Reef Guide
Meet every inhabitant of the ReefHub reef — stats, biology, and surprising facts for all 57 species, corals, and visitors.
Clownfish
Famous for their bold orange and white stripes, clownfish live in a symbiotic relationship with sea anemones. The anemone's stinging tentacles protect them while the clownfish chases away predators.
All clownfish are born male. The dominant fish in a group can change sex to become female.
Blue Tang
The blue tang is a laterally compressed disc-shaped fish found across Indo-Pacific reefs. It grazes on algae, keeping reef surfaces clean and helping corals grow.
Their name "surgeonfish" comes from a razor-sharp spine near the tail base that can slice like a scalpel.
Yellow Tang
The yellow tang is one of the most recognisable reef fish, its vivid sulphur-yellow disc body and tall fins making it instantly identifiable. Native to the Pacific Ocean, it grazes constantly on algae and helps keep reef surfaces clear.
Like all surgeonfish, yellow tangs carry a razor-sharp retractable scalpel spine on each side of the tail base — used for defence and territorial disputes.
Angelfish
Marine angelfish are among the most visually striking reef inhabitants, displaying vivid color patterns that signal species identity and dominance. They feed on sponges, algae, and small invertebrates.
Juvenile angelfish often look completely different from adults — some species undergo dramatic color transformations as they mature.
Wrasse
Wrasses are one of the most diverse fish families on coral reefs. Many species operate "cleaning stations" where they remove parasites and dead tissue from larger fish that queue up to be serviced.
Some wrasses can change from female to male mid-life, altering both color and behavior almost overnight.
Damselfish
Despite their small size, damselfish are fiercely territorial and will charge at fish many times their size to defend their patch of algae. They actively "farm" algae by killing and removing competing corals.
A damselfish will aggressively defend its algae garden even from scuba divers, repeatedly nipping at fingers and masks.
Surgeonfish
Surgeonfish are vital reef grazers that control algae growth, allowing corals to thrive. They often travel in large schools that sweep across the reef like a living lawnmower.
The scalpel-sharp spine at the base of the tail can be raised like a switchblade when the fish feels threatened.
Parrotfish
Parrotfish use their fused beak-like teeth to scrape algae off coral rock. The indigestible coral is ground up and excreted as white sand — a single large parrotfish produces over 90 kg of sand per year.
Some parrotfish secrete a mucus cocoon around themselves each night as a sleeping bag — possibly to mask their scent from predators.
Goby
Gobies are among the smallest vertebrates on earth. Many species live in symbiosis with burrowing shrimp — the near-blind shrimp digs and maintains the burrow while the sharp-eyed goby keeps watch, twitching its tail to warn of danger.
The dwarf goby (Eviota sigillata) lives for only 59 days — the shortest lifespan of any known vertebrate.
Butterflyfish
Butterflyfish are among the most recognizable reef fish, their disc-shaped bodies adorned with intricate patterns. Many species are monogamous and patrol fixed territories as mated pairs.
Many butterflyfish have a dark spot near their tail that resembles an eye — predators attack the wrong end, giving the fish time to escape.
Moorish Idol
The Moorish idol is instantly recognizable by its dramatic elongated dorsal fin. Unlike its lookalike the butterflyfish, the Moorish idol is notoriously difficult to keep in captivity due to its specialized diet.
The species' name comes from the Moors of Africa, who believed the fish to be a bringer of happiness.
Chromis
Chromis are small, schooling fish that form shimmering clouds above coral heads. They feed on zooplankton drifting in the current and dart back to the coral at the first sign of a predator.
Male chromis fans and guards the nest until the eggs hatch — one of the few reef fish species with dedicated parental care.
Pufferfish
Pufferfish defend themselves by rapidly inflating their elastic stomach with water, becoming a spiky ball up to three times their normal size. Their organs contain tetrodotoxin, one of the most potent natural toxins known.
Despite being extremely toxic, pufferfish are a prized delicacy in Japan called fugu — only specially licensed chefs are allowed to prepare it.
