The oceans now cover 71 per cent of the world and over 90 per cent of its habitable living space. They provide vital nutrients, dissolved gases, and mineral salts, and are rich in oxygen with their surface bathed in an endless supply of sunlight. ‘Marine web of life’ provides an introduction to marine biology. Each of the six kingdoms into which we classify life is well represented in the marine realm. Different species play their own unique role in the cycles, complex webs, and food chains of the oceans. The different biozones and habitats of the oceans are described along with the world of plankton, the range of movement styles underwater, feeding strategies, reproduction at sea, and the deep-ocean habitat.