The Ocean Deep

Seventy percent of the Earth’s surface is under the ocean, and only a small portion is in shallow water along continental shelf areas.  The ocean is divided into five zones; the sunlight zone, above 650 feet; the twilight zone, extending to 3300 feet; the midnight zone, down to 13,000 feet; the abyssal zone, down to 21,300 feet; and the hadal zone, extending to the bottom of the ocean.  Below 3,000 feet, no light penetrates from the surface; the water temperatures are freezing; and oxygen levels are very low.  The pressure exerted on any surface at sea level is 14.7 pounds per square inch (psi), and humans can withstand three to four times this amount, or 45 psi to 60 psi.  At 3,000 feet deep, the pressure is 1,345 psi.

Pressure keeps sea water from becoming solid ice, even when it is at freezing temperatures.  It also makes exploring the ocean difficult, requiring special submersible vehicles.  Everything moves more slowly under pressure, and a submersible can take an explorer deep into the ocean given enough time and oxygen.  Deep sea creatures can survive because the structure of their bodies is lean and contain no air spaces.  Let’s take a look at a few of the wondrous creatures that live in these habitats.

In the darkness of deep areas, many species find food and mates by touch.  Others may use bioluminescent communication – the ability to create light from a chemical reaction between luciferin and oxygen within an organism’s body.  Lights show up as spots of various colors on different parts of the body and may be used for attracting a mate, confusing a predator, or attracting prey.  Lanternfish have several spots located on their heads, undersides, and tails.  Female anglerfish and dragonfish have a shaft that protrudes from their head out in front of their mouths with a glowing tip attracting prey within striking distance.  Gulper eel use the lighted tip of their tail as a lure to attract a meal.

Tripod fish have two pelvic fins and a tail fin that are elongated and can be filled with fluid to stiffen them, allowing the fish to stand on the ocean bottom while conserving energy.  Two long, wavy pectoral fins act as  arms to detect prey floating or swimming by and push the prey toward their mouths.  Fangtooth fish is another species that can detect vibration and nearby movement.  This species is only six inches in length, but have the largest teeth in proportion to their body size of any fish in the ocean.  The long lower fangs fit into pouches in the roof of their mouths so their teeth do not pierce their brain cavity.

The dragonfish, another small fish about six inches long, has a frightening array of teeth located on its jaws and tongue.  Their teeth are transparent and their bodies are black, making them impossible to see even in depths where there may be some light.  The jaws are loosely hinged, allowing the fish to open its mouth wider than normally hinged jaws would allow.  Prey swimming nearby may not notice the wide opening, nor be able to detect the transparent teeth, making the dragonfish a top predator of invertebrates, squid, and shrimp.  In addition, when biting, they inject a highly toxic poison to paralyze and kill their prey.  This toxin can be dangerous to humans getting bitten or attempting to eat this species.

^{Giant spider crab by Michael Coghlan, Jan 2014; Gulper eel by Claf Hong, Mar 2005; Lanternfish, Myctophum punctatum1 by Emma Kissling}

Some fish practice diel vertical migration, a pattern of movement where a species feeds near the surface at night and moves back into deeper waters to rest during the day.  Lanternfish come up to feed on zooplankton and fangtooth fish feed on squid in shallow waters.  Some species, including anglerfish and gulper eels, have elastic-like skin for their mouths and stomachs.  Mouths can be opened extremely wide to swallow prey larger then themselves.  The food is contained in a similarly elastic stomach which shrinks slowly as digestion progresses.  Several different species of spider crabs roam the ocean depths scavenging for meat or plant material that falls to the bottom.

Deep-sea animals are seldom seen, but are not immune from climate change and human impacts.  Scientists continue to study changes in deep-sea food webs caused by overfishing, ocean acidification, and expanding low-oxygen zones.  Learn more about the habitat and species of these areas at the Jurica-Suchy Nature Museum at Benedictine University or your local nature museum or aquarium.