Lesson Objectives

• Describe the different types of ocean organisms.
• Describe the interactions among different ocean organisms.

Vocabulary

• chemosynthesis
• hydrothermal vent
• invertebrate
• phytoplankton
• plankton
• primary productivity
• reef
• vertebrate
• zooplankton

Introduction

Oceans are a harsh placed to live. In the intertidal zone, conditions change rapidly as water covers and uncovers the region and waves pound on the rocks. Most of the environments at sea are cold and at just about any depth below the surface the pressure is very high. Beyond the photic zone, the ocean is entirely black. Organisms have adapted to these conditions in many interesting and effective ways. The size and variety of different habitats means that the oceans are home to a large portion of all life on Earth.

Types of Ocean Organisms

The smallest and largest animals on Earth live in the oceans. Why do you think the oceans can support large animals?

Marine animals breathe air or extract oxygen from the water. Some float on the surface and others dive into the ocean’s depths. There are animals that eat other animals, and plants generate food from sunlight. A few bizarre creatures break down chemicals to make food! The following section divides ocean life into seven basic groups.

Plankton

Plankton are organisms that cannot swim but that float along with the current. The word “plankton” comes from the Greek for wanderer. Most plankton are microscopic, but some are visible to the naked eye (Figure below).

Phytoplankton are tiny plants that make food by photosynthesis. Because they need sunlight, phytoplankton live in the photic zone. Phytoplankton are responsible for about half of the total primary productivity (food energy) on Earth. Like other plants, phytoplankton release oxygen as a waste product.

A video of a research vessel sampling plankton is seen here: http://www.youtube.com/watch?v=mQG4zAoh6xc.

Zooplankton, or animal plankton, eat phytoplankton as their source of food (Figure below). Some zooplankton live as plankton all their lives and others are juvenile forms of animals that will attach to the bottom as adults. Some small invertebrates live as zooplankton.

Plants and Algae

The few true plants found in the oceans include salt marsh grasses and mangrove trees. Although they are not true plants, large algae, which are called seaweed, also use photosynthesis to make food. Plants and seaweeds are found in the neritic zone where the light they need penetrates so that they can photosynthesize (Figure below).

Marine Invertebrates

The variety and number of invertebrates, animals without a backbone, is truly remarkable (Figure below). Marine invertebrates include sea slugs, sea anemones, starfish, octopi, clams, sponges, sea worms, crabs, and lobsters. Most of these animals are found close to the shore, but they can be found throughout the ocean.

KQED: Amazing Jellies

Jellies are otherworldly creatures that glow in the dark, without brains or bones, some more than 100 feet long. Along with many other ocean areas, they live just off California’s coast. Learn more at: http://science.kqed.org/quest/video/amazing-jellies/.

Fish

Fish are vertebrates; they have a backbone. What are some of the features fish have that allows them to live in the oceans? All fish have most or all of these traits.

• Fins with which to move and steer.
• Scales for protection.
• Gills for extracting oxygen from the water.
• A swim bladder that lets them rise and sink to different depths.
• Ectothermy (cold-bloodedness) so that their bodies are the same temperature as the surrounding water.
• Bioluminescence: light created from a chemical reaction that can attract prey or mates in the dark ocean.

Included among the fish are sardines, salmon, and eels, as well as the sharks and rays (which lack swim bladders) (Figure below).

Reptiles

Only a few types of reptiles live in the oceans and they live in warm water. Why are reptiles so restricted in their ability to live in the sea? Sea turtles, sea snakes, saltwater crocodiles, and marine iguana that are found only at the Galapagos Islands sum up the marine reptile groups (Figure below). Sea snakes bear live young in the ocean, but turtles, crocodiles, and marine iguanas all lay their eggs on land.

Seabirds

Many types of birds are adapted to living in the sea or on the shore. A few are shown: (Figure below).

Marine Mammals

What are the common traits of mammals? Mammals are endothermic (warm-blooded) vertebrates that give birth to live young; feed them with milk; and have hair, ears, and a jaw bone with teeth.

What traits might mammals have to be adapted to life in the ocean?

• For swimming: streamlined bodies, slippery skin or hair, fins.
• For warmth: Fur, fat, high metabolic rate, small surface area to volume, specialized blood system.
• For salinity: kidneys that excrete salt, impervious skin.

The five types of marine mammals are pictured here: (Figure below).

KQED: Into the Deep with Elephant Seals

Thousands of northern elephant seals — some weighing up to 4,500 pounds — make an annual migration to breed each winter at Año Nuevo State Reserve in California. Marine biologists are using high-tech tools to explore the secrets of these amazing creatures. Learn more at: http://science.kqed.org/quest/video/into-the-deep-with-elephant-seals/.

