EnchantedLearning.com Biomes - Habitats

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The middle layer of the world's oceans receives only faint, filtered sunlight during the daytime. This is because the seawater absorbs the sunlight. This barely-lit ocean layer is called the twilight zone or the disphotic zone (disphotic means "poorly lit" in Greek) or the mesopelagic zone (mesopelagic means "middle sea"). This zone appears deep blue to black in color. The depth of this zone depends on the clarity or murkiness of the water. In clear water, the disphotic zone can begin at depths up to 600 feet; in murky water, it can start at only 50 feet deep. It is usually begins somewhere between these two extremes. The disphotic zone extends to about 3,300 feet (about 1,000 m) deep (this is where the aphotic zone begins). On average, this zone extends from 660 to 3,300 feet (200 to 1,000 m).

In the disphotic zone, there is enough light to see during the day, but not enough light for photosynthesis to take place, so no plants live in this zone. The amout of light decreases with depth. Because of this, food is not abundant.

The water in the disphotic zone is cold (the temperature ranges from 41 to 39 degrees F) and decreases with depth. The pressure is high -- it can be up to 1,470 psi (pounds per square inch) and increases with depth. The amount of dissolved oxygen in the water is less than in the sunlit zone.

The undersea explorers William Beebe and Otis Barton were the first people to travel to this remote zone (in a bathyscaphe) and see the animal life in it. Robert Ballard later explored it more extensively.

Animals:
The animals that live in the disphotic zone are adapted to life in near darkness, cold water and high pressure. Many of the animals in this zone have large eyes, helping them see in the nearly dark waters. Most are small, dark and thin (to help camouflage them). Many have large teeth and jaws.

Bioluminescence: Many of the animals in the disphotic zone are bioluminescent; they can make their own light. Some bioluminescing animals have special organs that produce light by a chemical reaction; other bioluminescing aniamls have glowing bacteria that live on them. Most bioluminesscing organs called photophores give off an eerie blue-green light. A rare exception is the Malacosteidae or Loosejaw fish, who produce a red light for intraspecies communication (red is invisible to most other deep-sea marine organisms, who see mainly blues and greens). Animals use their light to help them find food, to help them find mates, and/or to confuse predators (they do this by camouflaging themselves or distracting predators).

Counterillumination is a method of camouflage. Lght produced on the underside of bioluminescing animals can help the animal "disappear" from predators that are below it. The top part of the animal is not lit; to animals looking down from above the prey, the prey animal is virtually invisible since its dark silhouette appears against a black background.

Some animals (like deep-sea shrimp) regurgitate bioluminescing fluid when attacked - this confuses and distracts the attacker.

Diet: Animals in this zone feed on plant matter and algae that fall into this zone from the euphotic zone (the well-lit zone above the disphotic zone), animals that stray into this twilight zone, and each other. Animals in the disphotic zone are filter feeders, grazers, and predators. Some animals migrate vertically (up and down) in order to feed upon the abundant life in the bright zone above them. Most of the animals that eat other animals in this zone do not chase their prey; they lure the prey to them or simply wait for the prey to come to them. Some predators lure their prey with bioluminescent barbels (fleshy projections near the mouth) that look like small animals.

Examples of disphotic zone animals include algae, coelacanths, copepods, crabs and other crustaceans, ctenophores, dinoflagellates, dragonfish, fangtooth, gulper eel, hatchet fish, hydrozoans, medusas, lantern fish, snipe eels, some octopuses, mid-water jellyfish (Cnidarians), plankton, polychaetes, radiolarians, siphonophore, rattalk fish, sea dragons, some shrimp, some squid, viperfish and many worms (including tubeworms and segmented worms).

Twilight Ocean (Disphotic) Zone Animal Printouts:

Angelshark A bottom-dwelling, relatively harmless shark with a flattened body and a blunt snout.

Brittle Star A bottom-dwelling marine invertebrate with long, spiny arms.

Coelacanth The Coelacanth (pronounced SEE-la-canth) is a primitive lobe-finned fish that was thought to have been extinct for millions of years, but a living Coelacanth was caught in the Indian Ocean off the coast of South Africa in 1938.

Clam Burrowing bivalves with a soft body.

Copepod Copepods are tiny crustaceans from fresh and salt water.

