Red Sea Endemics: Extraordinary Marine Species Found Nowhere Else on Earth

Did you know that around 20% of all the fish that you may encounter in the Red Sea are not found anywhere else on the planet? Lawson Wood tells us more about these colourful Red Sea endemics.

How the Red Sea Formed and Why It Matters for Marine Evolution

The formation of the Red Sea started some 180 million years ago when the crust started to sag during the tectonic movements between the African and Arabian land masses. Over the next 140 million years or so, this continued until the Oligocene era (38 million years ago) with a very distinct rift having been formed.

Over the next 125 million years the rift valley was either a highly saline sea (much like the Dead Sea of today in Israel) or more commonly dry land, with deep salt deposits and clear connections between Kenya, all the way northeast to the Holy Land. The seabed was always in constant turmoil and as well as the several ancient volcanos at the Brothers, Daedalous and Elphinstone Reefs, there were massive deep vents with deposits of metalliferous muds – essentially these are the famous Red Sea hot brines which are attracting much scientific interest.

Isolation, Salt, and Survival: The Recipe for Endemic Species

The most-massive change occurred around five million years ago when this sunken basin became a huge evaporation plain with dried salt deposits, sometimes hundreds of metres thick. The Red Sea valley was still connected to the Mediterranean at this time, yet closed off to the rest of the Indian Ocean in the south. The shallower area in the Straits of Tiran was also closed off and the Gulf of Aquaba was similarly isolated at the same time. Tectonic movements further isolated the region of the Dead Sea and during the Pleistocene era, the waters that formulated this region came from the Mediterranean. However, most theories state that the Jordan Valley, where the Dead Sea is found, is part of the same Great African Rift Valley that has formed the Red Sea.

Continental upheaval eventually closed off the northern connection, yet volcanism opened up the Straits in the south at Bab el Mandeb and the greater Indian Ocean rushed into the Red Sea filling the void, bringing hundreds of species of fish and planktonic larval corals and invertebrates, ready to colonise the sea once more. While the last ice age never reached the region, the planetary influence was so globally overpowering that the sea level dropped around 100m and once more the Red Sea was isolated again. Some scientists believe that the adjacent regions of cold-water upwelling off Somalia and Oman, as well as seasonal current patterns, are of greater importance as isolating mechanisms than the physical isolation at Bab al Mandab, undoubtedly these are important factors and indeed these upwellings still have a huge influence on the Red Sea, but now that the channel is open into the Mediterranean, the tidal flow has also increased.

This was the time when the creatures trapped in this isolated sea started to subtly change from their oceanic counterparts. Around 15,000 years ago, the sea level rose once more at the end of the last ice age and a curious mixture of oceanic and endemic species began to live in that perfect harmony which we all so love today. In reality, this is a new sea with its coral reef systems only around 5,000 years old, yet founded upon ancient coral exoskeletons laid down between the inter-glacial periods over millions of years.

The Red Sea is, in fact, an extension of the Great African Rift Valley, which was once the pathway for the earliest humans to migrate out of Africa (I actually found a couple of hand-tooled flint arrowheads at the tip of the Sinai Peninsula literally many hundreds of miles from any source of natural flint!), this 2,250km long sea evolved to became a shipping highway as the world’s nations used the sea to bring spices and produce from as far away as China. Now with the Suez Canal and the link once more open to the Mediterranean, the Red Sea is one of the busiest water highways on the planet. Under these surface waters, ecological factors continued the sub-specie development and the Red Sea has grown to become a true centre of evolution.

What Makes Red Sea Waters So Unique?

While the Red Sea valley is still on the move, its physical constraints mean that it has virtually no tidal influence or range in sea levels, the water is warm all year round and with its steep sloping sides and vertical walls, sediment tends to sink quickly, resulting in clear, clean water all year round. The movement is pushing east around 2.5cm per year and should you wish to extrapolate this further, then in the next 100,000,000 years this region will have a new ocean over 2,500km wide! There is a higher salt content to this sea, but this only helps the resident critters to feel their best in their watery home.

The Sea has three distinct zones: there is the shallow live coral reefs around the fringes and offshore islands to around 60m; the next zone has a steeply sloping seabed to between 500-1,000m, and below this is the median trench with depths over 3,000m in a hot brine zone between Port Sudan and Jeddah in Saudi Arabia, making the Red Sea one of the deepest seas in the world.

The Red Sea has around 1,200 species of fish in 159 different families; some 200 different types of soft and hard corals and another 1,000 or so different invertebrates, with around 10 -20% of all fish species found in the Red Sea being endemic. As this is the closest tropical reef to mainland Europe, inevitably it attracted a massive amount of scientific and biological interest, and Peter Forsskål was one of the first scientists in the 18th century to influence our understanding of the Red Sea’s flora and fauna. Many eminent others followed in his steps and all have species named from their observations and collections.

What’s in a name?

All marine species have a common name and a proper (Latin) name. Common names can change from region to region, never mind country to country, hence the use of proper scientific names to remove this confusion.