Filefish
Filefish are named for their rough, sandpaper-like skin. They have a unique dorsal spine that locks upright as a defense mechanism, making them difficult to swallow. Many species can change color to blend in with their surroundings.
Some filefish species have been observed eating the polyps of certain coral species while leaving others untouched.
Anthias
Anthias are vibrantly colored fish that form large haremic schools around coral outcroppings. The brilliant pink or orange coloring of males signals their dominance, while females are generally more subdued.
In a school of anthias, if the dominant male disappears, the largest female will change sex to become the new male within a few weeks.
Blenny
Blennies are cheeky little fish that perch on exposed coral and rock, peering at the world with comically large eyes. They scrape algae off surfaces with comb-like teeth, and often retreat into small crevices when threatened.
The fang blenny injects a venom that contains opioid compounds, causing predators to release it unharmed, dazed but not in pain.
Goatfish
Goatfish are easily recognized by two long chin barbels — sensory organs they use to probe sand and rubble for hidden worms, crustaceans, and molluscs. They can rapidly change color from white to red.
Goatfish are sometimes followed by a "gang" of opportunistic fish that dart in to steal prey items disturbed by the goatfish's rooting behavior.
Lionfish
Lionfish are ambush predators armed with venomous dorsal spines. Native to the Indo-Pacific, they have become an invasive crisis in the Atlantic, where they lack natural predators and devastate reef fish populations.
A single lionfish can consume up to 30 times its stomach volume in prey. In invaded areas, they can reduce juvenile reef fish populations by up to 79% within five weeks.
Grouper
Groupers are large, powerful ambush predators that lurk near coral heads and rocky outcroppings. They are protogynous hermaphrodites, beginning life as females and later transitioning to males.
Groupers have been observed cooperating with moray eels to hunt — the eel flushes prey from crevices while the grouper catches anything that escapes into open water.
Giant Trevally
Giant trevally are apex reef predators that can reach over 80 kg. They hunt in coordinated groups, herding schools of smaller fish toward the surface or against reef walls. Their silver flash is a common sight in clear tropical waters.
Giant trevally are known to leap out of the water to catch birds — particularly seabirds flying low over the surface.
Red Snapper
Snappers are commercially important reef predators that hunt at night, feeding on fish, shrimp, and cephalopods. During the day they school in large aggregations, sometimes numbering in the thousands.
Snappers can live for over 50 years — the age of a red snapper can be determined by counting growth rings in a tiny bone called an otolith, similar to counting tree rings.
Scorpionfish
Scorpionfish are masters of camouflage, blending perfectly with coral rubble and rocky substrate. They sit motionless for hours, then lunge with explosive speed to swallow prey whole. Their dorsal spines deliver potent venom.
The stonefish, a close relative, is considered the most venomous fish in the world. Its venom can cause intense pain, heart failure, and even death.
Trumpetfish
Trumpetfish have an elongated body they use to "shadow" larger fish, drifting alongside them until they're close enough to ambush small prey. They can also hover vertically among sea rods and gorgonians, invisible to passing fish.
Trumpetfish are remarkably flexible shape-shifters when hunting — they can pivot 180° in under 6 milliseconds to engulf prey.
Reef Shark
Reef sharks are the apex predators of coral reef ecosystems. Their presence is essential to reef health — by controlling populations of mid-level predators, they maintain balance throughout the food web.
Sharks have electroreceptors called ampullae of Lorenzini that can detect the faint electrical fields produced by prey's muscle contractions, even through sand.
Octopus
Octopuses are the most intelligent of all invertebrates, capable of using tools, solving puzzles, and navigating mazes. They have three hearts, blue blood, and can change color and texture in milliseconds.
An octopus has no skeleton, allowing it to squeeze through any opening larger than its beak — the only rigid part of its body.
Spiny Lobster
Spiny lobsters lack the large claws of their cold-water cousins but are covered in sharp spines for defense. They are nocturnal scavengers that emerge after dark to forage for detritus, sea urchins, and molluscs.
During autumn migrations, hundreds of spiny lobsters walk in single file across the ocean floor for days, each touching the one in front, navigating by Earth's magnetic field.
