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Understanding Ocean Zones: The Twilight Zone

Also known as the Mesopelagic zone, this life zone is the midwater range and is noted for very low levels of sunlight and virtual darkness for human eyes. This layer ranges from 200 meters to about 800 meters down. The plankton, which occupies the sunlight layer in profusion and provides a food source for most of the creatures living in that layer, either directly or indirectly, does not live in the twilight zone. Plankton needs adequate sunlight to thrive. The type of foods available to creatures living at these depth tend to be energy-poor and usually are characterized by detritus and bacteria, the things that drift down from the sunny creatures teeming and thriving at the surface. Most of the sea creatures living in this layer have low-energy tissues and sluggish lifestyles to cope with low food energy, since no algae can grow. Life here is noticeably sparse, the deeper you go.

Diving Video
Diving in the
Twilight Zone

JIM diving suitThe hydrostatic pressure in the twilight zone is much greater and special suits and diving crafts are necessary for humans to explore this layer of the water column. A highly specialized diving suit was designed and built for manned diving operations and exploration of these depths. Called the JIM suit, it is a type of atmospheric diving suit that creates artificial atmospheric conditions inside the suit (of 1 atmosphere, the same at sea level) regardless of the hydrostatic pressure outside the suit. It also protects the diver inside from the extreme cold temperatures at these depths and the risk of hypothermia. To date, the deepest dive for a JIM suit

Imagine yourself inside a JIM suit – it feels like a personal sized mini-sub. As you look out into the deep, deep blue water you see that life down here is pretty sparse. Soon, you see unfolding before your eyes what looks like a light show. One of the most spectacular and awe-inspiring phenomenon that a human diver visiting this realm can experience is bioluminescence. Many organisms’ body tissues are capable of emitting their own light – they glow in the dark. The colors range from blues to greens and even red, as some fish even emit red light as a form of infrared vision to help them see their prey in darkness. Although it isn’t completely dark in the twilight zone, many of the creatures that live in this ocean zone have developed this highly specialized adaptation for different reasons. A great many organisms throughout the water column (including those that live at the ocean surface) are capable of bioluminescence, but it plays a more critical role in the lives of creatures that exist in almost complete darkness. For example, some creatures, such as squid and octopi, emit clouds of glowing ink to evade predators. Others, such as jellyfish and some bony fish, use light to attract prey. In a world where sunlight casts just a faint blue glow for brief periods, organisms have adapted by generating their own light. The next ocean zone is in completedarkness all the time, the midnight zone...

six gill deep sea shark
Primitive deep sea six-gill shark

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