Dendronephthya is a genus of soft corals known as carnation, cauliflower or tree corals: inflated, branching colonies studded with clusters of polyps in red, pink, orange, purple, yellow and white. Unlike most reef corals they have no zooxanthellae, the symbiotic algae that feed reef-building corals with sugars from sunlight. Instead they live on food filtered from the current, and the surprise discovered in the 1990s was that most of that food is phytoplankton.

It is a huge genus. The World Register of Marine Species (WoRMS) listed 247 accepted species when we checked in November 2026, and reference works round that to “over 250”. The genus was named by Kükenthal in 1905 and sits in the family Nephtheidae. An older name, Spongodes, is now treated as a synonym. In the reorganised octocoral classification used by recent papers, the family falls in the order Malacalcyonacea.

Those plain facts hide a genus that is unusual in almost every way: a coral that eats plants, a reef animal that dominates where the water moves fastest, a group that clones itself by shedding pieces, and, at the temperate southern edge of its range, an endangered species that almost vanished from its stronghold in two flood seasons.

What does Dendronephthya look like?

A colony is a translucent, water-filled trunk and branches, often with the sclerites visible as a glittering network under the skin. Sclerites are tiny calcium carbonate spicules that stiffen the tissue in place of a solid skeleton. The branches end in bundles of polyps, each with eight tentacles, the hallmark of all octocorals. The tentacles are lined with side branches called pinnules that increase the surface area for filtering. Each polyp bundle is guarded by long, sharp supporting sclerites that stick out like thorns.

The colony’s shape depends on water movement. With the current running, it fills with seawater and stands upright, branches spread and polyps open. When the current slackens, it deflates into a small, limp lump. A 2015 study by Davis and colleagues in Marine Biology examined how colonies of the Australian species D. australis extend in tidal current flows, and the Red Sea species D. hemprichi opens its polyps and releases gametes only when flow is between about 3 and 25 cm per second.

Size varies by species and site. Dendronephthya hemprichi, the best-studied species, reaches up to about 70 cm and is usually pink or orange with a see-through trunk. White’s seahorses in Australia showed a significant preference for D. australis colonies taller than 40 cm, which gives a sense of how large temperate colonies can grow.

The colours are produced by the coral’s own tissue and sclerites, not by algae, which is why carnation corals are brilliant rather than the browns and greens of many photosynthetic soft corals. That gives a rough field rule. If a tree-shaped soft coral is brown or green, it probably contains algae. If it is brilliant red, pink or purple and translucent, it is probably Dendronephthya or a close relative such as Scleronephthya, and it depends on what the water brings it.

Why are there so many species, and how are they told apart?

The long species list is largely a product of early 20th-century museum work. The WoRMS list is dominated by names from a handful of authors: Kükenthal in the 1890s to 1910s, Henderson in 1909, Utinomi in Japan in the 1950s, Tixier-Durivault and Prevor in France in the late 1950s and early 1960s, and Verseveldt, sometimes with van Ofwegen, from the 1960s to 1991. The oldest species name in the genus, D. florida, dates to Esper in 1791, long before the genus itself existed.

Most of these species were described from preserved specimens, and in soft corals preservation destroys the very features a diver notices: colour, the inflated shape and the way polyps sit. Identification instead rests on the sclerites, which have to be dissolved out of the tissue and examined under a microscope, and on how the polyp bundles are arranged. Even then, the boundaries between many species are uncertain. A field photograph alone rarely gets beyond “Dendronephthya sp.”.

Genetics is starting to help. In 2022 Williamson and colleagues used DNA analysis to confirm that the Australian D. australis is a single species in the family Nephtheidae, backing up identifications that had been based on morphology alone. A 2023 study of a Mediterranean colony used both genetic and morphological testing before suggesting it was probably D. hemprichi.

How does Dendronephthya feed?

For most of the 20th century, corals without algae were assumed to live by catching zooplankton, the tiny animals drifting in the water. In 1995, Fabricius, Benayahu and Genin overturned that idea in Science. They showed that a zooxanthellae-free soft coral from the Red Sea fed almost exclusively on phytoplankton, a mode of nutrition then unknown in corals. Three other algae-free soft corals they studied also proved to be plant eaters.