Reef Crab
Reef crabs are opportunistic scavengers and predators found in every niche of the coral reef — under rubble, in coral crevices, and on sandy flats. They play an essential role in recycling organic matter on the reef floor.
Crabs navigate using celestial cues, polarized light, and chemical gradients. Some reef crabs decorate their shells with bits of sponge and algae as both camouflage and chemical defense.
Jellyfish
Jellyfish are among the oldest animals on Earth, having drifted through oceans for over 500 million years before dinosaurs existed. They have no brain, heart, or bones — yet they are highly effective predators, paralyzing prey with stinging cells called nematocysts.
The immortal jellyfish (Turritopsis dohrnii) can revert back to its juvenile polyp stage after reaching adulthood — the only known biologically immortal animal.
Seahorse
Seahorses anchor to coral and seagrass with their prehensile tails, drifting very little. They are ambush predators, snapping up tiny crustaceans by suddenly expanding their snout. Mated pairs perform daily greeting dances.
Seahorses are the only species on Earth where the male becomes pregnant — females deposit eggs into a pouch on the male's abdomen, and he gives birth to up to 2,000 young.
Giant Clam
Giant clams are the largest living bivalve molluscs, capable of living for over 100 years. They harbor photosynthetic algae (zooxanthellae) in their mantle tissue, which provide nutrition through photosynthesis — similar to how corals feed.
The vivid blue and green colors of a giant clam's mantle come from iridophores — cells that reflect and scatter light to optimize photosynthesis for their symbiotic algae.
Sea Turtle
Sea turtles are ancient mariners that have navigated Earth's oceans for over 100 million years. They graze on seagrass and algae, keeping seagrass beds healthy and providing habitat for small marine life. They travel thousands of miles to return to the beach where they were born.
Sea turtles navigate using the Earth's magnetic field. Females remember the exact magnetic signature of their birth beach and return to nest there decades later.
Fan Coral
Fan corals grow in a single flat plane perpendicular to prevailing currents, maximizing exposure to drifting plankton. Their lacy, net-like skeleton provides shelter for tiny fish, seahorses, and crustaceans.
Pygmy seahorses are so perfectly camouflaged against specific fan coral species that they were only discovered in 1969, after a researcher brought a fan coral to his lab and found a seahorse living on it.
Staghorn Coral
One of the most important reef-building corals in the Caribbean, staghorn coral creates complex three-dimensional habitat for hundreds of reef species. It is now critically endangered due to warming oceans and disease.
Staghorn coral can grow up to 10 cm per year — unusually fast for a coral — by asexually budding new polyps from existing ones, effectively cloning itself as it expands.
Table Coral
Table corals (Acropora hyacinthus) grow into massive flat platforms that provide refuge for dozens of fish species at once. These structures can span over 3 metres and represent decades of uninterrupted growth.
The flat plate shape maximises light exposure for the zooxanthellae algae living inside the coral's tissue, which supply up to 90% of its energy needs through photosynthesis.
Bubble Coral
Bubble coral (Plerogyra sinuosa) inflates transparent grape-like vesicles during the day to maximise light absorption. At night the bubbles retract and long sweeper tentacles emerge to sting any neighboring corals within reach.
Bubble coral sweeper tentacles can extend up to 15 cm beyond its skeleton — far enough to sting and kill competing corals growing nearby, clearing space around the colony.
Sea Anemone
Sea anemones are close cousins of corals and jellyfish. They anchor to substrate and extend stinging tentacles to catch small fish and crustaceans. Some species can live for over a century without aging in the traditional sense.
Clownfish are immune to anemone stings due to a protective mucus coating. The two species have a deeply mutualistic bond — the fish keeps the anemone clean and chases off predators, while the anemone provides shelter.
Seaweed & Algae
Macroalgae are essential primary producers on reef systems, converting sunlight into biomass consumed by parrotfish, tangs, and sea urchins. They form the base of the reef food web and must be kept in check by herbivores.