Interactions Among Ocean Organisms

The previous section briefly discussed the adaptations different types of organisms have to live in the ocean. A look at a few of the different habitats organisms live in can focus even more on these important adaptations.

The Intertidal

A great abundance of life is found in the intertidal zone (Figure below). High energy waves pound the organisms that live in this zone and so they must be adapted to pounding waves and exposure to air during low tides. Hard shells protect from pounding waves and also protect against drying out when the animal is above water. Strong attachments keep the animals anchored to the rock.

In a tide pool, as in the photo, what organisms are found where and what specific adaptations do they have to that zone? The mussels on the top left have hard shells for protection and to prevent drying because they are often not covered by water. The sea anemones in the lower right are more often submerged and have strong attachments but can close during low tides.

Many young organisms get their start in estuaries and so they must be adapted to rapid shifts in salinity.

Reefs

Corals and other animals deposit calcium carbonate to create rock reefs near the shore. Coral reefs are the “rainforests of the oceans” with a tremendous amount of species diversity (Figure below).

Reefs can form interesting shapes in the oceans. Remember that hot spots create volcanoes on the seafloor. If these volcanoes rise above sea level to become islands, and if they occur in tropical waters, coral reefs will form on them. Since the volcanoes are cones, the reef forms in a circle around the volcano. As the volcano comes off the hot spot, the crust cools. The volcano subsides and then begins to erode away (Figure below).

Eventually, all that is left is a reef island called an atoll. A lagoon is found inside the reef (Figure below).

Coral reef are near shore and so are subject to pollution from land. The coral animals are very sensitive to temperature and reefs around the world are stressed from rising ocean temperatures.

Some videos about threats to coral reefs are found at: National Geographic Videos, Environment Video, Threats to Animals, http://video.nationalgeographic.com/video/player/environment/.

• Coral Reefs
• Belize’s Coral Reef

Oceanic Zone

The open ocean is a vast area. Food either washes down from the land or is created by photosynthesizing plankton. Zooplankton and larger animals feed on the phytoplankton and on each other. Larger animals such as whales and giant groupers may live their entire lives in the open water.

How do fish survive in the deepest ocean? The few species that live in the greatest depths are very specialized (Figure below). Since it’s rare to find a meal, the fish use very little energy; they move very little, breathe slowly, have minimal bone structure and a slow metabolism. These fish are very small. To maximize the chance of getting a meal, some species may have jaws that unhinge to accept a larger fish or backward-folding teeth to keep prey from escaping.

Many ocean-related videos are found in National Geographic Videos, Environment Video, Habitat, Ocean section: http://video.nationalgeographic.com/video/player/environment/. Just a few are listed below.

• How we can know what lives in the ocean is in “Deep-Sea Robo Help”
• Some of the results of the Census of Marine Life have been released and are discussed in “Record-Breaking Sea-Creature Surveys Released”
• Bioluminescence is common in the oceans and seen in “Why Deep Sea Creatures Glow”

Hydrothermal Vents

At mid-ocean ridges at hydrothermal vents, bacteria that use chemosynthesis for food energy are the base of a unique ecosystem (Figure below). This ecosystem is entirely separate from the photosynthesis at the surface. Shrimp, clams, fish, and giant tube worms have been found in these extreme places.

A video explaining hydrothermal vents with good footage is seen here: http://www.youtube.com/watch?v=rFHtVRKoaUM.

Lesson Summaries

• The oceans have a tremendous diversity of life: bacteria, plankton, invertebrates, and vertebrates, which include fish, reptiles, seabirds, and mammals.
• Photosynthesis and chemosynthesis create food energy in two very different ways.
• Plankton are tiny freely floating plants (phytoplankton) or animals (zooplankton).
• All marine organisms must be specialized for the harsh conditions of the ocean environment in which they live.

Review Questions

1. What is an invertebrate? Name two types.

2. What is the role of phytoplankton in ocean ecosystems?

3. If fish require oxygen to live, why can’t they survive on land?

4. Are polar bears marine mammals or land animals like all other bears. What is your opinion?

5. What are four major habitats of ocean organisms?

6. Describe adaptations that an organism that lives in a reef might have. How might these adaptations be different from an organism that lives in the open ocean?

7. Describe the importance of maintaining the ocean ecosystems.

Points to Consider

• How does the ocean interact with the atmosphere?
• How is energy transferred around the planet and how does this affect life on Earth?
• What would be the effect of pollution on the oceans?