Open water habitats


Vast numbers of mostly microscopic plants and animals drift passively in the water, the plankton. They are divided into two groups: plants, or phytoplankton (67-72), and animals, or zooplankton (73-80). The phytoplankton, as all true plants, use light energy captured by chlorophyll molecules for the process of photosynthesis, converting dissolved carbon dioxide and water into carbohydrates and thereby providing the base for the open water food chains. They exist in vast numbers and have a rapid reproductive cycle.

Many species of phytoplankton, mainly diatoms (67-69) and dinoflagellates (70-72) have now been identified. The diatoms are single-celled green plants with skeletons made from silicon; the dinoflagellates have cellulose walls like plants and move about with the help of long beating threads (flagella). Most are very tiny, less than 0.01 mm across, so you can swallow many thousands in a mouthful of seawater!

Zooplankton are consumers, many are one-celled animals, protozoa (73), propelled by flagella or cilia (many small beating hairs) feeding on the phytoplankton or dead organic material. Many larger multicellular animals, which also drift with the ocean currents, are also important components of the zooplankton. Examples include small worms, tiny molluscs, jellyfish (77), copepods (74) and the larval stages of many fish (78) and crustacean (80) species. Arrow worms (chaetognaths, 76) are predators in the plankton.

Many fish species will feed on the zooplankton such as some damselfishes (81), small silversides (82), and sardines. These are themselves preyed upon by carnivores such as needle fish, squid, tuna, jacks (83) and barracuda (84). Sharks, dolphins, sea snakes and seabirds are the 'top' predators being at the end of the food chain.

Sharks found within the Sanctuary and around the offshore islands include the blacktip reef shark (85) and the hammerhead (86).

Open water sea birds include the red-necked phalarope (87) and feeding flocks of the endemic Socotra cormorant (88). Three colonies of these cormorants with a total of 30,000 breeding pairs were found in the Saudi Arabian section of the Gulf in 1994. These birds are extremely sensitive to disturbance during their breeding season and consequently their colonies are only found on remote islands.

Fishing plays a very important role in this area and the reduction in abundance and diversity of certain species by fishing is of major concern. Popular species such as rabbit fish and groupers may be declining. Commercially important populations of shrimp are caught in the bays and north of Abu Ali.

Sea snakes are not aggressive and do not normally attack people. You may swim without fear. However, if specimens are found washed up on the beach during the cold winter months they may appear dead when in fact they are still alive.

Three species of marine mammals are relatively common: the humpback dolphin (91) which may prefer coastal waters, the bottlenose (90) and the common dolphin (89), the latter being the species which usually rides the bow waves of the boats.