When reef herbivores are removed through overfishing, algae can overtake and smother corals within weeks. A single large parrotfish can keep over 10 m² of reef algae-free through constant grazing.
Torch Coral
Torch corals (Euphyllia glabrescens) are favored by reef aquarists for their flowing, tentacles tipped with contrasting color. In the wild they are highly territorial — their long tentacles sting any coral that comes within range.
Torch coral polyps move and wave with the current almost like soft tissue, yet beneath the flowing tentacles lies a hard calcium carbonate skeleton that has been slowly built up over decades.
Whip Coral
Whip corals grow as a single elongated unbranching strand, swaying gracefully in the current to filter plankton. They often host tiny associate species — wire coral gobies and shrimp — that match the whip's color exactly.
Some whip corals grow less than 1 cm per year, meaning a 2-metre specimen could be over 200 years old — a silent witness to centuries of reef history.
Pillar Coral
Pillar coral (Dendrogyra cylindricus) is one of the few coral species whose polyps extend during the day rather than at night, giving the columns a fuzzy, textured appearance. It is critically endangered and found only in the Caribbean.
Surveys in the Florida Keys found pillar coral populations declined by over 90% between 1990 and 2016, primarily due to stony coral tissue loss disease — one of the most devastating coral diseases ever recorded.
Plating Coral
Plating corals grow in stacked horizontal shelves, each plate optimized to harvest light at different angles. The layered architecture creates dense micro-habitats where juvenile fish shelter from predators between the shelves.
The spacing between plating coral layers is precisely calibrated — each shelf avoids shading the layer below, maximizing total light collection across the entire colony at once.
Columnar Coral
Columnar corals grow as clusters of upright cylinders, creating a distinctive organ-pipe appearance. The spaces between columns shelter gobies, blennies, and countless invertebrates that use the structure as permanent homes.
Brain coral — a columnar cousin — grows just a few millimetres per year. The largest known specimens are over 500 years old, predating modern nations.
Gorgonian Sea Fan
Gorgonian sea fans are colonial octocorals that orient perpendicular to prevailing currents, presenting their branching network to filter passing plankton. Their flexible skeletal axis contains a protein called gorgonin.
Compounds isolated from Caribbean sea fans led to the development of Pseudopterosin — a patented anti-inflammatory used in cosmetics. Scientists continue to investigate gorgonians as a source of novel pharmaceuticals.
Brain Coral
Brain corals are massive dome-shaped corals whose surface is covered with sinuous valley-and-ridge patterns resembling the folds of a human brain. They are among the slowest-growing corals, adding only 0.3–1 cm per year, but can live for 900+ years.
The maze-like ridges on a brain coral's surface are rows of polyps all fused together. Each groove is a shared mouth slot — hundreds of polyps eating side-by-side in a continuous chain.
Elkhorn Coral
Elkhorn coral (Acropora palmata) builds large, flattened antler-shaped branches that can grow over 10 cm per year — one of the fastest rates of any reef coral. Its dense thickets once dominated shallow Caribbean reefs and provided critical wave-buffering for coastlines.
Elkhorn coral was so abundant before 1980 that early Caribbean divers described swimming through forests of it. Today it has lost over 97% of its historical coverage and is listed as critically endangered.
Mushroom Coral
Mushroom corals (Fungiidae) are unusual in that most species are free-living as adults — they are not attached to the reef. A single large polyp forms the entire disc-shaped colony. They can slowly move across the seafloor and right themselves if flipped over.
Juvenile mushroom corals start life attached to a stalk. At some point the disc breaks free, leaving the stalk behind. That stalk then regenerates into a new disc — one coral can clone itself this way repeatedly.
Fire Coral
Fire coral (Millepora) is not a true coral but a hydrozoan — more closely related to jellyfish than to stony corals. It grows as flat upright blades or branching columns and delivers a painful sting on contact, causing burning, welts, and itching that can last days.
Fire coral is one of the most frequent causes of injury for reef divers and snorkellers. The sting comes from thousands of microscopic nematocysts covering the surface — even brushing it lightly with skin or a wetsuit triggers the reaction.
