Persian Gulf ecosystem

• Category: Marine and Oceanic Biomes.
• Geographic Location: Middle East.
• Summary: The Persian Gulf offers rich biodiversity, but oil and gas extraction threatens the ecosystems there.

The Persian Gulf is a shallow marginal sea located in the northwestern Indian Ocean between southwestern Iran to the east; the Arabian Peninsula to the west and south; and Iran, Iraq and Kuwait to the north. The number of countries in total that surround the Persian Gulf are eight, and include: Iran, Iraq, Kuwait, Saudi Arabia, Bahrain, Qatar, United Arab Emirates, and the Sultanate of Oman. It is sometimes also referred to as the Arabian Gulf by people of the Arab nations here. The Persian Gulf has a maximum length of 614 miles (989 kilometers), a maximum width of 224 miles (362 kilometers), a surface area of 155,964 square miles (251,000 square kilometers), average depth of 164 feet (50 meters), and maximum depth of 295 feet (90 meters).

The Indian Ocean connects to the southeast of the Persian Gulf through the Gulf of Oman via the Straits of Hormuz. The dominant river discharge into the Persian Gulf is from the north, by way of the Shatt al Arab estuary that delineates the border between Iran and Iraq. The Shatt al Arab receives freshwater from the Tigris and Euphrates River system that flow through Iraq, as well as the Karun River that flows from Iran. Other rivers that discharge freshwater into the gulf are exclusively on the Iranian side; these flow down from the Zagros Mountains and include the Mand, Hilleh, and Hendijan Rivers.

Due to the arid climate, the Persian Gulf experiences evaporation rates of some 5–7 feet (1.5–2 meters) per year off of the total surface area, an extreme situation that causes sharp water density and salinity variations in the Gulf. Surface salinity varies between 36 and 41 practical salinity units (PSU) in the summer, with a range of 38-43 PSU in the winter. Surface temperatures here are in the range of 75–93 degrees F (24–34 degrees C) in the summer, and a range of 59–68 degrees F (15–20 degrees C) in the winter. Circulation in the gulf is cyclonic, or counter-clockwise, and deflects freshly entering water from the Indian Ocean initially toward the Iranian coast.

Biodiversity

The arid environment of the Persian Gulf region creates a unique biome. Mangroves here are an ecologically vital marine coastal habitat, one that has been under threat because of human activities and development. The dominant mangrove species of the Persian Gulf is Avicennia marina or grey mangrove, distributed along both the Iranian and Arabian Peninsula coasts. The grey mangroves inhabit the salt flats, or sabkha, adjacent to the coast. The grey mangrove typically is not submerged underwater; the root system consists of pneumatophores or aerial roots.

The less-common Asiatic mangrove, Rhizophora muronata, is more restricted in its distribution along both coasts; it occasionally fringes embayments on either side of the gulf. The Asiatic mangrove has a similar habitat to other species of the genus Rhizophora, which grow submerged roots in seawater. There have been efforts to restore the Asiatic mangrove around the Persian Gulf, such as the UAE Agency for the Environment sponsored program in 2008.

The Persian Gulf biome is home to several charismatic megafauna that are threatened by extinction due to region-wide conflicts, unregulated coastal development and expansion, and accelerated climate change. One of the most widely known is the dugong (Dugong dugon). The dugong is an herbivorous marine mammal belonging to the order Sirenia; its closest relative of the same order is the Atlantic Ocean manatee (Trichechus spp.), whose distribution includes both sides of the Atlantic.

The geographic distribution of the dugong is throughout the Indo-Pacific region spanning from the Persian Gulf to the coasts of Australia. In the Persian Gulf, the dugong can be found off the coasts of Saudi Arabia, Iran, Bahrain, Qatar, and the United Arab Emirates. All these countries recognize that the International Union for Conservation of Nature (IUCN) Red List lists the dugong as vulnerable, and discourages hunting the species.

The dugong lifespan is similar to humans, and they can reach an age of up to 70 years. The adults can reach a length of 9 feet (3 meters) and approximately 881 pounds (400 kilograms). The young reach sexual maturity between the ages of 8 and 18; the female dugong typically bears a single calf once every three years, and rears the calf for 18 months.

The dugong inhabits shallow seagrass beds, which are also their main source of food. When seagrasses are scarce, dugongs may feed on deepwater algae and small invertebrates. Dugongs can hold their breath underwater for about eight minutes, similar to dolphins, but short compared to other marine mammals such as whales (at least 20 minutes and up to 2 hours), seals (70 minutes), or walruses (30 minutes).

