Animals and plants that live in saltwater biomes feature adaptations designed to prevent osmosis from equalizing the salt concentration throughout their bodies while remaining capable of absorbing oxygen from the water. Animals do this through specialized kidneys and gills, while plants do this directly through their cell walls.
The marine biome is the largest saltwater biome in the world, according to Kids Do Ecology. It covers 70 percent of the planet's surface and contains millions of different species of plants and animals. All these creatures have adapted to life at sea by developing organs that maintain homeostasis in their bodies. Simple animals such as worms and anemones absorb oxygen directly through their skin, while biologically complex animals make use of gills or even specialized lungs to take in oxygen. Complex animals in marine environments tend to feature compressible air spaces inside their bodies, making it possible to survive in the enormous pressure of a saltwater environment, as explained by the MarineBio Conversation Society.
Saltwater plants such as seaweed and kelp are so different from terrestrial plants that they are not plants in a biological sense. Instead, scientists classify them as protists. This is because these plants absorb nutrients from the surrounding water without using an internal vascular system, as OceanLink explains.