Hammer Coral
Hammer coral (Euphyllia ancora) is named for its distinctive T-shaped or anchor-shaped tentacle tips that wave gently in the current. A close relative of torch coral, it is highly territorial and will sting neighboring corals with potent sweeper tentacles at night.
Hammer coral tentacles glow under UV light — a trait likely used for communication between polyps and possibly to attract prey. Under a diver's UV torch the colony shimmers with eerie blue-green luminescence.
Organ Pipe Coral
Organ pipe coral (Tubipora musica) produces a vivid red skeleton of perfectly parallel calcified tubes — one of the most architecturally distinctive structures on the reef. Each tube houses a single polyp. When disturbed, all polyps retract simultaneously.
The bright red color of organ pipe coral's skeleton is permanent — it comes from iron salts embedded in the calcium carbonate during growth, not from pigment cells. The skeleton retains its red color long after the coral dies.
Lettuce Coral
Lettuce coral (Turbinaria reniformis) grows in ruffled, folded whorls that strongly resemble the leaves of a head of lettuce. The convoluted shape dramatically increases surface area, allowing the colony to pack more zooxanthellae per square metre of reef footprint.
Lettuce coral is one of the most tolerant coral species — it handles water temperatures, turbidity, and low salinity that would bleach most other corals. Scientists study it as a model for reef resilience under climate change.
Star Coral
Star corals (Montastraea and related genera) are massive boulder-shaped colonies whose surface is studded with star-shaped polyp openings — the pits that give the coral its name. They are foundational reef builders and can live for hundreds of years.
Star corals are one of the most important spawning corals on Caribbean reefs. Once a year, after the full moon in August or September, entire populations release eggs and sperm simultaneously in a massive synchronized broadcast.
Sea Star
Sea stars are echinoderms that prowl reef floors, preying on bivalves, coral polyps, and detritus. They feed externally — everting their stomach out through their mouth to digest prey outside their body before drawing it back in.
Sea stars can regenerate entire lost arms, and some species can regrow a complete new body from a severed arm with just a small piece of the central disc still attached.
Sea Urchin
Sea urchins are voracious reef grazers whose dense spines deter most predators. They use five continuously growing teeth (Aristotle's lantern) to scrape algae from rock surfaces. When populations collapse, algae explosions can destroy reefs.
In 1983–84, a mysterious disease killed over 97% of long-spined sea urchins across the Caribbean. The loss triggered an algae explosion that smothered reefs from which many have still not fully recovered.
Nudibranch
Nudibranchs are shell-less sea slugs renowned for their extraordinary colors. They are carnivores that feed on sponges, hydroids, and other nudibranchs. Many species sequester toxins from their prey for their own chemical defense.
Some nudibranchs feed on stinging hydrozoids and store the unfired nematocysts (stinging cells) in their own skin, redeploying them as a stolen defense — a process called kleptocnidae.
Sea Snake
Sea snakes are air-breathing reptiles fully adapted to marine life. They hunt reef fish and eels in crevices, using venom many times more potent than a cobra's to subdue prey. Despite their potency, they rarely bite humans unprovoked.
Sea snakes have a paddle-like tail for swimming but cannot move on land at all. Unlike sea turtles, some species give birth to live young underwater and never come ashore throughout their entire lives.
Scuba Diver
Scuba divers are among the most frequent human visitors to coral reefs. Recreational diving is a multi-billion dollar industry, but careless divers can break coral, stir up sediment, and stress wildlife. Responsible divers are reef ambassadors.
A single accidental fin kick can break coral that took 10 years to grow. "Look but don't touch" is the cardinal rule — trained divers maintain neutral buoyancy to hover without ever making contact with the reef.
Research Submarine
Research submersibles venture into deep reef systems inaccessible to divers, collecting samples, mapping habitats, and capturing footage of rarely seen species. Many deep-reef creatures have never been observed outside of submarine expeditions.
The Pisces IV and V submersibles have documented over 400 coral species in the "twilight zone" reefs (60–150 m) off Hawaiʻi — a habitat so poorly studied that new species are discovered on nearly every dive.