Species of whales, dolphins, and porpoise have been recorded in the Persian Gulf. The whale species include Bryde’s whale (Balaenoptera edeni), humpback whale (Magapteraindica), and false killer whale (Pseudorca crassidens). Whales generally have a global distribution, and may have traversed the gulf but gone largely unnoticed due to the lack of a whaling industry here. The same is true in identifying dolphin and porpoise species in the Persian Gulf, which are also a globally cosmopolitan group of mammals.

The speckled dolphin (Sotalia lentiginosa), Indo-Pacific bottle nosed dolphin (Tursiops aduncus), pantropical spotted dolphin (Stenella attenuate), and Asiatic black finless porpoise (Neophocaena phocaenoides) have been documented in the Persian Gulf. The warm and highly productive waters of the Persian Gulf are likely to be appealing as a feeding ground for cetaceans of all sizes. The great abundance of fish and shrimp in the Persian Gulf appears to be able to support and sustain large populations of whales, dolphins and porpoises. However, the activities associated with the oil industry and decades-long armed conflicts may have rendered these species endangered in these waters.

The other charismatic megafauna group is the sea turtle. There are five species of sea turtles identified in the Persian Gulf: loggerhead turtle (Caretta caretta), green sea turtle (Chelonia mydas), hawksbill (Eretmochelys imbricata), olive ridley (Lepidochelys olivacea), and the leatherback sea turtle (Dermochelys coriacea). The IUCN Red List has the green turtles listed as endangered, hawksbill turtles and loggerheads listed as critically endangered, and leatherback turtles as endangered as of 2022. Females of all these species are known to lay their eggs on the shores of islands around the Persian Gulf; many of the known egg-laying sites are protected by the respective governments.

The Persian Gulf hosts over 70 species of migratory birds that use the Gulf as a flight path, rest stop, and feeding grounds as they fly south to winter in Africa, or fly north to summer in northern Eurasia. These include various species of pelicans, cranes, flamingos, and warblers. Most habitats for migratory and endemic birds are in a grave state of degradation due to development.

Coral reefs are the hot spots of diversity in the Persian Gulf biome. Coral reefs and coral species are distributed throughout the shallow waters here, except for the northernmost reaches that are dominated by alluvial mud flats associated with the Shatt al Arab outflow. Generally, a Persian Gulf coral reef consists of several coral species and can go up to 34 species. The dominant hard (scleractinian) coral genus in the Gulf is Acropora spp., which is endemic (found nowhere else); the most common endemic species in the gulf is Acropora arabensis. Other genera include Porites, Siderastrea, Pseudosiderastrea, Favia, and Platygyra. Anthropogenic activities and climatic factors have led to serious degradation of the coral reef habitat—jeopardizing many species of marine reef fishes and invertebrates.

Fishes of the Persian Gulf number over 700 species and over 500 of these are associated with coral reefs. Among important commercial crustacean species of the Persian Gulf are the green tiger prawn (Penaeus semisulcatus) and the penaeid shrimp (Metapenaeus affinis), which uses the southern Iraqi marshes as a nursery ground by traveling up the Shatt al Arab as juveniles and returning to the Persian Gulf upon maturity. There are other brackish water shrimp that are part of the northern Persian Gulf biome that have no commercial value; however, they are important players in the aquatic ecosystem of this extreme environment.

Threats

Human threats to the flora and fauna in this region come from the potential for oil spills, rapid coast development, land-based pollution, oil extraction, and other human-made disasters. As was seen from the BP oil disaster in the Gulf of Mexico, such spills can harm the local environment and wildlife, causing untold damage. Climate change threats to the Persian Gulf region include the potential for food shortages, as acidification of the waters may decrease fish populations. Many people in the region rely upon fish as both a food and income source, and any decreases in the available amount and types of fish can create economic hardship and habitat disruption.

In the 2020s, researchers began studying the Persian Gulf's coral reefs to determine if the coral can withstand high water temperatures. As the temperatures of the world's bodies of water have increasingly risen over the years due to climate change, marine ecosystems have been damaged through events such as extended and widespread coral bleaching. To preserve coral reefs, researchers have shown an increased interest in adaptations and the ability of coral reefs to withstand high temperatures. Through their studies they concluded that the reefs in the Persian Gulf are able to withstand higher temperatures than reefs in other parts of the world. Persian Gulf reefs thrive in water temperatures of up to 96.8 degrees Fahrenheit (36 degrees Celsius) while other reefs cannot handle water temperatures above 89.6 degrees Fahrenheit (32 degrees Celsius). Scientists are not yet sure what makes the reefs in the Persian Gulf so adaptable.

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