Marine biology studies plants and animals living in saltwater. Marine biologists work with various species including fish, whales, and microbes. Specialized titles like ichthyologist or cetologist exist for different species
Coral reefs are underwater ecosystems built from colonies of stony corals. Reefs require warm, shallow, clear water and are most common in tropical waters. First appeared 485 million years ago, displacing microbial and sponge reefs. Cover less than 0.1% of world's oceans but support 25% of marine species
Pelagic fish live in ocean or lake waters, between bottom and shore. Marine pelagic environment covers 1,370 million cubic kilometres. Fish range from small forage to large apex predators. Many swim in schools weighing hundreds of tonnes
Atoll is a ring-shaped island with coral rim surrounding a lagoon. Approximately 440 atolls exist worldwide, mostly in Pacific and Indian Oceans. Northernmost atoll is Kure Atoll at 28°25′ N, southernmost atoll is Elizabeth Reef. Lifou (1,146 km²) is largest raised coral atoll, Huvadhu has 255 islands
Seawater has an average salinity of 3.5% (35 g/L). It is denser than fresh water due to dissolved salts. Freezes at about −2°C, with the coldest recorded at −2.6°C. pH ranges between 7.5 and 8.4
Mullets are a family of ray-finned fish found worldwide in coastal waters. Family includes about 78 species in 26 genera. Distinguished by two dorsal fins, triangular mouths, and lack of lateral line. Feed on detritus with muscular stomachs and complex pharynx