A companion paper the same year in Limnology and Oceanography worked out a carbon budget for D. hemprichi in the northern Red Sea. Phytoplankton uptake and the rate at which colonies added new polyps both responded to water flow, peaking at about 15 cm per second. Polyps grew larger as flow increased from 1 to 32 cm per second. Zooplankton was captured selectively, mostly weakly swimming larvae of bivalves and snails, but it supplied less than 5% of the coral’s carbon needs for growth and respiration, two to three orders of magnitude less than the carbon gained from phytoplankton.

The reason this matters is simple arithmetic. In clear tropical reef water, phytoplankton biomass can be about ten times higher than zooplankton biomass. A coral able to strain microscopic algae from the water taps a far larger food supply than one restricted to animal prey. The authors linked the ability to the narrowly spaced pinnules on the tentacles and to the colony’s adaptations for life in strong flow. Later measurements described phytoplankton being depleted in the water downstream of feeding colonies.

This explains where carnation corals grow. Because they cannot make food from light, they live where food comes to them: steep walls, channels, pinnacles and the undersides of ledges, often in strong current and often in shade. Light is irrelevant to them, so they can occupy overhangs and dim walls where reef-building corals struggle.

How does Dendronephthya reproduce?

Much of what is known comes from Benayahu’s group at Tel Aviv University, working on D. hemprichi at Eilat in the northern Red Sea. Colonies are gonochoric, meaning each colony is either male or female. Dendronephthya hemprichi releases gametes daily over long periods, a pattern described in a 1997 Marine Biology paper as year-round spawning. After release, an egg is briefly held at the polyp’s mouth by a mucus thread, which gives sperm a chance to reach it before it drifts away. Fertilised eggs develop into swimming larvae called planulae.

The genus also clones itself. In a 1997 paper in Coral Reefs, Dahan and Benayahu described D. hemprichi shedding small fragments, 2 to 5 mm long and made of just a few polyps, over a period of about 20 hours. A single colony can release hundreds at once. The fragments settle more often on upper horizontal surfaces and less often on vertical ones, but colonies on vertical surfaces survive better because they intercept more phytoplankton in the current. Around Eilat, many of the vertical surfaces colonised in this way are the pilings of oil jetties.

That quick colonisation has a practical side. Dendronephthya hemprichi was used on artificial reefs at Eilat to attract divers and support local wildlife. There it ended up on the undersides of horizontal plates, because the stony coral Stylophora pistillata outcompeted it on the upper surfaces.

The Australian species has now been studied in the same detail. In 2023, Larkin and colleagues published the first description of its reproduction, using tissue analysis and 19 years of photographs of colonies in the wild. Mature eggs and sperm sacs developed in February and March 2022. The team spawned colonies in aquaria, documented every stage from embryo to larva to settled polyp, transplanted juveniles back into the field and watched them grow to as many as 435 polyps in six months. They also recorded colonies fragmenting to clone themselves. The results confirmed that D. australis is gonochoric and probably a broadcast spawner, with spawning likely spread over five months, from November to March, as the water warms. In a public summary, the authors reported that females spawned around the neap tides, when currents are slowest, and that roughly 280 baby corals were produced within a few weeks from a few fragments.

Where does Dendronephthya live?

The genus ranges from the Red Sea across the Indian Ocean to the western Pacific, and south into temperate waters off south-eastern Australia. In the Red Sea, D. hemprichi lives on steep slopes from about 1 to 32 m deep, overlapping with D. sinaiensis, which occupies roughly 11 to 32 m. The Eilat populations sit at about 30° north, near the northern limit of tropical reefs.

The genus is now spreading into the Mediterranean. In May 2023, divers running a long-term ecological survey off Israel found a Dendronephthya colony at 42 m. Genetic and morphological tests suggested D. hemprichi, a species common in the Red Sea. The researchers, led by Nativ, treated it as a probable migrant through the Suez Canal favoured by warming water, and predicted that its fast attachment and growth would let it spread. Colonies have reportedly since been photographed off Byblos, Lebanon.

Dendronephthya australis is the temperate outlier. It is endemic to south-eastern Australia, where colonies have been recorded over about 400 km of coast, from Seahorse Gardens in Port Stephens south to Jervis Bay. Unusually for a coral, it grows in estuaries swept by tidal currents.

Why is the Australian cauliflower coral endangered?

