Deep sea
Because no sunlight reaches the deep sea, this production of light by living organisms is the primary light source in the abyss.
bioluminescence
Large underwater forests are formed by giant kelp, which is actually a type of this fast-growing organism, not a true plant.
algae (or brown algae / seaweed
This giant body of saltwater covers over 70% of Earth's surface.
the ocean
Instead of bones, a shark's skeleton is made completely out of this flexible material.
cartilage
Whales breathe air through these openings located on the top of their heads.
Blowholes
These sea creatures have five arms and can regrow a lost limb if it gets damaged.
sea star (or starfish)
Deep-sea anglerfish use a glowing lure called an esca attached to their heads to attract this.
Prey (food)
Sea otters are vital to kelp forest health because they eat these spiny invertebrates that otherwise overgraze on kelp.
sea urchins
High and low tides are mainly caused by the gravitational pull of this celestial body.
the Moon
Fish use these organs on the sides of their bodies to extract oxygen from the water.
Gills
This marine mammal holds the title for being the largest animal to ever live on Earth.
Blue whale
Tiny drifting organisms that form the foundation of the marine food web go by this collective name.
plankton
Hydrothermal vents spew superheated, mineral-rich water from beneath the ocean floor, powered by this underwater geological activity.
volcanic (or geothermal) activity
Coastal ecosystems where freshwater rivers meet and mix with saltwater from the ocean are called these.
estuaries
Sunlight only reaches down to about 600 feet in the ocean; below this point lies this dark ocean region.
twilight zone (or deep sea / aphotic zone)
Most bony fish use this internal gas bag to adjust their buoyancy without swimming continuously.
swim bladder
Dolphins and bats both use this high-pitched sound technique to "see" using sound waves.
echolocation
Jellyfish, sea anemones, and corals all belong to this phylum, named for their stinging cells.
Cnidaria
Unlike surface ecosystems driven by photosynthesis, deep-sea vent communities rely on bacteria that generate energy using this process.
chemosynthesis
Sea otters are considered this type of species because their presence has a dramatically large effect on maintaining the entire ecosystem structure.
keystone species
This ocean process occurs when deep, cold, nutrient-rich water rises toward the surface, feeding marine life.
upwelling
Sharks use specialized electroreceptive organs called the Ampullae of Lorenzini to detect this type of signal from prey.
electrical fields (or electric currents)
Seals, sea lions, and walruses all belong to this semi-aquatic marine mammal group.
pinnipeds
Instead of blood, sea stars and sea urchins pump seawater through this specialized system to move their tube feet.
water vascular system
Giant tube worms living near hydrothermal vents lack a mouth or gut; instead, they rely on symbiotic bacteria that process this smelly chemical compound (H_2S).
hydrogen sulfide
Instead of roots, giant kelp attaches to rocky ocean floors using these anchor-like structures.
holdfasts
Coral reefs have a symbiotic relationship with these photosynthetic microalgae that live inside their tissues.
zooxanthellae
Salmon are described as anadromous because they migrate from saltwater to freshwater for this purpose.
spawning (or reproducing)
Instead of teeth, blue whales and humpback whales use these fringed plates made of keratin to trap small prey.
Baleen
Octopuses and cuttlefish change color instantly using these specialized light-reflecting cells in their skin.
chromatophores