Kingdom: Animalia
Phylum: Chordata
Class: Actinopterygii
Order: Perciformes
Family: Pomacentridae
Genus: Amphiprion
Species: A. bicinctus

Binomial name 

Amphiprion bicinctus
Rüppell, 1830

As we can see with the naming of the Red Sea anemonefish; two-striped anemonefish; two striped clownfish; clownfish or Red Sea cClownfish, you should be trying to describe the same fish, but thankfully the full Scientific Classification is on hand to properly describe its place in the hierarchy of all living things, including who first described the fish, back in 1830: The Zoological scientist and Geographer Eduard Rüppell from the Senckenberg Research Society and Museum in Frankfurt.

This series of Classification was first discussed by Pliny the Elder (Gaius Plinius Secundus) who was a Roman author, naturalist and natural philosopher during the first century AD. He was 56 when he died during the eruption of Vesuvius in AD79. The volumes in his Naturalis Historia include an encyclopaedia of animal and marine life. However, it wasn’t until the 18th century when the system of binomial nomenclature was first used for the naming of organisms by Carolus Linnaeus. His Systema naturae was first published in 1735.

The use of scientific names quite clearly removes any confusion about the name of the animal and its name is divided into two parts. The first name is always capitalised and is the name of the Genus or family which is regarded as the Generic name. The species is always the second name and this is never capitalised. The Genus is used to describe all of the animals or fish which have the same overall characteristics and are possibly capable of interbreeding and having fertile young. Species descriptions are in Latin and will describe the particular characteristics of the creature, but of course, there are always exceptions and these are when the discoverer of a particular species has their name attributed as the species description. It is the Generic name and the specific name which gives each species its unique binomial name. These names are always printed in Italics and usually in brackets, hand-written Latin names are always underlined.

As always, there have been problems in identification when the colouration of male and female species may be radically different as well as several colour stages during the younger fish reaching maturity and then subsequently changing sex. There have been a number of notable explorers of the Red Sea who have fished, dredged, netted and captured virtually every species that we see and their names crop up regularly in most species descriptions, as the original discoverer. This auspicious bunch include Linnaeus; Rüppel; Bloch; Forster; Klunzinger; Hemprich; Hickson; Rousseau; Henderson; Schultz; Boyl; Forsskål; Yong; Steinitz; Mertens; Dollfus; Fridman and my good friend Helmut Debelius, who discovered a dwarf species of seahorse (which I am still searching for!). All marine scientists who have been allowed the honour to have species named after them.

Commonly used Latin and Greek stem words used in the naming of species

• acanth (Gr) thorn: Acanthurus – surgeonfish (caudal spines)
• aetos (Gr) eagle: Aetobatus narinari -eagle ray
• chaet (L) bristle: Chaetodon – butterflyfish (bristle-like teeth)
• cubicus (L) cube or box: Ostracion cubicus – yellow boxfish
• dimidiatus (L) halved: Labroides dimidiatus – cleaner wrasse (half blue, half black) also bicolour puller Chromis dimidiate (half black, half white)
• lineatus (L) with lines: Plotosus lineatus– lined eel catfish
• Pterois – scorpionfish: Pterois volitans – common lionfish (wing-like pectoral rays)
• scaros (Gr) parrotfish: Scaridae – parrotfish
• sepia (GR/L) cuttlefish: Sepia prashadi – hooded cuttlefish
• taeniatus (L) striped: Pseudanthias taeniatus Red Sea fairy basslet

Local Names

• Bajad: Arabic name for the jack or goldbody trevally (Carangoides bajad)

Location Names

Species named after the location where the animal was first described:-

• winged oyster (Pteria aegyptiaca)
• Egyptian sea star (Gomophia aegyptiaca)
• Egyptian prawn (Metapenaeopsis aegyptiaca)

Back to the Red Sea and with this new understanding why there has been such a significant evolution in endemic species. Imagining, as the scientists have proven, that the epicentre for marine life was in what is referred to as the Golden Triangle (that little area of Indonesia where the tectonic plates shifted Australasia from Asia as pioneered by Alfred Wallace, who published his paper on Natural Selection a year before Darwin). The ‘Wallace Line’ is the adopted name for that channel in the Malay Archipelago which divides the two great continents.

As the tectonic plates moved the land masses around our planet, they also provided the means for the distribution of all terrestrial and marine life, hence several million years later, the Hawaiian archipelago has 30.7% of its fish as endemic species and Easter Island has 21.7%. Further away west, the Red Sea has 12.7% (16.7% when combined with the Gulf of Aden) of fish species; all the more reason for us to try and find them all! The great thing is that there are so many other endemic species with perhaps as many as 10-20% of all species developed in the Red Sea when it was completely cut off and with a higher salinity than the rest of the outer oceans at around 4.2% as opposed to 3.8% in the greater Indian Ocean.

