Creature for the Deep

Picture a cold, dark, motionless space where unbelievable pressure is exerted on you from all sides. No, you are not buried alive in some weird Stephen King novel; you are experiencing the world of deep water sea creatures. For deep water fish every day is Halloween, surviving in a dark, cold, hostile environment. The murky depths of the ocean is “aphotic,” meaning that little or no sunlight penetrates the water column so it is perpetually dark. At these depths, the water column is littered with debris such as dead animals, plankton, silt, and fecal matter — collectively known as “marine snow.”

The deep ocean is well below the thermocline, with water temperatures in the frigid range of 28 to 37 degrees Fahrenheit, unless a hydrothermal vent lies nearby to warm the water sometimes above the boiling point. These warm-water zones attract a lot of sea creatures that feed on plankton or other fish.

Nearly one atmosphere of pressure is exerted on a body every 33 feet of the water table, so at these depths enormous amounts of pressure are exerted on the shadowy life forms that tolerate these depths. Normally sunlight can penetrate the first 200 meters of water, so the aphotic zone begins at about a depth of 200 meters, extending down to almost 1,000 meters. It is estimated that 75 percent of the ocean is in the aphotic zone. Conversely, about 98 percent of sea life lives in the photic zone where there is abundant sunlight — about 25 percent of the surface area of the ocean. This means that about 2 percent of sea life occupies the other 75 percent of the ocean. The creatures in these shadowy depths are few and far between.

Many of these deep water creatures have grotesque appearances and equally scary names including wolf fish, coffin fish, ghost fish, hatchet fish, vampire squid, and fang-tooth fish. Deep water creatures have various adaptations to survive at these depths. Often, finding a meal or a mate is a tricky proposition. Many deep water fish have large eyes that are adapted to seeing in little or no light, or they are completely blind and rely more on smell or use of lateral lines to pick up vibrations in water. Some of these creatures create their own light source with bioluminescence, the ability to create a light source much like the firefly. Many deep water fish have very long, feeler-like organs that they dangle out like a large bloodworm to attract prey. These projections may also have some value for navigation similar to sonar. Deep water fish normally do not have a swim bladder or other excessive cavity space that can collapse under pressure, nor do they have much of a skeletal system. Instead, they have pliable, jelly like skin with few or no scales, adaptations for life under severe pressure. In fact, their skin is often transparent, helping them avoid predators and also an asset in navigation; black or red is also very common since these colors offer camouflage in the dark.

The fact that food can be scarce means that deep water fish need to be opportunists catching and eating prey when the opportunity presents itself. While most deep water fish are much smaller than their shallow water cousins, they usually have large teeth, large mouths, big bellies and strong digestive juices. This enables them to eat fish that are nearly their own size. The deep water creatures have very slow metabolism, and rely on ambush rather than chasing down prey to conserve energy. Some creatures merely process the waste products that sink down from the upper layers for energy.

Nature Note for 11/6/2016