All Creatures

Fishes are a diverse group of aquatic vertebrates, comprising both cartilaginous species, such as sharks and rays, and bony species. Sizes range from a few centimetres for small reef inhabitants to pelagic forms that exceed 12 metres (40 ft). Body shapes vary widely, from streamlined fusiform for open-water existence to flattened forms for life on the seabed, or elongated bodies for navigating reef crevices. Colouration often features cryptic patterns for camouflage or bright, distinct patterns used for signalling and warning. Fishes inhabit all depths from the surface to several hundred metres, found across coral reefs, seagrass beds, sandy flats, and the open ocean. Their diets are highly varied, including algal grazers, plankton feeders, and predators of invertebrates and other fish. Many species detect water movements using a lateral line system, a row of sensory pores along the body. Cartilaginous species also employ electroreception through ampullae of Lorenzini, sensing electrical fields generated by other organisms. Behaviourally, many species exhibit complex social patterns, such as schooling, or engage in symbiotic relationships.

Invertebrates are animals that lack a vertebral column. This diverse group includes soft-bodied organisms such as anemones and jellyfish, as well as those protected by shells or exoskeletons, like molluscs and crustaceans. Adult sizes vary widely, from a few millimetres in some worms and small crustaceans to several metres; large sessile forms like sponges and gorgonian corals can exceed 3 metres (10 ft) in height or spread. They inhabit a broad range of marine environments, from shallow intertidal zones to mesophotic reefs at depths over 100 m (330 ft). Many species contribute to the structural framework of coral reefs, forming the matrix of the ecosystem. Others burrow into sediments or live symbiotically with fish and other invertebrates. Feeding strategies are diverse, encompassing filter feeding, grazing on algae, and active predation.

Marine mammals are air-breathing, warm-blooded vertebrates that give live birth and nurse their young. They possess streamlined, fusiform bodies, with forelimbs modified into pectoral flippers and horizontal tail flukes for propulsion. A thick blubber layer insulates most species. Cetaceans, comprising dolphins and whales, breathe through a single or double blowhole located on top of the head. Dugongs, the Red Sea's only sirenian, breathe through nostrils positioned on the snout. Body lengths vary widely, from common dolphins at 1.7-2.4 m (5.6-7.9 ft) to large whale species exceeding 15 m (49 ft). Dugongs typically reach up to 3 m (9.8 ft) in length and weigh over 400 kg (880 lb). Most species display countershading, with darker dorsal surfaces and lighter ventral surfaces. These animals inhabit open water, reef slopes, and along drop-offs, observed from the surface down to several hundred meters. Dugongs are found exclusively in shallow, sheltered bays with extensive seagrass beds, typically at depths of 1-10 m (3-33 ft). Cetaceans are primarily carnivorous, feeding on fish and squid, often foraging cooperatively in social pods. Dugongs are strictly herbivorous, grazing on seagrass, and typically occur singly or in small groups. Dolphin species are commonly encountered by divers, sometimes displaying curious behaviour, while larger whales are observed less frequently.

Marine reptiles breathe air and have scaly skin. In the Red Sea, only sea turtles are encountered; sea snakes are absent, likely restricted by cold upwellings off southern Arabia. Sea turtles possess a streamlined body with a bony or leathery carapace, typically measuring 60-120 cm (24-47 in) long. Their four strong, paddle-like flippers cannot be withdrawn into the shell, and their bodies are flattened dorsoventrally, adapting them for aquatic life. These reptiles frequent shallow reef flats, seagrass beds, and deeper reef slopes, often resting under ledges or in caves. They must surface regularly to breathe, though they can remain submerged for extended periods. Green turtles (Chelonia mydas) graze on seagrass and algae, while Hawksbill turtles (Eretmochelys imbricata) primarily consume sponges, making both common sightings for divers. Banded snake-like animals encountered are typically snake eels or banded morays.

Sea plants are diverse photosynthetic organisms encountered in marine environments, encompassing various forms of multicellular algae, known as seaweeds, alongside true flowering plants like seagrasses and mangroves. Seaweeds typically attach to hard substrates, displaying forms that range from fine filaments to broad, flat blades or bushy structures. Their colours vary through green, brown, and red, depending on their photosynthetic pigments, and they can be found from the intertidal zone down to depths of 50-70 metres where light penetration allows. Seagrasses form dense green meadows on soft sandy or muddy bottoms, identified by their strap-like blades, which usually measure 10-60 cm (4-24 in) in length. Mangroves are woody trees that grow several metres tall, distinguished by their prominent aerial root systems. Seagrasses thrive in shallow, sheltered waters, typically within 30 metres (100 feet) depth, forming extensive beds. Mangroves grow exclusively in the intertidal zones of protected Red Sea lagoons and bays. These organisms all produce their own food through photosynthesis, converting sunlight into energy. They collectively create nursery grounds, provide shelter for numerous marine invertebrates and fish, and stabilize sediments in coastal areas.