Coral of the Great Barrier Reef from Port Douglas

Here’s the fact that surprises most visitors: coral is an animal. The Great Barrier Reef,  the largest coral reef ecosystem on Earth,  is built by billions of tiny animals called polyps, living in colonies and laying down limestone one generation on top of the last. When you snorkel over a reef from Port Douglas, you’re floating above a living structure that these animals have been constructing for thousands of years.

This guide explains what coral actually is, the main types you’ll see, why coral sometimes turns white, and how to enjoy the reef without harming it.

Scientific classification

Corals are marine invertebrate animals in the phylum Cnidaria, the same group as jellyfish and sea anemones. “Hard” reef-building corals secrete a calcium-carbonate skeleton; “soft” corals do not. Below are representative genera a Port Douglas visitor may see, with classification and AphiaIDs from the World Register of Marine Species (WoRMS).

Higher classification: Kingdom Animalia > Phylum Cnidaria > Class Anthozoa. Hard corals belong to the order Scleractinia; soft corals to the order Alcyonacea (octocorals).

Is coral a plant or an animal?

An animal. A coral colony is made of thousands of genetically identical polyps,  small, soft-bodied invertebrates related to anemones. Its plant-like appearance and colour come from something living inside it: microscopic algae called zooxanthellae that live in the coral’s tissue. The algae photosynthesise and provide up to 90 per cent of the energy reef-building corals need to grow, while the coral gives the algae a safe, sunlit home. This partnership is the engine of the whole reef, and it’s also why coral is so sensitive to heat (see bleaching, below).

Hard coral and soft coral

• Hard (stony) corals build a skeleton of calcium carbonate,  limestone,  by drawing calcium and carbonate from seawater. Over time these skeletons form the solid framework of the reef itself, providing food and shelter for countless other animals. Staghorn and plate corals (Acropora) grow fast in branching or table shapes; boulder corals (Porites) grow slowly into long-lived domes; brain corals form rounded heads with maze-like ridges.
• Soft corals have no stony skeleton. They’re often the most colourful things on the reef, swaying with the current in leathery, tree- or finger-like shapes, and tend to favour spots sheltered from waves.

How many kinds of coral are on the Great Barrier Reef?

A lot, though the exact count depends on which authority you read and how they define “coral.” The Reef Authority records around 450 types of hard coral, and depending on how corals are classified, some scientific counts run higher still. Either way, the Great Barrier Reef has one of the richest coral communities on the planet, plus many hundreds of species of soft coral.

Where you’ll see coral around Port Douglas

Port Douglas is a gateway to both the outer and inner reef. Day trips reach the outer-shelf ribbon reefs,  the Agincourt Reefs and Opal Reef sit in what the Reef Authority calls the “Offshore Port Douglas Sector”, while the inshore Low Isles, a coral cay off Port Douglas, offer a gentler, shallower reef. The particular corals a given trip shows, and their condition on the day, vary with the site and the season, so we describe what the region holds rather than promising a specific view.

Why does coral bleach?

Corals live within a narrow temperature range, and even about 1°C above the normal summer maximum causes heat stress. Under stress, the coral expels its zooxanthellae,  and because those algae provide the colour, the coral’s tissue turns transparent and the white skeleton shows through. That’s “bleaching.” Importantly, a bleached coral is stressed, not automatically dead: reefs can recover if the heat stress eases in time.

Reef condition changes from year to year. As of the AIMS Annual Summary Report of Coral Reef Condition 2025/26, hard-coral cover across the Reef’s three regions had increased slightly or held steady compared with the previous year, described by AIMS as the start of recovery following the 2024 mass-bleaching event, helped by cooler monsoon conditions. The picture remains variable reef-to-reef and vulnerable to future heat stress.

Threats to the reef

• Climate change and marine heatwaves,  the Reef Authority describes this as the greatest threat to the Reef, and the driver of mass bleaching.
• Crown-of-thorns starfish,  a coral-eating starfish whose outbreaks were responsible for an estimated 42% of the Reef’s coral-cover loss between 1985 and 2012; the Reef Authority runs a dedicated control program.
• Water quality and runoff, and cyclones,  cumulative pressures that slow recovery.

How to protect the coral

The Reef Authority’s responsible-reef practices are simple and they matter:

• Don’t touch or stand on coral. Get your buoyancy sorted over sand before you approach the reef, and keep your fins clear.
• Take nothing. Collecting coral, even dead coral,  is prohibited in the Marine Park without a permit.
• Stay off the reef and follow your guide’s briefing and the zoning rules.

Coral and the Port Douglas reef experience

Coral is the habitat that everything else depends on,  the reef’s fish, giant clams, sea turtles and reef sharks all live on or around it. To see it, our snorkelling overview explains how most visitors experience the reef, and the Mackay Coral Cay and Opal Reef guides describe specific reef environments. To choose a trip, see Low Isles vs Outer Reef and Which Great Barrier Reef tour is right for you?, or browse Great Barrier Reef tours from Port Douglas. Return to the Marine Life of the Great Barrier Reef hub any time.

Frequently asked questions

Is coral a plant or an animal?
An animal,  a colony of tiny polyps (relatives of jellyfish and anemones). Its colour comes from symbiotic algae living inside it, not from the coral being a plant.

What types of coral are on the Great Barrier Reef?
Hard (stony) corals that build the reef’s limestone skeleton, staghorn and plate (Acropora), boulder (Porites), brain corals, and soft corals with no stony skeleton, such as Sarcophyton.

How many coral species are there?
It depends on the source: the Reef Authority records around 450 types of hard coral, and some scientific counts run higher depending on how corals are classified,  plus many hundreds of soft corals.

Why does coral bleach?
Heat stress,  water even about 1°C above the summer maximum, breaks the coral–algae partnership. The coral expels its algae and turns white. Bleached coral isn’t automatically dead and can recover if the heat eases.

Will I see healthy coral from Port Douglas?
Port Douglas trips reach outer-shelf reefs (Agincourt, Opal) and the inshore Low Isles. AIMS reported the northern Reef in early recovery in its 2025/26 report, though condition varies by reef and year,  so we describe the region honestly rather than promising a particular view.

How do I protect the coral?
Don’t touch or stand on coral, keep good buoyancy, take nothing (collecting coral is prohibited without a permit), and follow your guide and the zoning rules.

Sources & credits

Coral biology, bleaching and reef condition: Australian Institute of Marine Science (AIMS), including the Annual Summary Report of Coral Reef Condition 2025/26. Species numbers, threats, protected-area rules and responsible-viewing guidance: Great Barrier Reef Marine Park Authority (Reef Authority). Taxonomy and AphiaIDs: World Register of Marine Species (WoRMS). Reef-condition figures reflect the cited report year and change annually. This page is educational and does not guarantee reef conditions or wildlife sightings.

Local reef knowledge & expert contribution

Are you a coral scientist, reef ecologist or Master Reef Guide working the reefs off Port Douglas, or involved in coral restoration? We welcome expert review, imagery and up-to-date reef-condition insight. Contributors add expertise and credibility and gain mutual visibility, but never buy rankings, placement or recommendations,  our guidance always reflects what genuinely serves the visitor and the reef.