Coral encyclopaedia

28 Red Sea corals: hard and soft corals and anemones — symbiosis, bleaching science, and conservation

Source: Corals of the WorldTaxonomy: WoRMS / CoralBaseData: NOAA Coral Reef Watch

Coral is an animal, not a rock: each piece is a colony of thousands of polyps (1–3 mm) that secrete limestone. Zooxanthellae live with them in a complex mutualism. Dead coral is not “old stone” — it was breathing hours or years ago.

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Family Acroporidae

The genus Acropora is the largest coral genus on Earth — comprising over 150 species. It is called “coral skeletons” because it builds the main structures of the reef. It grows at the fastest rates among stone corals (3–15 cm/year) but is most fragile to bleaching and prickly crowns.

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Jess · CC BY-NC 4.0

Florida Staghorn Coral

Acropora florida

NT — Near ThreatenedHard coral

Depth

1–25 m

Growth rate

5–15 cm/year

Range

Red Sea, Indian Ocean, western Pacific

Family

Acroporidae

One of the most common corals on shallow Red Sea reefs. Tapered finger-like branches rise vertically and shelter many small fishes and crustaceans. A frequent target of Cliona boring sponges and crown-of-thorns starfish.

Scientific notes (4)▼

1.Zooxanthellae — symbiotic algae in its tissues — supply about 90% of its food through photosynthesis
2.Bleaching is a heat signal — it expels zooxanthellae when temperature stays above 31°C for weeks
3.It is used in coral-gardening projects worldwide because it grows quickly
4.In major bleaching years (such as 1998 and 2016) 60–80% died in some areas

GBIF: 5184677

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Robin White · CC BY-NC 4.0

Table Coral

Acropora cytherea

NT — Near ThreatenedHard coral

Depth

5–40 m

Growth rate

4–10 cm/year

Range

Widespread in the Indian Ocean, Pacific, and Red Sea

Family

Acroporidae

It forms a flat horizontal table up to two metres across. Branches face the light; fishes shelter beneath. Large tables may be 20–50 years old.

Scientific notes (4)▼

1.The table shape evolved to capture more sunlight in deeper water
2.A table colony can snap with a light touch — it looks sturdy but is brittle
3.They shelter dozens of small fish and crustacean species underneath
4.The largest recorded tables exceed 3 m across — often more than 50 years old

GBIF: 5184592

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Sol Yoder · CC BY-NC 4.0

Pharaoh Coral

Acropora pharaonis

VU — VulnerableHard coral

Depth

2–20 m

Growth rate

4–8 cm/year

Range

Endemic to the Red Sea and Arabian Gulf

Family

Acroporidae

A Red Sea endemic named for its discovery there. Fine interlocking branches form dense coral thickets of high diversity. Listed as vulnerable from bleaching and collection pressure.

Scientific notes (4)▼

1.A Red Sea endemic — it is not found in any other sea
2.It is a priority species in Saudi and Jordanian conservation programmes
3.Large colonies grow at 5–15 m on some of the finest reef slopes
4.Listed VU because of its small range plus rising heat stress

GBIF: 5184568

Family Merulinidae / Lobophylliidae (former Faviidae)

What was known as the Faviidae family was newly reclassified into several families. Giant mass corals that live include hundreds or even thousands of years — a historical record of the climate etched into their structures.

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Olivia Bañez · CC BY-NC 4.0

Maze Brain Coral

Platygyra daedalea

LC — Least ConcernHard coral

Depth

1–20 m

Growth rate

0.5–1.5 cm/year

Range

Red Sea, Indian Ocean, western Pacific

Family

Merulinidae

It resembles a human brain in maze-like folds from polyps that stay joined. Growth is slow but colonies live for centuries and take heat better than Acropora.

Scientific notes (4)▼

1.The maze surface area boosts zooxanthellae and photosynthetic efficiency
2.Some live more than 900 years — skeletons read like tree rings
3.More bleaching-resistant than Acropora — it can survive short heat events
4.It feeds at night when polyps emerge from the limestone to catch plankton

GBIF: 5184733

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iNaturalist · CC BY 4.0

Star Coral

Favia stelligera

LC — Least ConcernHard coral

Depth

1–30 m

Growth rate

0.5–2 cm/year

Range

Widespread in the Red Sea, Indian Ocean, and Pacific

Family

Merulinidae

Dome or massive colonies covered in regular stars, each a polyp. A major reef-builder that forms a hard base for other animals.

