Open ocean

How species adapt

Life in the open waters is divided into two groups: drifters (plankton) and swimmers (nekton).

Drifters and swimmers

Plankton are carried mainly by currents. A diverse group, they range from microscopic plants and animals (some animals, such as octopuses, begin life as plankton) to large jellies. Nekton travel great distances to find food. This group includes fishes, whales, sea turtles, and squid. With very different lifestyles, both groups are well adapted for life in the open sea.

Sunlight means food

Because sunlight and the richest food supplies are in the surface waters, plants, and plankton eaters must stay near the surface to survive. Some microscopic plants and animals slow their rates of sinking to stay close to the surface. Many species of fish have air-filled swim bladders to support them in the water. Others, such as ocean sunfish and whales, rely on layers of fat beneath their skin to keep them buoyant.  

Protection from predators

Without places to hide, animals of the open sea must find ways to avoid predators. Many fishes, like sardines and anchovies, school for protection. There’s safety in large numbers since tightly schooling fish can look like an intimidating larger creature. Schooling can also confuse predators trying to catch a single fish in a large group. 

The sea as camouflage

Some animals, like jellies, have virtually invisible gelatinous bodies. Others, like tuna, sharks, dolphins, and sea turtles, rely on countershading (light on the bottom, dark on top) to make them less visible. Viewed from above, their bodies blend in with the ocean depths. From below, their light undersides blend with bright surface waters.

How this habitat changes

Changes in ocean circulation and water temperature significantly affect microscopic plants called phytoplankton that form the basis of the food chain in the open sea. Whales, shrimp, snails, jellyfish, and many fishes depend on phytoplankton as a primary food source.

Migration

As waters warm, phytoplankton die or migrate to cooler areas, affecting the fish and other marine life that depend on plankton for food. Animals adapt by changing their migration and breeding patterns, which in turn affects other animals in the food web.

Overfishing

Commercial fishing also changes this habitat, creating imbalances that affect all marine life. Overfishing occurs when animals are taken from the ocean faster than they can reproduce. Today, more than 170 billion pounds (77 kg) of marine life is removed from the world’s oceans each year. 

Commercial fishing methods often result in bycatch—the unintentional capture and destruction of additional species. Many sharks and rays are killed and tossed aside as bycatch, for example.

Things to look for and notice

Large “slicks” of phytoplankton are found in patches near the ocean’s surface. Tiny but present in unimaginable numbers, phytoplankton support virtually all life in the ocean.

Watch for marine mammals such as dolphins, whales, seals coming to the surface to breathe air—and to have a look around. 

You might also spot seabirds such as the common murre, congregating in large numbers on the surface in open waters.

How to protect this habitat

People are having a greater impact on the ocean’s inhabitants and water quality. We can help keep seas healthy by supporting effective environmental legislation, respecting and obeying fishing regulations, keeping trash off of our beaches, and safely disposing of toxic chemicals.

Buy sustainable seafood

Choose seafood that is fished or farmed in ways that support a healthy ocean. Learn more at Seafood Watch.

Reduce your plastic use

Plastic bags kill sea turtles, molas, rays and other animals who swallow them, believing they’re jellies. Carry reusable shopping bags with you to the store, reuse the plastic bags you do have, and pick up any plastic trash you find blowing around outdoors. Learn more about how you can help end plastic pollution.