Coral Reefs of the Red Sea

Dr Anjani Ganase, coral reef ecologist, compares coral ecosystems of the Red Sea and the Caribbean. Coral scientists around the world are monitoring their native reefs as well as those that have adapted to higher temperature, looking at coral refuges.

In the Old Testament, the passage through the Red Sea is a miracle created by God, to allow the Israelites to leave Egypt, led by Moses. The Red Sea was first explored by the Egyptians and Greeks looking for routes for trade between Africa and Asia. It is not a large body of water, in fact, it is one sixth the size of the Caribbean Sea, but it is long (2,250 km) and narrow (355 km wide – distance between Trinidad and St Lucia) stretching from the Gulf of Suez, where the Suez Canal connects to Mediterranean Sea. To the south, the Red Sea flows into the Indian Ocean. Geologically, the Red Sea is part of an extensive rift system that runs north–south all the way down the African East Coast to Mozambique, and is part of the Great Rift Valley system. It is actually one of the planet’s youngest basins, and continues to expand through the centre of the basin.

The name Red Sea has a couple possible origins. In ancient languages of the region, “red” means south just as “black” – as in the Black Sea - refers to north. The other theories behind the Red Sea name are more ecological in origin, relating to the cyanobacteria (Trichodesmium erythraeum) that blooms in the Red Sea occasionally turning the normally aquamarine sea to a reddish-brown colour. The unique geography and resulting ecology of the system, as result, are fascinating for marine research.

Coral reef, Sharm el Sheikh, Egypt. Credit: Renata Romeo / Ocean Image Bank

 

VERY SALTY VERY HOT

Unlike Trinidad and Tobago, whose surrounding waters are flushed by the nutrient-rich freshwater of the Orinoco, especially during the rainy season, the Red Sea is one of the saltiest bodies of water on the planet. It occurs in a very hot and dry location, bordered by six desert countries which means that not a single river flows into the Sea. No freshwater influx and high evaporation result in very salty conditions. The low nutrient, warm and transparent water makes it ideal for some extensive coral reefs that fringe most of the coastline around the Red Sea. The coral reefs there are home to over 1000 invertebrates, and 200 species of soft and hard corals. Compare with the larger Caribbean Sea which is home to about 180 hard and soft corals, and Trinidad and Tobago which is home to a much smaller subset.

The Red Sea is rich in endemic species (marine species found in no other seas or oceans) and these make up 15 % of its biodiversity, and there are species in common with the Indo-Pacific region. This endemism is the result of the unique environment. There is connectivity, however limited, via the narrow strait called Bab-el-Mandeb Strait which is 20 miles wide with the Indian Ocean.

In the Caribbean Sea, you will find no corals in common with any other region in the world. The Caribbean is more unique with high endemism of hard coral species.  If you dive in the Red Sea it will be like diving in another world with very few similarities with the Caribbean.

The Red Sea is still quite a unique marine environment compared to other coral reef regions as well. The basin of the Red Sea is relatively shallow with 40 % of the basin being less than 100 m in depth. The deepest section occurs along the mid-ocean ridge. The deepest area is the Suakin Trough which is just over 3000 m deep. While the EEZ around Trinidad and Tobago is relatively shallow as our islands sit on the South American continental shelf, there are areas that drop to about 3500m deep.

The Red Sea from space. The Nile River and the Red Sea lead to the Mediterranean Sea and are pictured from the International Space Station as it orbited 258 miles above the Arabian Peninsula. A pair of the space station's main solar arrays drapes across the left foreground. NASA

 

RED SEA CORALS LIKE THE HEAT

The water is also naturally very warm, meaning that corals in the Red Sea naturally have a higher thermal tolerance. The tolerance limit for Red Sea corals (in the south) is about 32 – 34.5 C, while Tobago’s corals become severely stressed above 29 C. This means that the Red Sea might be the perfect ecosystem to explore for coral adaptation to a warmer planet. This does not, however, mean that the marine life of the Red Sea is immune to global warming, with temperatures expected to increase 2-4 C by the end of century. Coral reefs in the Red Sea, similar to reefs in other regions around the world have experienced an increasing number of bleaching events since 1998. Nevertheless, given the higher thermal tolerance especially of the coral reefs in the north, they are considered by scientists to be a coral refuge.

The Red Sea boasts a thriving diving tourism, but coastal development, and growing human populations, especially along the Saudi Arabian coast, are increasing human impacts to the reef systems in the form of pollution and habitat destruction.

FROM THE RED SEA TO THE CARIBBEAN

As ocean temperatures continue to rise, scientists are looking at places where corals tolerate higher temperatures. The challenge is not simply to monitor the reefs and coral species in our islands; but to be aware of the reefs that may have already adapted to heat and stressors that are now increasing in the Caribbean. On land, some species are slowly migrating to places where conditions are becoming what they have been accustomed to. Will migration ensure survival of some coral species?

 

Turtle over Thomas Reef, Egypt. Credit: Renata Romeo / Ocean Image Bank