Scientific notes (4)▼

1.Each star on the surface is a polyp with its own mouth and tentacles
2.It spawns sexually in a synchronised night-time mass release of gametes
3.More tolerant of pollution and turbid water than delicate branching corals
4.Used as a water-quality indicator in environmental monitoring

GBIF: 2260124

Family Poritidae

The most resilient and longest-living corals. A single colony can live for a thousand years or more. They form massive, solid masses that are the backbone of many reefs.

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iNaturalist · CC BY-NC 4.0

Massive Porites Coral

Porites lutea

LC — Least ConcernHard coral

Depth

0–25 m

Growth rate

0.8–1.2 cm/year

Range

Widespread across the Indian Ocean, Pacific, and Red Sea

Family

Poritidae

Among Earth’s longest-lived animals — huge masses reach 500–1000 years. Dull brown-yellow with a grainy surface. They handle sharp environmental swings and bleach less than most.

Scientific notes (4)▼

1.Colony age can be read by X-ray, like annual tree rings
2.Old masses hold a centuries-long record of climate, storms, and bleaching
3.Cliona sponges bore tiny holes in the surface — slow but lasting damage
4.Less heat-sensitive than many corals — a classic marker of old reef

GBIF: 5184758

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Tom Heijnen · CC BY-NC 4.0

Column Porites

Porites columnaris

LC — Least ConcernHard coral

Depth

3–30 m

Growth rate

1–2 cm/year

Range

Red Sea, western Indian Ocean

Family

Poritidae

Clear columnar growth, sometimes a metre high, forming underwater stone thickets that shelter small reef fishes.

Scientific notes (3)▼

1.Tall columns mark low-current sites where corals compete upward for light
2.It bleaches in sequence — outer columns first, inner ones more sheltered
3.Dead old surfaces can be colonised by other coral species

GBIF: 5720616

Family Pocilloporidae

Tree and branch corals are relatively fast-growing, preparing shallow reef structures and hosting many larvae and small organisms.

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calebbergman · CC BY-NC 4.0

Cauliflower Coral

Pocillopora damicornis

NT — Near ThreatenedHard coral

Depth

0–25 m

Growth rate

2–8 cm/year

Range

Tropical worldwide — common in the Red Sea

Family

Pocilloporidae

Dense cauliflower-like branches; an early coloniser of hard surfaces. Bleaching-sensitive but it recolonises relatively fast.

Scientific notes (3)▼

1.Often used in marine experiments on spawning and bleaching
2.Its larvae settle readily and help reconnect reef patches
3.It can take harsher conditions than Acropora, but it is not immune

GBIF: 2870930

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ewoutknoester · CC BY-SA 4.0

Smooth Cauliflower Coral

Stylophora pistillata

NT — Near ThreatenedHard coral

Depth

0–40 m

Growth rate

2–6 cm/year

Range

Indian Ocean, Pacific, and Red Sea

Family

Pocilloporidae

Tapered barley-like branches in pink or pale brown. Among the commonest corals on shallow reefs.

Scientific notes (3)▼

1.It tolerates a wider temperature range than some Acropora species
2.Dense colonies shelter juvenile fishes
3.It is tracked in reef-health reports

GBIF: 2870939

Subclass Octocorallia

Radically different from stone corals — they produce not hard lime structure but flexible internal structures. Adds bright colors and an aesthetic elasticity to the reef. It has 8 threads on each polyp (octet) for 6 or its multiples in stone.

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erinwoodward · CC BY-NC 4.0

Carnation Coral

Dendronephthya sp.

NE — Not EvaluatedSoft coral

Depth

5–60 m

Growth rate

Variable

Range

Red Sea, Indian Ocean, and Pacific

Family

Nephtheidae

Among the brightest reef animals — swollen trees in red, orange, purple, and pink. They inflate in current and shrink without it. No zooxanthellae; they filter plankton. They often cloak reef walls in vivid colonies.

Scientific notes (4)▼

1.They inflate and deflate with current — swell while feeding, shrink in slack water
2.They have no zooxanthellae — all food comes from filtering plankton
3.Bright colours come from pigments and defensive sclerites, not photosynthesis
4.Among the hardest aquarium species — they need strong, constant flow

GBIF: 2263423

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Wikimedia Commons · CC BY-SA 3.0

Sea Fan / Gorgonian

Subergorgia mollis

LC — Least ConcernSoft coral

Depth

10–80 m

Growth rate

Variable

Range

Red Sea, Indian Ocean, and parts of the Pacific

Family

Subergorgiidae

A fan or mesh held across the current to filter plankton. A flexible axial skeleton is covered in coloured tissue. Colonies live for decades and host specialised fishes and crustaceans.

