Chapter 17 sec3 Marine Ecosystems Key concepts

Marine ecosystems are shaped by abiotic factors. Two important factors are water depth and amount of sunlight that passes through water. Sunlight does not reach deeper than 200 m.

Water temperature is another important abiotic factor in the oceans. Ocean water becomes colder as it becomes deeper. However, the temperature change is not gradual.

Because the water in the surface zone is heated by the sun, it is much warmer than the rest of the ocean. Temperatures in the surface zone vary with latitude. Surface-zone temperatures are higher closer to the equator and lower closer to the poles.

Animals that live in different marine ecosystems are adapted to different temperatures. Fish that live near the poles have a special chemical in their blood that prevents them from freezing. In contrast, fish that live in coral reefs need warm water to survive.

Most marine organisms live in the warm waters of the surface zone. Some animals, such as whales, migrate from cold, polar areas to warm areas in order to reproduce. Water temperature may affect whether some animals can eat. Sudden changes in temperature can cause animal death.

The ocean can be divided into zones based on distance from shore, water depth, amount of sunlight in the zone, and water temperature. The intertidal zone is the zone where the ocean meets the shore. Organisms in this zone are adapted to survive exposure to air and the crashing of waves.

The neritic zone is farther from shore. In this zone, the water becomes deeper as the ocean floor starts to slope downward. Corals and other producers thrive in this warm, sunny zone.

In the oceanic zone, the sea floor drops sharply. This zone extends from the surface to the deep waters of the open ocean. Phytoplankton live near the sunny surface.

Consumers such as fishes, whales, and sharks live in the oceanic zone. Some of these animals live deep in the zone, where sunlight does not reach. These animals feed on each other, and on material that sinks from surface waters.

The abyssal zone is the ocean floor. It does not receive any sunlight. This zone is also very cold. Fishes, worms, and crabs have special adaptations for living in this zone.

Many of these consumers feed on material that sinks from above. Some organisms, such as angler fish, eat smaller fishes. Decomposers such as bacteria help break down organisms.

Intertidal Ecosystems Different intertidal ecosystems include mudflats, sandy beaches, and rocky shores. Intertidal organisms are able to live both in and out of water. The organisms that live in mudflats or beaches often burrow into the sediment.

Consumers that live in these areas are worms, crabs, clams, and shorebirds. On rocky shores, animals have adaptations to keep from being swept away by crashing waves.

Seaweeds use rootlike structures called holdfasts to attach to rocks. Other organisms, such as barnacles, attach themselves to rocks with a special cement. Sea stars feed on these organisms.

Estuaries An area where salt water from the ocean flows into the mouth of a stream or river is called an estuary. In estuaries, fresh water and salt water are always mixing. Therefore, salt concentration is always changing.

Organisms in estuaries must be able to survive changing concentrations of salt. High nutrient levels from the rivers that spill into the estuary support large numbers of producers, such as algae. The algae support many consumers.

Coral reefs are named for corals, the animals that form these reefs. Most corals are made up of many individuals living in a group or colony. Algae live in the tissues of coral, and provide the coral with nutrients.

Most coral reefs are found in the warm, shallow areas of the neritic zone. The structure of a coral reef is mainly based on the skeletons of stony corals. These skeletons are made of calcium carbonate.

As corals grow and die, their skeletons build up and form a reef. This reef provides a home for algae and many marine animals. Coral reef organisms include fishes, sponges, sea stars, and sea urchins.

Kelp Forests Kelp forests are found in cold, shallow areas of the neritic zone. Kelp are large brown algae that grow well in nutrient-rich areas, such as areas along the coast of California. Some kelp can be more than 33 m long.

Their tops can be seen floating on the ocean’s surface. Many organisms, such as sea otters, fishes, crabs, and sea urchins, are found in kelp forests. Sea urchins are primary consumers that eat algae growing on rocks.

Sea otters are secondary consumers that eat many organisms, including sea urchins. Sometimes, sea otters wrap themselves in kelp to stay afloat while they take a nap.

Deep-Sea Hydrothermal Vents Deep-sea hydrothermal vents are found in the abyssal zone. These vents release toxic chemicals and water with temperatures as hot as 360°C. Vent worms and crabs live near these vents.

Bacteria live in the bodies of vent worms. These bacteria make food from the chemicals released from the vents. The extra food is transferred to the worm.

These bacteria are considered to be producers because they can make their own food. Instead of using the sun’s energy, they use the energy from Earth’s interior to make food. The mutualistic relationship between bacteria and vent worms is similar to the relationship between some algae and coral.

The Sargasso Sea The ecosystem called the Sargasso Sea is found only in the middle of the Atlantic Ocean. Floating rafts of algae called sargassums make up the base of this ecosystem. Sargassums float because parts of these algae are filled with air.

Most animals that live in this ecosystem are omnivores and can eat many different kinds of organisms throughout the year. Some of the animals, like the Sargasso fish, are the same color as the sargassums. Its color helps the fish hide from predators.

Polar Ice The Arctic Ocean and ocean around Antarctica make up another kind of marine ecosystem. These icy waters are rich in nutrients and support large numbers of phytoplankton.

In turn, these phytoplankton support other organisms, such as fishes and krill. Krill are tiny shrimplike organisms that some whales rely on for food. Seals feed on fishes that eat krill and are, in turn, eaten by polar bears.