As any marine biology student knows, the ocean is not one homogenous block of water. Covering over 70% of the Earth’s surface, the ocean spans from the balmy equator to the frigid poles. The ocean is also very deep with temperatures getting colder and water pressure increasing at greater depths. These changes mark different layers in the sea and at different layers animals require certain adaptations to survive.
The Sunlight Zone is the Top Ocean Layer
NOAA describes the various layers of the ocean in its National Weather Service article “Layers of the Ocean”. The sea surface down to 200 meters (660 feet) is known as the Epipelagic Zone or the Sunlight Zone. This zone varies greatly from the tropics to the poles. Tropical coral reefs are one of the most biodiverse ecosystems on the planet, home to schools of tropical fish, shrimps, seastars, and more. However, the Epipelagic Zone is also home to temperate kelp forests and swimming penguins of Antarctica.
The Twilight Zone is in the Ocean
After the Sunlight Zone marine biology students learn about the Mesopelagic Zone, or the Twilight Zone, which occurs from 200 meters to 1000 meters. NOAA writes that sunlight in this ocean layer is faint and temperature fluctuates greatly. The Twilight Zone is home to the thermocline, an area where temperature changes quickly with depth. Paddy Ryan writes about many of this layer’s creatures in Te Ara’s “Deep Sea Creatures – The Mesopelagic Zone”. Ryan notes that most of the food in this layer comes from the Epipelagic Zone and that fish will travel upwards at night to eat it. These include lanternfish (Myctophids) and bristlemouths (Gonostomatids). Also found in this layer are the blobfish (Psychrolutes species) and the prickly shark (Oxynotus bruniensis). Krill, comb jellies, squid, and many other animals can also be found here.
Marine Creatures in the Midnight Zone
NOAA writes that the Bathypelagic Zone is also called the Midnight Zone as sunlight never reaches its depths of 1,000-4,000 meters (3,300-13,100 feet). The only light found is from bioluminescent animals. Temperatures are usually a constant 4 °C (39 °F) and at the deepest edge of the Midnight Zone pressure is at 5850 pounds per square inch. Sperm whales will dive to these depths to find food. The Midnight Zone is also home to many animals including angler fish, eels with giant jaws, and tube worms of hydrothermal vents. Marine biologists have found deep sea corals at depths of 2,000 m.
Finding Marine Life in the Abyss
The Abyssopelagic Zone, or simply the Abyss, occurs from 4,000 meters down to 6,000 meters (13,100 feet to 19,700 feet). Even at these crushing depths and frigid temperatures marine biologists have found fish. As Rebecca Morelle writes for the October 7, 2008 BBC article “‘Deepest ever’ living fish filmed” a school of 30 cm (12 in) Pseudoliparis amblystomopsis was found off of Japan at a depth of 7.7 km (4.8 mi). The fish is also sometimes called a liparid.
The Deepest Part of the Ocean
NOAA continues that the Hadalpelagic Zone is the deepest layer of the ocean, extending from 6,000 meters (19,700 feet) to a depth of 10,911 meters (35,797 feet) in the Mariana Trench off of Japan. At such depths the temperature is constantly just above freezing and the weight of water is greater than 8 tons per square inch. NOAA compares this to the weight of 48 Boeing 747 jets. Yet life lives here too reports NOAA; in 2005 a type of plankton called foraminifera was discovered in a trench southwest of Guam. This recent discovery just goes to show that marine biologists still have much to learn about the ocean and its inhabitants.
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