The Arabian Gulf is an enclosed sea and is among the most challenging marine environment for marine life, yet it hosts an incredible variety of creatures and different marine habitats.
It is a fairly “new” sea, as it was completely dried out until the end of the Last Glacial Maximum about 10,000 years ago, when the sea level rose and the Indian Ocean flooded through the narrow Straits of Hormuz into the once plains of the Tigris and Euphrates rivers (Teller et al., 2000). All the marine species present in the Gulf today migrated from the Indian Ocean, once the new marine environment was settled.
Today it is a shallow basin with an average depth of 35 metres to a maximum depth of 90 metres. Water temperatures and salinity show high seasonal fluctuation, making the Gulf a unique environment that requires extreme adaptation from all the resident marine life. The water temperature during summer (May to October) can reach up to 35oC, and over winter (September to April) can drop to as low as 15 oC. Salinity is between 40-50 ppm, this is exceptionally high if compared to the average ocean salinity of 34.7 ppm.
The Gulf offers a variety of different marine environments from vast intertidal and sub-tidal shallow areas, mangrove forests, coral reefs, sea grass beds and pelagic habitats.
Intertidal and sub-tidal shallow areas
Due to the gradual slope that characterises most of the Gulf and the range of tides, the intertidal or littoral zones represent an important part of the local marine environment. This habitat is still one of the most vulnerable because human interaction and climate change. Naturally they are subjected to the highest shift in environmental conditions between summer and winter. Most of the littoral areas are sandy but you can also find lagoons, rocky platforms and pools, and muddy areas. These areas are, generally of strategic importance for many marine species and birds that shelter during breeding season.
Mangroves are extremely important for the marine biodiversity. Not only as they act as the best antidote for coastline erosion, but they also represent an unique ecosystem that provide suitable habitat and safe breeding grounds for many fish species, such as snapper, grunt fish, sea bream, shrimps and crabs. It is also an important habitat for many species of birds and marine turtles. In UAE mangroves are a significant part of the local marine environment and can be found on both the east and west coast of the country, although the majority is located in Abu Dhabi. Main threats for the mangroves are pollution, coastal development, sedimentation, change in tidal flow and human related activities.
Despite the general misconception that corals are plants, as they do not move, they are actually animals, organised in colonies of polyps that in the early stage of their life actually move across oceans. Coral reefs play a crucial role in maintaining the marine biodiversity, hosting a wide variety of small and big marine organisms, from tiny molluscs to reef sharks. Although the Gulf waters represent an extreme environment for the corals survival, due to the extreme salinity and temperature range and the level of suspended sediments, a wide variety of soft and hard corals can be found. Today corals worldwide are facing serious threats from climate change, human related activities and pollution.
Sea Grass Beds:
Sea grass are mainly submerged flowering vascular plants that prefer soft bottom sediment in shallow areas. The Gulf provides an ideal habitat for sea grass although the extreme shifts in water temperature and salinity represents a challenge for its survival. Out of 50 species of sea grass worldwide, in the Gulf only three are represented and they are considered among the most tolerant to environmental shifts. The sea grass areas play an important role in the marine ecosystem, providing habitat stabilization, nutrient recycling, and shelter form marine species. In the UAE sea grass beds are the favourite habitat for dugong, a large marine mammal, and green turtles, as the both feed on it.
As the Gulf is a shallow body of water with a maximum depth of 90 meters, most of the pelagic areas are considered epipelagic, as the depth still allows enough light for the photosyntesis. There is not much data on the pelagic areas of the Gulf but reports of large fish and sharks such as sunfish, tuna, kingfish, whale shark and bull shark are common. Several cetacean species have also been reported such as Bryde’s and humpback whales, bottlenose, common and spinner dolphins, false killer whale and killer whales. Research is currently being conducted on whale sharks in the Gulf.