Crab A crab is an animal with a shell. It has eyes on stalks on its head.

Cuttlefish Cuttlefish are cephalopods with relatively short legs, a fin along the entire mantle, and an internal cuttlebone.

Eels Information and printouts on these primitive fish that go through metamorphosis.

Echinoderms Spiny-skinned, bottom-dwelling marine invertebrates with five-fold symmetry.

Fiddler Crab: Label Me! Printout Label the external anatomy of the fiddler crab. Answers

Gastropods Gastropods are a class of mollusks with a single (or absent) shell and a muscular foot.

Gray Whale The gray whale is baleen whale that is a bottom feeder; it migrates very long distances each year.

Greenland Shark A large, slow-swimming shark with glow-in-the-dark eyes.

Hatchetfish Hatchetfish are oddly-shaped fish from South and Central America.

Hermit Crab Hermit crabs are crabs that lack a hard shell; they use a discarded shell for protection.

Hermit Crab Diagram: Label Me! Label the external anatomy of the hermit crab both in its shell and out of it. Answers

Horseshoe Crab The horseshoe crab is a hard-shelled animal that lives in warm coastal waters on the sea floor.

Jellyfish Jellyfish are animals that have stinging tentacles. Or go to an unlabeled version.

John Dory John Dory is a spiny fish with a black spot on its side. It lives near the sea floor, when it is from 15-120 ft (5-360 m) deep.

Krill Small crustaceans that are eaten by many animals, including baleen whales.

Limpet The limpet is a marine invertebrate (a gastropod) with a flattened, cone-shaped shell.

Lobster A hard-shelled marine invertebrate with 10 jointed legs.

Mollusks Mollusks are soft-bodied invertebrates. Some mollusks include the octopus, squid, clam, snail, slug, and tusk shells.

Octopus Octopi have eight legs and live on the sea floor.

Octopus Shape Book A short book about the octopus to print, with pages on octopus anatomy, a connect-the-dot activity, a page on the most poisonous octopus, octopus facts, and octopus questions.

Oyster The oyster is a bivalve, a soft-bodied marine animal that is protected by two hard shells.

Plankton Plankton are tiny organisms that float in the seas and other bodies of water.

Pufferfish Also called blowfish and fugu, this poisonous fish can swallow water to double its size.

Purple Sea Urchin A spiny, globular animal that lives on the ocean floor off the western coast of North America.

Sand Dollar Sand Dollars are echinoderms, disk-shaped spiny-skinned sea bed animals that have 5-part radial symmetry.

Scallop Scallops are bivalves, shelled animals that live on the ocean floor.

Sea Anemone A predatory animal that looks like a flower and lives on the ocean floor.

Sea Cucumber Sea cucumbers are cylinder-shaped echinoderms.

Sea Star Sea stars, another name for starfish, are animals that live on the ocean floor.

Sea Urchin A spiny, globular animal that lives on the ocean floor.

Shrimp Shrimp are small, bottom-dwelling crustaceans with a translucent exoskeleton.

Snail A soft-bodied animal with a hard, protective shell.

Sperm Whale The Sperm whale is the largest toothed whale; it is over 50 feet long. It eats giant squid.

Sponge Information Page Read about these primitive animals.

Sponge Coloring/Information Printout A printable coloring/information page about sponges.

Sponge External Anatomy: Label Me! Printout Label the external anatomy of a sponge and the flow of water through it. Answers

Sponge Internal Anatomy: Label Me! Printout Label the cross-section of a sponge and the flow of water through it. Answers

Squid The squid is a fast-swimming invertebrate with ten arms.

Starfish Sea stars, another name for starfish, are animals that live on the ocean floor.

Zooplankton Zooplankton are tiny animals that float in the seas and other bodies of water.

An Enchanted Learning Web Page Biomes - Habitats

Arctic	Desert	Chaparral or Scrub		Taiga = Coniferous Forests	Grassland		Tropical Rainforest	Pond	Ocean
Antarctic	Tundra	Cave	City	Temperate Deciduous Forest	Savanna	Prairie	Freshwater Marsh	Swamp	Intertidal Zone	Coral Reef	Sunlit (Euphotic) Zone	Twilight (Disphotic) Zone

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