Now that the man-made opening to the north where the Suez Canal linked Port Said with Alexandria, this inevitably influenced the spread of the Red Sea species into the Mediterranean since 1869, these Red Sea endemics have been influencing the eastern Mediterranean ecosystem since then. There was a natural stop-gap in the Bitter Lakes midway along the Suez Canal and this restricted much of the Mediterranean invasion. However, in 2015, the Egyptian Government decided to widen and dredge the Canal to allow for larger ship traffic. Unfortunately, as a consequence of this, what has happened with this development is that there is nothing to stop the now much greater flow of water that comes from the greater Indian Ocean and the Red Sea directly into the Mediterranean.

Now visitors to the eastern Mediterranean are enjoying tropical angelfish, soldierfish, parrotfish and many others, not least of all – the lionfish (Pterois volitans). This fish, which has wreaked havoc throughout the Caribbean, is now on track to do the same thing in the Mediterranean and early indications are that the species has spread west as far as Malta, Sicily and Sardinia, and as far north as Croatia. Undoubtedly, not only is there now a fast-flowing supply of invertebrates and fish, the water column is also so much warmer, this will inevitably have further consequences for the resident Mediterranean populations.

As the tectonic plates moved the land masses around our planet, they also provided the means for the distribution of all terrestrial and marine life

Similarly in the southern opening into the wider Indian Ocean, many endemic Red Sea critters have spread out against the prevailing currents at Bab el Mandeb (meaning Gate of Lamentations) where it is 29km wide at this point and only 130m deep, making it the narrowest and shallowest part of the sea, and are now being found all around the Arabian Gulf and some, even further down the mainland African coast. The Arabic common name for this sea is al Bahr al Ahmar (basically a translation of the European name).

Some of the more-common species found on every dive include Fridman’s dottyback (Pseudochromis fridmani). This brilliant (almost) neon purple little basslet can be found on all of the reef walls, in large numbers, in all depths and is so common it is almost incredulous that this little fish is relatively new to science. Another couple of endemic basslets which we can find on almost every dive are the Red Sea fairy basslet (Pseudanthis taeniatus) and the red striped fairy basslet (Pseudanthias fasciatus). These basslets or dottybacks and another half dozen are all only found in the Red Sea as well as a surprising number of wrasse, damselfish, parrotfish and grouper.

One of the smaller critters is the Red Sea Chelidonura (Chelidonura livida), a type of nudibranch or sea slug that lives on coarse sand and is a velvet black in colour with iridescent blue spots and circles, but usually only seen on night dives. Further up in size is the amazing panther cowrie (Cypraea pantherina) which is a close relative of the Indo/Pacific tiger cowrie. The winged oyster (Pteria aegyptiaca) is also endemic to the region with close relatives in the greater Indian Ocean, like so many of the species which have evolved to life in the Red Sea.

Amazingly, as many of us are regular visitors to the Red Sea, a large proportion of our most common sightings are endemic, particularly in the butterflyfish family and these include polyp butterflyfish (Chaetodon austriacus); striped butterflyfish (Chaetodon fasciatus); masked butterflyfish (Chaetodon semilarvatus); Red Sea bannerfish (Heniochus intermedius) and the redback butterflyfish (Chaetodon paucifasciatus). Another surprising endemic is the masked puffer (Arothron diadematus) as we see them on every dive and each evening at the tip if the corner at Ras Zatar near Ras Muhammed and south on Panorama Reef, they school together in large numbers. Another very small pufferfish which is endemic to the region is the pygmy pufferfish (Canthigaster pygmae), more often found on night dives when it rests in the corals. Even the garden eels here are endemic, the Red Sea garden eel (Gorgasia sillneri) is found in many areas, as is the Red Sea eightline wrasse (Paracheilinus octotaenia), but is quite difficult to find. The most obvious of the echinoderms that we can encounter on night dives is the toxic leather sea urchin (Asthenosoma marisrubri). Beware of those little white dots of poison on the tips of their tentacles!

There are also a couple of species of triggerfish such as the bluethroat triggerfish (Sufflamen albicaudatus) and of course we all recognise the Sohal surgeonfish which can be found in all the shallow reef and wreck zones. A couple of real rarities are the crested velvetfish (Ptarmus gallus) and the Red Sea walkman (Inimicus filamentosus), which are more common in the southern Red Sea, very similar to species found in the Indo/Pacific, they are a delight to find in the Red Sea. One of my favourites is the harlequin filefish (Oxymonacanthus halli) – at only a few centimetres long, this has to be one of the cutest Red Sea fish ever!

Of course, by far the most recognised of all the endemic fish is the Red Sea anemonefish (Amphiprion bicinctus). Found on every dive in all areas of the Red Sea, this anemonefish is on the move and has been recorded in the Arabian Sea, but it is very closely related to Clarke’s anemonefish (Amphiprion clarkii), so there may be some confusion. This brightly coloured little ‘Nemo’ hasn’t been found in the Mediterranean – yet! Anemones can live without anemonefish, but anemonefish cannot live without their host anemone. I guess we will just have to watch that space.

Whenever you are visiting the Red Sea be conscious of how many rare and not so rare endemic species that you encounter on almost every dive and revel in the fact that much of what you are observing is not found anywhere else on the planet. The Red Sea is that massive melting pot and being so close to home, it is the perfect coral reef for exploration.

Frequently Asked Questions