Red Sea ecosystem

• Category: Marine and Oceanic Biomes.
• Geographic Location: Middle East.
• Summary: This predominantly shallow inlet of warm saline waters is known for its high biodiversity and unique coral reefs.

Formed by Arabia splitting from Africa, the Red Sea is a long, narrow inlet of the Indian Ocean between Africa and Asia. Informal usage sometimes includes as part of the sea the two gulfs to its north, Aqaba and Suez. The International Hydrographic Organization defined the precise limits of the Red Sea: In the north, it is bound by the southern limits of the Gulfs of Suez to the south point of Shadwan Island, and west to the coast of Africa and Aqaba through Tiran Island, and westward to the coast of the Sinai Peninsula.

The world’s northernmost tropical sea, it is home to 346 hard coral species, 1,700 shallow fish species, and more than 1,000 species of invertebrates. The name Red Sea, used since ancient times, may refer to blooms of sea sawdust or to the arcane use of colors to refer to cardinal directions (in this case, south).

The sea’s coastline is about 1,400 miles (2,253 kilometers) long and an average of 174 miles (280 kilometers) wide. The average depth is 1,600 feet (488 meters), but the water may exceed 8,000 feet (2,438 meters) at its center point. Most of the sea is shallow, and a quarter is less than 200 feet (61 meters) deep.

The Red Sea is surrounded by arid land masses, and due to low rainfall and the high rate of evaporation in the north, it has become one of the most saline bodies of water in the world. Salinity ranges from 36 parts per thousand (ppt) in the south, where water is exchanged with the Gulf of Aden, to 41 ppt in the north, with an average salinity of 40 ppt. By contrast, worldwide average seawater salinity is 35 ppt. Some of the salinity is contributed by highly salty brines emanating from sub-seafloor hydrothermal vents at temperatures approaching 140 F (60 C), a result of the continued widening of the sea due to the tectonic movement of the Red Sea Rift.

Rainfall over the sea and its coasts is low, at about 2.3 inches (60 millimeters) per year, usually in brief thunderstorms. Wind is dominated by persistent northwest winds in the north. The rest of the Red Sea is subject to winds that are seasonally variable in both speed and direction, with speed generally increasing northward. Wind-induced currents shift much of the sediment in the sea, and affect the erosion and accretion of coastal rock exposure. The climate results from the northeasterly and southwesterly monsoons, and the surface water temperature is among the hottest in the world year-round, averaging 72 F (22 C), with summer highs around 90 F (32 C).

The health of the coral reefs here is maintained in part by the great depths of the sea and the efficiency of its water circulation. The water mass of the sea exchanges its water with the Arabian Sea via the Gulf of Aden to the south. The Red Sea is rich in minerals with many sediment constituents. These include nanofossils, foraminifera, pteropods, siliceous fossils, tuffites, volcanic ash, montmorillonite, cristobalite, zeolites, quartz, feldspar, mica, clay minerals, sulfide minerals, aragonite, calcite, dolomite, chalcedony, magnesite, gypsum, anhydrite, halite, hematite, siderite, pyrite, and rhodochrosite. Despite this diverse sediment, the water is exceptionally clear because of the lack of river discharge and the low levels of precipitation.

Biodiversity

The harsh conditions of the hydrothermal vents are inhospitable to most forms of life. The water is hot and highly saline, with high concentrations of heavy metals, and there is little light or oxygen at the bottom of the rift. For many years, the vents were believed to be lifeless, but studies have discovered that, like many other inhospitable parts of the world, they are home to extremophile bacteria and archaea—microbes adapted to extreme conditions. Some such species in the Red Sea include Halorhabdus tiamatea, which is related to H. utahensis of the Great Salt Lake in Utah; H. contractile, which forms tentaclelike protrusions of unknown purpose; and Salisphaera shabanensis, which lives at the interface between the sludgy brine and the seawater.

The sea is surrounded by salt flats characterized by evaporite-carbonate deposits, which form shoals similar to those of the Persian Gulf; long flat salt pans covered in fine-grained alkali salt sediment; and salt marshes that are home to halophytic, or salt-tolerant, plant life and migratory birds.

The coastal zones include stands of grey mangrove (Avicennia marina) and red mangrove (Rhizophora mucronata) trees that are specially adapted to low oxygen and high salinity. A. marina has developed salt glands to rid itself of excess salt by excreting it through the leaves. R. mucronata is found only in the mangrove stands of the Farasan Archipelago, in the southern part of the sea, which is richer in nutrients due to the proximity of the Indian Ocean. As scientists have discovered that mangrove trees are some of the best types of trees for absorbing carbon dioxide, it has become especially important to conserve such stands in the global effort to reduce the negative effects of climate change.

Nearly 100 species of algae are found in mangrove stands, including the sea’s characteristic red algaes, the most common species of which are Bostrychia tenella, Spyridia filamentosa, and Laurencia papillosa. These types dominate in shallow mangrove pools. Blue-green algae is the least diverse algae group, but also the most widespread, growing in both benthic and epiphytic forms throughout mangrove ecosystems.

