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Exploring the saltwater environments that cover most of our planet.
Did you know that humans have explored more of the Moon's surface than the bottom of our own oceans? What secrets are hidden in the deep, dark blue?
The ocean is divided into layers called zones based on how much sunlight they receive. The top layer is the Sunlight Zone (Epipelagic), which goes from the surface down to meters. This is where most ocean life lives because plants need sunlight to grow. Below that is the Twilight Zone (Mesopelagic), reaching down to meters. It is very dim here, and no plants can grow. Finally, the Midnight Zone (Bathypelagic) is completely dark, cold, and under intense pressure. Creatures here often make their own light!
Imagine a scuba diver swims down to a depth of meters. 1. Check the range for the Sunlight Zone: to meters. 2. Since , the diver is still in the Sunlight Zone. 3. At this depth, the diver can still see colorful fish and maybe some seaweed!
Quick Check
In which ocean zone would you find the most plants and why?
Answer
The Sunlight Zone, because plants need sunlight to perform photosynthesis and grow.
Coral reefs are amazing structures built by tiny animals called polyps. Even though reefs cover less than of the ocean floor, they are home to over of all marine species! This incredible variety of life is why we call them the 'rainforests of the sea.' They provide food, shelter, and protection for thousands of creatures. Reefs also protect our coastlines from big waves and storms by acting as a natural barrier.
If a small coral reef has different species of fish and a local lake has only species: 1. Use a fraction to compare them: . 2. Simplify the math: . 3. The reef is times more diverse than the lake! This shows why reefs are so important for the planet's health.
Quick Check
Why are coral reefs so important if they only cover a tiny part of the ocean?
Answer
Because they support a huge amount of biodiversity, housing about one-quarter of all marine life.
Fish have to manage the salt in their environment. Saltwater fish live in water with a salinity of about . Because the ocean is saltier than their insides, the salt 'pulls' water out of their bodies through a process called osmosis. To stay hydrated, saltwater fish must drink a lot of seawater and use special cells in their gills to pump the extra salt back out. In contrast, freshwater fish never drink water because their environment is less salty than their bodies; they actually have to pee constantly to get rid of extra water!
What would happen if a saltwater fish was suddenly placed in a freshwater lake? 1. The fish's body is used to pumping out salt and drinking water. 2. In freshwater, there is no salt to 'pull' water out of the fish. 3. Instead, water would rush into the fish's cells. 4. The fish's cells would swell up like a balloon, which could be fatal. This is why most fish can only live in one type of water!
Which zone is completely dark and has no plant life?
What percentage of marine species live in coral reefs?
Saltwater fish drink large amounts of water to stay hydrated.
Review Tomorrow
Tomorrow, try to explain to a friend why a saltwater fish would have a hard time living in a garden pond.
Practice Activity
Draw a diagram of the three ocean zones and label one animal that might live in each layer.