The ocean covers 71% of the Earth’s surface, yet  humans have only mapped a small percentage of the  

ocean floor. From shallow coastlines to deep  sea trenches, the ocean floor offers diverse,  

often extreme ecosystems, where many of the  world’s strangest creatures survive and flourish.  

What lives in the ocean’s most  extraordinary oases? What mysterious  

phenomena are hiding at the bottom of the ocean? When you stand on the beach and look across  

the ocean’s surface, you may see nothing but  shimmering water, stretching beyond the horizon;  

but under the surface, the ocean is teeming with  spectacular organisms, thriving inside a wide  

array of complex and delicate ecosystems. Along coastlines, estuaries, and islands,  

marine plants and animals flourish in sunny,  shallow waters. The bright sunlight nurtures  

many vibrant ecosystems, but none as biodiverse as  tropical coral reefs, the rainforests of the sea. 

Coral reefs are living ecosystems, built by  hard, colorful coral. Often mistaken as flora,  

corals are marine invertebrates that grow  in tight clusters along the ocean floor.  

Warm-water corals maintain a symbiotic  relationship with microscopic algae  

called zooxanthellae. Zooxanthellae  live safely inside coral tissue,  

providing their hosts with oxygen and energy.  With the help of zooxanthellae, corals build  

rigid exoskeletons in dynamic formations, which  create a coral reef’s three-dimensional structure. 

Tropical coral reefs support 25% of all marine  life, from the largest rays to the smallest  

microorganisms; but they aren’t the only plentiful  ecosystems found in the ocean’s sunny shallows. 

In temperate and polar climates, up to 40  meters below the surface, dense populations  

of giant kelp, the largest brown algae, grip  the rocky seafloor with branching roots called  

holdfasts. Colonies of giant kelp, anchored to the  ocean floor, form three-dimensional ecosystems,  

which eerily resemble underwater forests. The canopy of a giant kelp forest is rich  

in nutrients. The canopy feeds and  shelters a myriad of organisms,  

like playful sea otters, colorful rockfish, and  barking sea lions. But when the water becomes  

too warm or populations of herbivores grow too  large, this prolific ecosystem can change rapidly. 

Unlike terrestrial forests, which stand tall  for hundreds of years, giant kelp forests  

can disappear and reappear. Warm spells,  tropical storms, and stress from predators,  

like sea urchins, endanger these unique  ecosystems. When in danger, giant kelp  

detaches from the seafloor and drifts along the  current, searching for colder and calmer waters. 

Up to 50 meters below the surface, tropical  and temperate waters house another unusual  

environment: a meadow grown entirely underwater.  Marine meadows are made of seagrasses,  

a group of angiosperms, or flowering plants,  that are completely aquatic. Seagrass meadows  

support a diverse food chain, including manatees,  sea turtles, and many species of crustaceans. 

Beyond the sunny shallows,  and their lush ecosystems,  

the deep sea is a freezing  environment, engulfed in darkness. 

Steep, V-shaped valleys, called submarine  canyons, sink over 1,000 meters below the surface.  

Most submarine canyons are found along  continental margins, often at the mouth of a  

large river. These hyper-productive, nutrient-rich  ecosystems support large populations of megafauna,  

like sharks, swordfish, and giant tuna. While submarine canyons plummet into the deep sea,  

rocky formations, called seamounts, rise from  the darkness. Seamounts are the remnants of  

dormant volcanoes, some of which climb from the  deep sea all the way to the ocean’s surface. 

Seamounts create huge, three-dimensional  ecosystems, providing habitats for a variety  

of marine organisms. Species like sea stars and  deep-sea corals latch on its rocky cliffs, while  

fish and migratory animals, like whales, feed  on numerous species of shellfish and plankton. 

Beyond submarine canyons and undersea mountains,  deep sea trenches, like the Mariana Trench in the  

Pacific Ocean, plummet into a world of darkness  and desolation. The Mariana Trench is the deepest  

place on Earth. This remarkable formation plunges  roughly 11 kilometers below the ocean’s surface,  

where the pressure is 1000 times greater  than atmospheric pressure at sea level. 

For decades, scientists have debated  whether organisms live at the bottom  

of the Mariana Trench. In 1960, the first  manned submarine dove to the Challenger Deep,  

the lowest point in the Mariana Trench. To  their surprise, they discovered living fauna  

thriving in the deepest place on Earth. To survive in dark, barren trenches,  

organisms have taken bizarre  evolutionary turns. Several creatures,  

like sea cucumbers, navigate the deep sea with  specialized, bioluminescent cells. Others,  

like angler fish, use colonies of bioluminescent  bacteria to hunt and lure their prey. 

With limited resources in the deep sea, many  species feed on animal waste, called marine snow,  

that rains down from the shallows. Marine  snow can take weeks to reach the ocean floor,  

creating a storm of white waste, which  looks like an underwater blizzard. 

Occasionally, the bodies  of megafauna, like whales,  

sink to the ocean floor. Whale falls  are big events in the deep sea,  

attracting thousands of scavengers, like  octopi, hagfish, and deep-sea sharks. 

Some deep-sea creatures flourish around undersea  geysers or hydrothermal vents, which erupt in  

streams of mineral-rich seawater, warmed by  magma deep in the Earth’s crust. Hydrothermal  

vents nourish millions of microscopic organisms,  called chemoautotrophic bacteria, which create  

energy in the absence of sunlight. Hydrothermal  vents also support large colonies of mussels,  

worms, and scaly gastropods, creating a diverse  oasis thousands of meters below the surface. 

From the sunlit shallows to the  darkest trenches, the bottom of  

the ocean is an ecological wonderland, home to  extraordinary creatures. To the untrained eye,  

the ocean appears simple and flat, but underneath,  it’s a strange and mysterious world, full of color  

and life. Though we’ve unraveled some of  the ocean’s mysteries, and discovered its  

remarkable diversity, our investigation  of the ocean floor has only just begun. 

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