Dendronephthya australis is listed as Endangered in Australia and is a habitat-forming species. Its colonies shelter young snapper and the endangered White’s seahorse, Hippocampus whitei. In a four-year study in Port Stephens, adult White’s seahorses preferred sponges and D. australis colonies as holdfasts, favouring colonies taller than 40 cm and avoiding those under 20 cm.

Before 2021, the marine-dominated eastern part of Port Stephens, an estuary about 250 km north of Sydney, held the world’s largest aggregations of the species. Then came La Niña. In March 2021, several days of rain fell along about 450 km of the New South Wales coast, and Port Stephens recorded its wettest week on record. Floods followed in March 2022 and June 2022. Monitoring from 2019 to 2022, reported by Larkin and colleagues, found that the March 2021 flood alone caused a 91% decline in the remaining area covered by the coral. Colonies in shallower water, where salinity dropped furthest, were hit hardest. By the end of 2022 every remaining aggregation in the estuary had been lost, leaving the species on the brink of local extinction there.

Disease has struck too. At Bare Island in Botany Bay, Sydney, Steinberg and colleagues watched a necrotising disease spread from December 2019 to January 2020, causing polyp loss, lesions and the collapse of the colonies’ internal canals. By September 2020 every large colony was gone and only a few scattered recruits remained. Recovery was quicker than feared: new recruits appeared within 10 months and large colonies within 18 months, so the authors concluded that restoration was not needed at that site.

Genetics adds another warning. Williamson’s 2022 study found that the Jervis Bay population was genetically distinct, with low diversity and signs of a recent population crash and bottleneck. Port Stephens and Ettalong, about 150 km to the south, held the most genetic diversity and may have acted as refuges, which is why their losses are so worrying.

Restoration is under way. Building on the reproduction study, the team fertilised eggs in the laboratory, transplanted hundreds of juvenile corals and released thousands of larvae into Port Stephens. Early results suggested some lab-bred corals survived at least 18 months and did better than corals grown from fragments. Because each colony is a single sex and fertilisation depends on males and females being close together, the authors stress that restoration must include both sexes.

Is Dendronephthya harmful or useful to people?

The main documented health problem with carnation corals is allergy. Along the Pacific coast of Miyazaki Prefecture in Japan, spiny lobster fishermen who handle tangled nets developed occupational allergies, including conjunctivitis, rhinitis, dermatitis and bronchial asthma, traced to the red soft coral Dendronephthya nipponica. In 2001 Onizuka and colleagues showed that the coral’s sensitising activity lay in molecules of 10 kD or larger. Later work found a related allergen in another octocoral, Scleronephthya gracillima, belonging to a family of proteins similar to the green fluorescent protein.

The genus is also a chemical treasure chest. A 2020 review in Molecules by Chen and colleagues listed 170 natural substances isolated from Dendronephthya species, including steroids, terpenoids, peptides and prostaglandins, some with potential biological activity.

Why is Dendronephthya so hard to keep?

The feeding research explains the problem. A wild colony is sustained by a constant stream of microscopic algae delivered by currents of several centimetres to tens of centimetres per second, with peak feeding around 15 cm per second. A typical home reef tank is deliberately kept low in nutrients and plankton, and its lights and flow are designed for photosynthetic corals. A Dendronephthya in that environment has nothing to eat. Reference sources describe the genus as notoriously difficult, needing a near-constant supply of small foods such as phytoplankton.

A few specialists keep them in dedicated non-photosynthetic systems, with continuous dosing of live phytoplankton and fine foods, strong alternating flow and excellent filtration to handle the extra nutrients. If you do not plan to build such a system, leave them on the reef. Carnation corals are not a beginner’s purchase, and their survival rate in ordinary tanks is poor. The best way to enjoy Dendronephthya is underwater.

Where can divers see carnation corals?

Look for current. Carnation corals are most spectacular on drift dives along walls, channels and pinnacles, where colonies inflate and face into the flow. Turn on a torch, even in daylight, because many colonies grow in shade under overhangs and their true colours only show under artificial light.

Good diving manners matter more than usual. Inflated colonies are soft, full of water and easily torn by fins, tank bangers or a grabbing hand on a current-swept wall. On busy dive reefs at Eilat, studies have found that branching and bottom-dwelling corals suffer higher rates of damage from recreational divers. In Australia, divers at Port Stephens and Botany Bay can help by reporting healthy or diseased D. australis colonies to local researchers.