One and only

It could be claimed that the underwater life of the Red Sea is more vivid and colourful than anywhere else on the planet. One, particularly imaginative, explanation for this is when the angels were painting the world, they took a little ‘siesta’ in this part of the world and accidentally spilled all the leftover paints in the Red Sea. Another, more conventional, explanation is the process of evolution. 

The main reason why an unusually high number of species have evolved in the Red Sea unfound anywhere else on Earth, is the Red Sea’s near enclosed shape. Known as ‘species endemism’, only the remote Hawaiian Islands archipelago has a greater number of endemic species than the Red Sea. As continental plates drifted apart, species isolated in certain areas, such as animals on a landmass surrounded by water, or as in the case of the Red Sea, a sea surrounded by land, evolved to suit the specific needs of the surrounding environment. As evolution of the trapped species progressed, unique species formed in each area, all of which are perfectly suited to the specific ecological niches of their environment. 

Five million years ago the Red Sea was connected to the Mediterranean by a narrow channel. This channel was eventually closed as the continents gradually rose leaving the Red Sea an enclosed basin, isolating the species in the Red Sea from their relatives elsewhere. Later, the southern Red Sea opened into the Indian Ocean, now known as the Strait of Perim or Bab el Mandeb. Today, this channel is the narrowest and shallowest section of the Red Sea and still acts as a physical barrier to the movement of many reef species in and out of the Red Sea. As a result, the perfect environment has occurred, formed over the millennia for the evolution of unique endemic species. Thanks to this evolutionary process, not only is the marine life of the Red Sea so vibrant, but approximately 20 percent of the species present are completely unique. Many of these species are commonly found in Egyptian waters and are regularly encountered by divers and snorkellers.

The Red Sea is home to 300 species of corals, 10 per cent of which are endemic. The common brain coral (Erythrastrea flabelleta) found on all Red Sea reefs and characterized by a winding pattern of cream coloured polyps found on reef slopes down to 20m is a classic example of a Red Sea endemic species.

The most noticeable and colourful of all Red Sea endemics, are the fish.The Red Sea bannerfish (Heniochus intermedius) is one of the endemic fish species of the Red Sea most easily recognized by divers and snorkellers in Egypt. They occur in pairs or small groups on the reef and feed on small invertebrates and zooplankton.

Butterflyfish flourish in all tropical seas, with 12 species listed in the Red Sea. Half of these species are endemic. Being small and territorial, when isolated by the moving continents, they quickly evolved as a different species to their cousins outside the Red Sea. Butterflyfish range in size but are generally small, from 10 – 20cm, they occur normally in pairs or small groups and inhabit only healthy reef systems, where they feed on tiny coral polyps, algae and zooplankton and even jellyfish.

One of the most iconic Red Sea reef fishes, the blue-cheeked butterflyfish (Chaetodon semilarvatus) is an endemic species. Easily recognized by its bright lemon yellow body, blue cheeks and larger build compared to other butterflyfish, they occur in pairs close to the reef. On occasion they can be seen schooling in large numbers with the Red Sea bannerfish. Being territorial, they are often encountered in exactly the same part of the reef on different dives.

The orangetail butterflyfish (Chaetodon paucifasciatus) is another territorial butterflyfish. Small in size with distinct striped markings and an orange stripe through the eye and orange tail they can be seen in disputes with members of the same species as they try to defend the favoured table corals on which they feed. 

More mobile species of butterflyfish can be found cruising the reef in search of food. The threadfin butterflyfish (Chaetodon auriga) and racoon butterflyfish (Chaetodon fasciatus) are colourful common species that can be seen throughout the Red Sea nibbling on coral polyps as they move along the reef. The Giant butterflyfish (Chaetodon lineolatus) is, as its name suggests, the largest Red Sea butterflyfish, while the ornate (Chaetodon austriacus) is one of the most beautiful, and the orange-faced butterflyfish (Chaetodon larvatus) is the rarest of all.

The sohal surgeonfish is a Red Sea endemic that inhabits the shallow reef flats of reefs. It is a strikingly beautiful fish with black and white stripes and a bright orange razor sharp spine at the base of its tail. The Sohal (their Arabic name) are extremely aggressive towards other fish that may venture into their territory and will even defend their patch from snorkellers or divers. They feed on algae that grow on the bare rock of the reef. 

Being isolated, endemic species are particularly prone to environmental threats both manmade and natural. The declining state of the world’s reefs from destruction by man, climate change and pollution are well documented and these threats can have an even greater effect on the presence of endemic species in areas such as the Red Sea. Simply put, once numbers of endemic species start to fall it can be nearly impossible for the numbers to increase because of the limited size of the population.

In the Red Sea all species face threats from man in the form of reef reclamation to provide foundations for the spread of coastal development as well as coral bleaching caused by increased sea temperatures depriving the endemic fish of their shelter and food sources, while physically killing endemic coral species.

The sheer beauty of many endemic species, in particular the butterflyfish, makes them massively attractive in the aquarium trade. Fishermen throughout the Red Sea, often acting illegally, catch huge numbers of reef fish that are sent to all four corners of the globe to satisfy the increasing demand for live tropical fish. This added pressure on the endemics of the Red Sea impacts greatly on these unique species and may even go some way to tipping the balance into a downward spiral with inevitable consequences.

An awareness of not only the existence of Red Sea endemic species, but also their importance, will help visitors to Egyptian reefs conserve the reef organisms that they love to see. Do everything in your power to help promote conservation and reduce your impact on the marine environment. Enjoy spotting endemic species while out on the reef and always remember that they are prettier sight in the wild than in an aquarium at home.

By Owen Bruce
First published in BLUE magazine March 2010