Pictures of hard corals in Raja Ampat within the coral triangle

December 2012 

The amount of hard corals, like acropora, which can be found in Raja Ampat is impressive. Their health appears to be excellent, with bright colors determined by a complex relationship with the zooxanthellae algae, producing or masking the pigments.

Acropora coral
Raja Ampat is located in the so-called Coral Triangle, a region characterized by the presence of coral reefs showing the world's larger biodiversity that includes thousands of species ranging from fish, to corals and other invertebrates.
Stylophora coral Smooth cauliflower coral
Hood coral Stylophora pistillata
Photos of corals. Some corals belonging to the genus Stylophora (in particular Stylophora pistillata). The color of the corals is controlled by a complex symbiosis with an algae, as explained below.
Hard coral Coral pigmentation
Coral with zooxanthellae algae

Pictures of acropora corals - why corals have different colors

Many corals, and Acropora in particular, live in symbiosis with algae belonging to the genus Zooxanthella (commonly called zooxanthellae or zoox) that plays an important role on how the color of the coral will be determined. The zooxanthellae live within the coral, where they carry out the activity of photosynthesis, thus using the light and the carbon dioxide to produce sugars and other substances having an high energy value. Such energy is largely transferred to the coral hosting the algae and used for its own growth. In return, the coral provides the algae with its waste products, subsequently reused by the algae for its own business. This closes the circle of symbiosis.

Since the zooxanthellae do not absorb the wavelengths of the solar spectrum corresponding to red, this color is reflected, thus, the greater is the presence of zooxanthellae, the greater will be the brown or reddish color cast of the coral (bottom center photo). Differently, in the case of absence of zooxanthellae, or even in their limited quantity, the pigments naturally present in the coral has the priority over the reds eventually produced by the algae, thus making the corals greenish or bluish, like on the top pictures.

It's important to note that the coral can live in any case even without the zooxanthellae, although the growth will be slower due to the minor availability of nutrients normally supplied by the algae. On the contrary, an excessive presence of zooxanthellae can result in a disadvantage for the coral, as this imbalance may cause that the products generated by the algae are re-used primarily by the algae themselves for their growth, instead of being transferred to the coral. This happens mainly when the zooxanthellae are overfeed by pollution coming from fertilizers for agricultural use, phosphates and nitrates ending into the sea, thus not making necessary to the algae to "ask" for these substances to the coral.

Acropora hyacinthus
Acropora table coral Table coral
Table corals

Pictures of corals (Acropora) living on the reef in Raja Ampat. The growth of the acropora coral is a fairly quick and the "umbrella" that results, can reach 5 meters in diameter. These corals are also known as table corals.
Huge table coral
Photo of coral. A huge table coral having a diameter of several meters.
Zooxanthelle Coral pigmentation
Zooxanthellae algae

More coral photos, showing the presence of zooxanthellae algae in symbiosis (left picture) and the natural pigmentation (above picture) for the possible absence of the Zooxanthella.
Net fire coral
A large cluster of net fire coral, so named for its strong stinging.
Reef Ocean reef
Staghorn coral Staghorn corals
Coral pictures showing a vast reef in Raja Ampat, formed by staghorn corals.
Tubastrea coccinea
Tubastrea coccinea, an hard coral having an unusual shape.
Corals in Indonesia
Pictures of other hard corals.
Hard corals
A red coral.
West Papua corals
Brain corals Brain coral
Pictures of corals characterized by a massive globular shape. The brain coral (bottom-right picture) is part of this group, and is so named because it looks like a brain.
Encrusting coral
Photo of encrusting coral, so called because it grows flat shaped, like a crust over surrounding rocks.
Reef in Indonesia
Massive brain coral Reef in Indonesia
Coral close-up Great star coral
Photos of huge globular-shaped corals and pictures showing some of the textures that you can find on the body of those corals.
Very old coral Montastraea
Montastrea coral
A giant globular coral, probably centuries old, belonging to the genus Montastraea. Also referred to as massive coral, these species are so imposing that they may create a complete ecosystem on top and around them, hosting other corals, sponges and worms.
Tubastrea Sun coral
More hard coral photos. In the pictures above, a coral belonging to the genus Tubastrea.
Reef in West Papua
An hard coral offers a safe refuge to damsel fish.
Montipora coral Montipora
Pictures of leaf-shaped corals, belonging to genus Montipora.
Another type of hard coral.
Ocean reef Indonesian reef
The beautiful reef in Raja Ampat, hosting an incredible quantity and variety of corals.
Reef in Irian Jaya
Irian Jaya reef
More reef photos showing the huge biodiversity that you can find in the Coral Triangle and in Raja Ampat.

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