, while others are elongated and shaped like anchors or beans.

Encrusting corals look like they’re stuck to the reef surface. These corals follow the shape of the reef bottom as they grow and often appear flat.

Foliose corals are vase-shaped or cabbage-shaped. Some look like thin ‘sheets’ that appear as if they are standing up from the reef bottom, while some look like leaves and some overgrow each other.

Unattached corals aren’t attached to the reef bottom like most corals are. These are easy to carry and transfer to other areas. There are usually many of them in one area. They can be round or elongated in shape.

Hard corals also have relatives that form a calcium carbon skeleton as well. These are Heliopora or blue corals and Millepora or fire corals.

Heliopora is brown on the outside with a blue skeleton. It many shapes, like branching, blade-like, or thin standing ‘sheets.’

Millepora is also called the fire coral because of its fiery color and the fiery pain it can inflict when touched. These are often yellow or orange in color and come in various shapes as well.

White Coral (WC)

Healthy, living corals tend to have distinctive colors. But corals which are diseased, stressed, or dead have a white appearance. These are classified as white corals or WC. The entire coral doesn’t have to be white; as long as a part of the coral is white and the point lands on this spot, you can classify it as WC.

There are many reasons why a coral might turn white, so there is an additional set of notes under WC. If a coral has turned white because of warm temperatures underwater, this is called coral bleaching. The note for this is BLEC. Another reason for corals to turn white is because of diseases. The note for this is DIS. Corals may also turn white if they are eaten by Crown-of-thorns starfish. The note for this is COTS.

Seaweed (SW)

All the marine plants and algae which are 3cm or longer are classified as SW. These can have many different sizes and appearances. Some look leafy, while others follow the shape of the reef bottom. They can even look like bubbles.

Other Living Organisms (OTL)

All the marine organisms that live on the reef bottom but aren’t hard corals, plants or algae are classified as OTL or Other Living Organisms. This includes soft corals, sponges, clams, sea anemones, and others.

Algal Assemblage (AA)

AA or Algal Assemblage refers to stable surfaces on the reef where corals can grow. These may have a thin layer of algae doesn’t exceed 3cm, which can look like moss. Even dead corals on which algae has grown can be classified as AA. Surfaces or dead corals that are covered in coralline algae (the pink algae where corals love to grow) are also classified as AA.

Abiotic (AB)

Not all the things found in the reef are alive. AB or Abiotic is the reef bottom type for all non-living things like sand, silt, rocks and rubble or pieces of dead coral.

Tape, Water, Block (TWB)

Sometimes, we see things on the reef that are not found there naturally, such as transect tapes, ropes, trash, or cement blocks. All of these are classified as TWB. TWB is also used for objects which cannot be identified, such as shadows, blurred parts of the image, or parts of the image that are too deep to see clearly.

These seven reef bottom types are all you nee d to remember to gather relevant information on the state of a reef. If you want to see more examples, you can refer to the field guides found here.