Local wildlife in the mangrove stands includes mangrove crab species such as the abundant Uca inversa inversa, Metopograpsus messor, Portunus pelagicus, Ocypode saratan, and Macrophthalmus telescopius, as well as a species of mudskipper fish (Oxudercinae).

The Red Sea is the most northern coral reef ecosystem. The most common reef in the Red Sea is fringing reef, which (unlike atolls and barrier reefs) grows close to and often directly from the shoreline. The back reef area has the least species diversity and largely consists of seagrass meadows and the fish that feed from them.

Seagrasses are the only flowering plants that can live completely submerged, and seagrass ecosystems are home to numerous rays and echinoderms: sea cucumbers, sea urchins, and starfish. The reefs are home to reef sharks, dolphins, and numerous species of mollusks. About 10 to 20 percent of the fish found around the coral reefs are endemic, or found only here.

The Red Sea coast is home to five species of sea turtles: olive ridley (Lepidochelys olivacea), green (Chelonia mydas), loggerhead (Caretta caretta), leatherback (Dermochelys coriacea), and hawksbill (Eretmochelys imbricata). Greens and hawksbills usually forage around the reefs; the greens eat algae and seagrass, while the hawksbills feed on sponges and invertebrates. Leatherbacks, which feed on jellyfish, are usually found farther from the reefs. Both the hawksbill and ridley are critically endangered. However, the other species of sea turtles became threatened or endangered in the twenty-first century.

Migratory birds in the Red Sea coastal zones include swallows, songbirds, stocks, cranes, and birds of prey.

The corallivorous gastropod (Drupellacornus) and other snails of the Drupella genus have caused damage to the Red Sea's ecosystem. These snails and slugs eat coral, primarily of the genera Acropora and Montipora, and spread disease between coral regions.

Fish, phytoplankton, and zooplankton populations in the Red Sea closely resemble those of the Indian Ocean. Common species include the shagreen ray (Leucoraja fullonica) and the black-striped pipefish (Syngnathus abaster), which anchors itself to seagrass by wrapping its tail around it. Endemic species include the tiger bass (Terapon jarbua), which feeds on insects and plant matter; the endangered leopard torpedo (Torpedo panthera), a ray capable of generating electricity as a defense and feeding mechanism; and the great hammerhead shark (Sphyrna mokarran), the largest hammerhead species, with a maximum length of 20 feet (6 meters).

Human and Environmental Threats

The tidal amplitude of the sea is very low, and in the mangrove stands, it is often only about 1 foot (0.3 meter), which helps preserve the stability of the mangrove ecosystems. The roots of the mangroves provide oyster habitats and increase sediment deposits, resulting in sinks for heavy metals. Disrupting the mangrove stands could further contaminate the sea with heavy metals and other pollutants. Mangroves on the Egyptian coast are protected for this reason, and because they help protect the coast from erosion.

Because the land surrounding the Red Sea is arid, there is an elevated demand for freshwater to meet both drinking and industrial demands. There are many desalination plants along the Saudi Arabian coast working to harvest seawater and strip away the salts; however, this results in discharges of warm, highly saline water and treatment chemicals, which puts local fish stocks in jeopardy.

The use of the Red Sea water as a coolant by factories and refineries has a similar effect. For several decades, these effects were localized to the coastal zone immediately surrounding the individual plant, refinery, or factory, but over time, the effects began impacting a larger portion of the sea. Commercial fishing in the sea focuses on lobster, tuna, bonito, herring, sardine, and anchovy.

Although warm water temperatures in other seas are a major cause of coral bleaching, the corals of the southern Red Sea have resisted this threat. In 2020, researchers discovered that the coral reefs in the Red Sea could withstand extreme temperatures. While a 1° F temperature increase will cause bleaching in most corals, those in the Red Sea can withstand a 7° F increase. Scientists began calling this region a thermal refuge for coral survival and theorized that the heat-resistant phenomenon may have occurred because the Red Sea reefs are young. However, by the mid-2020s, bleaching events began increasingly occurring in the Red Sea, including the Gulf of Aqaba. Several organizations aimed to limit the death of the coral reefs in the Red Sea caused by climate change, including the Transnational Red Sea Center (TRSC) and the General Organization for the Conservation of Coral Reefs and Turtles in the Red Sea (SHAMS).

One of the greatest dangers to the Red Sea’s coral is contaminants introduced into the water, particularly because most of the coral is so close to the coast, where there is not only industrial runoff, but also waste from hotels and offshore oil spillage. Hotel waste has been a considerable problem since at least the 1990s, and as tourism increased in countries such as Jordan, even greater amounts of waste entered the sea. Egyptian governments have banned plastic bags in supermarkets in an attempt to reduce the prevalence of the bags in the sea’s waters and reef systems.

Bibliography

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