Scientific notes (4)▼

1.A single network can span hundreds of square metres on reef walls
2.They host pygmy seahorses that camouflage in the branches
3.The flexible skeleton rides strong current — it sways instead of snapping
4.They grow slowly (2–3 cm/year) and take decades to reach full size

GBIF: 2262894

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Wikimedia Commons · CC BY-SA 3.0

Leather Coral

Sarcophyton trocheliophorum

LC — Least ConcernSoft coral

Depth

1–20 m

Growth rate

Variable

Range

Widespread in the Red Sea, Indian Ocean, and western Pacific

Family

Alcyoniidae

Mushroom or cap-shaped: a smooth disc with short polyps. Colour runs brown to green to white with zooxanthellae density. Chemicals slow neighbouring hard coral — quiet competition.

Scientific notes (4)▼

1.It secretes toxic terpenes that slow neighbouring hard coral and block settlement
2.It can drop polyps and resettle them — a defence and a way to spread
3.One of the easiest reef animals to culture — common in home coral tanks
4.Sarcophine compounds from it are studied for medical anti-cancer research

GBIF: 5185182

Order Actiniaria

Animal organisms despite their plant appearance — belonging to the same group of corals (Cnidaria). Their capillary strands numb the passing fish. But at the same time, it is a safe home for clownfish in an amazing symbiotic relationship.

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momaz · CC BY-NC 4.0

Bubble-tip Anemone

Entacmaea quadricolor

NE — Not Evaluated

Depth

1–40 m

Growth rate

Variable

Range

Wide range in the Red Sea, Indian Ocean, and western Pacific

Family

Actiniidae

The preferred host of Red Sea clownfish Amphiprion bicinctus. Balloon-tipped tentacles are the giveaway. Colour shifts purple, brown, or green with site and zooxanthellae.

Scientific notes (4)▼

1.Tentacles hold nematocysts that stun passing fishes at once
2.Clownfish mucus protects them from the sting — the mechanism is still not fully known
3.It can crawl centimetres a day toward better light or a better holdfast
4.One anemone can host several clownfish pairs in side groups

GBIF: 4339208

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David Witherall · CC BY 4.0

Magnificent Sea Anemone

Heteractis magnifica

NE — Not Evaluated

Depth

1–20 m

Growth rate

Variable

Range

Red Sea, Indian Ocean, and western Pacific

Family

Stichodactylidae

One of the world’s largest anemones — a 50 cm foot disc and tentacles to 10 cm. White or purple with coloured spots. The “Rita” anemone of Finding Nemo. It can host several clownfish species.

Scientific notes (4)▼

1.They can live more than 100 years — among the longest-lived of these animals
2.They release holothurin-like toxins to deter predators
3.Prey is digested in the internal gastrovascular cavity
4.The partnership with Amphiprion goes back about 50 million years in the fossil record

GBIF: 5184183

Coral Bleaching: Science & Solutions

Coral bleaching is not an instant death — it is a distress call. Corals expel their symbiotic algae (zoxanthylae) in response to thermal or chemical stress, turning white. If the stress is gone within weeks, the coral returns. But if he continues, he dies of starvation.

Coral Bleaching Phenomenon

Symbiodiniaceae expulsion

NE — Not EvaluatedHard coral

Depth

all depths

Growth rate

Variable

Range

Worldwide — major events: 1998, 2010, 2015–2016, 2022–2023

Family

Marine ecology

Zooxanthellae (Symbiodinium and allies) are single-celled algae in coral tissue supplying 70–90% of its food. Above a heat threshold (often 1°C over the usual maximum) they harm the coral and are expelled. The white skeleton is limestone with no living tissue.

Scientific notes (5)▼

1.2016 saw the worst documented bleaching — more than 50% of Australia’s Great Barrier Reef bleached
2.The Red Sea resists bleaching better than most seas after millennia of heat selection
3.Coral-gardening projects try to restore reefs by planting fragments of resistant species
4.NOAA issues Coral Bleaching Watch alerts when sea temperature exceeds the threshold
5.Diver awareness: do not touch coral, stand on it, or dump sand over it

Coral safety rules for divers

⚠Do not touch any coral — one fingerprint can kill years of growth

⚠لا تقف على الشعاب — up to لو بدت حجارة ميتة

⚠Do not stir sand or silt over reefs — they smother underneath

⚠Do not use chemical sunscreen — oxybenzone is toxic to coral

⚠ابقَ مسافة 1.5 m على الأقل فوق القmm المرجانية

⚠Report bleaching to the dive centre or the relevant environmental authority

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