Marine life refers to the collection of organisms that inhabit Earth's oceans. The World Ocean blankets more than 70 percent of the planet's surface, comprises 99 percent of its living space and hosts almost half of its species. Thus oceans are collectively Earth's largest habitat. According to the first Census of Marine Life, the total number of known marine species is around 250,000.
Marine life is categorized into three basic types: plankton, nekton and benthos. Plankton are organisms that float, relying on wind, currents and waves to move them around. Nekton are large, complex animals that actively and freely swim in water. Benthos are organisms that reside on the seafloor; they either burrow, crawl or are fixed in one place. In addition, many different types of ecosystems can be found throughout the oceans. (Photo: Shutterstock)