The Open Ocean
The open ocean, or pelagic zone, consists of everything in the ocean outside of coastal areas. The demersal zone is everything in the ocean near the sea floor or the coast. Separated into epipelagic, mesopelagic, bathypelagic, abyssopelagic and hadopelagic subzones, areas in the pelagic zone are distinguished by their depth and the ecology of the zone. The epipelagic zone is closest to the surface and stretches down 200 m. An abundance of light allows for photosynthesis by plants and nutrients for animals like tuna and sharks. The mesopelagic zone, also known as the twilight zone, begins at 200 m down and reaches a depth of 1,000 m and has a little light but not enough for photosynthesis to occur. The bathypelagic zone follows from 1000-4,000 m in depth, a subzone containing the infrequent bioluminescent organism. Unique animals like the marine hatchet fish and giant squid live in this subzone, surviving mostly on the detritus that drifts down from the epipelagic zone. The abyssopelagic zone is located from 4,000 m to directly above the ocean floor and is a completely dark area home to colorless and blind animals. The deepest subzone is the hadopelagic zone, a name that originates from the Greek underworld Hades and refers to the ocean water in submarine trenches.
Scientists generally classify the epipelagic and mesopelagic zones into what is known as the photic zone - or where light penetrates the water. Anything below the photic zone is referred to as the aphotic zone.
Animals of The Epipelagic Zone
The zone best known to humans is where people can easily go scuba diving and many marine mammals are found. This area is packed with ocean life because of the sunlight that penetrates the surface. Much of the life in the aphotic zone depends on detritus floating down from the epipelagic zone.
Animals of The Mesopelagic Zone
Known as the twilight zone, the mesopelagic zone meets the photic zone above and becomes very dark as depth increases. Animals that produce bioluminescence, or light, inhabit this subzone. Because nutrients are limited here, some animals rise to the photic zone at night for food. Many animals in this subzone can eat animals larger than themselves because they are equipped with large sharp teeth with expandable jaws and stomachs. Animals in the mesopelagic zone include the bigscale fish which lives in the depths between 150-1,000 m, an animal with oversized scales and bony plated head. Similar to other fish in this zone, the bigscale relies on specially developed lures to catch its prey off guard and to save energy in a nutrient poor subzone. The ctenophore is a relative of the jellyfish and is also a bioluminescent organism and has adapted its iridescent cilia, used for locomotion, to scare away its predators. Ctenophores come in many forms and typically capture crustaceans and fish with long tentacles. A more complicated bioluminescent organism is the Firefly squid, an animal with one photophore on its head, another around the eyes, one on the body surface and the remaining one on the tips of its tentacles. Possible uses for the photophores are predator deterrence, communication, lures for prey and a flashlight to see in the dark when hunting.
The hatchetfish looks frightening but it is only a few inches long with a huge jaw and long teeth. With photophores underneath their body and under their eyes, it is thought that this fish may also be hiding its silhouette so that it's invisible to predators swimming below. Dragonfish and viperfish are very similar in that they both have an enormous mouth, sharp pointy teeth, big eyes, and large stomachs. They are thought to swim up at night to hunt. Both species have been found hunting in the deep sea and in surface waters with their bioluminescent lures.
Adult snipe eels look like a long piece of silly putty stretched out with a flat little head at one end. The jaws of the snipe eel curve out to trap shrimp antennae in the teeth. Also present in the mesopelagic zone are siphonophores, animals related to the jellyfish that stun their prey with a special tentacle. Siphonophores can also form a gas-filled float.
Animals of the Bathypelagic Zone
Animals living in the bathypelagic zone rely on detritus for food or on eating other animals in this zone. At this depth and pressure, the animals most commonly found are fish, mollusks, crustaceans, and jellyfish. Sperm whales will hunt at these depths on occasion to prey on giant squid. Black and red are the predominant colors of animals here and any bioluminescence is usually blue since red is not visible at these depths. The most common mollusk in the bathypelagic zone is the vampire squid, an animal that can turn itself inside-out to use its spiky tentacles to deter predators or capture prey.
The tentacles are often thrown over prey like a net from above. The snake dragonfish resembles the viperfish or dragonfish of the mesopelagic zone and also comes up to hunt at night but has to travel further as it lives in deeper water than the others. The anglerfish of the bathypelagic zone is well known for its enormous mouth and a lure that resembles a flashlight on its head. Not only does the angler fish have huge long teeth on the jaws, it is also equipped with teeth in its throat! Males of this species are found in the form of a tiny parasitic fish carried by the female near her genitals. Both sexes can be found anywhere from the surface to the deepest waters.
Amphipods are crustaceans and scavengers in the bathypelagic zone that hide using a transparent red body. Other crustaceans found in the bathypelagic zone include shrimp. Echinoderms seem to do well in deep ocean water, although they are not usually found in the open ocean. They survive by scouting out detritus on the ocean floor or by swimming through the water hunting for floating food. Slime stars are in the echinoderm family and can reach up to 21 cm in length—large for an echinoderm.
Animals of the Abyssopelagic Zone
There are only a few organisms adapted to survive in the abyssopelagic zone, a subzone located from 4,000 m to the bottom with freezing temperatures and incredible pressures. Deeper than the abyssopelagic zone are the canyons and submarine trenches of the hadopelagic zone. Animals capable of living at these depths include some species of squid, such as the deep-water squid, and octopus. As an adaptation to the aphotic environment, the deep-sea squid is transparent and also uses photophores to lure prey and deter predators. Other animals of the abyssopelagic zone include basket stars, seapigs, and seaspiders. Basket stars are echinoderms with an arm span larger than 25 cm living on the ocean floor or on another animal, feeding on detritus floating down from above. Like many echinoderms, the loss of a limb is not a big deal since they will grow back. The seapig is another echinoderm that looks like an ugly sea cucumber and can eat mud like an earthworm. Some echinoderms, like the swimming cucumber, use wing-like structures to swim as if they were flying through the water. The sea spider is a crustacean and actually resembles a spider walking on the ocean floor. The sea spider has a hose-shaped mouth and eats anemones and echinoderms. Its leg span reaches 30 cm or larger. Other crustaceans living at these depths have adapted by becoming transparent and have evolved without eyes because they serve no purpose at these depths.
Share your thoughts
Feedback & Citation
Oceanography News :: ScienceDailyUnparalleled views of Earth's coastal zone with HREP-HICO
Scanning the globe from the vantage point of the International Space Station is about more than the fantastic view. While cruising in low Earth orbit, the space station HICO and RAIDS Experiment Payload-Hyperspectral Imager for the Coastal Ocean, or HREP-HICO, gives researchers a valuable new way to view the coastal zone.
Sulfur finding may hold key to Gaia theory of Earth as living organism
Is Earth really a sort of giant living organism as the Gaia hypothesis predicts? A new discovery may provide a key to answering this question. This key of sulfur could allow scientists to unlock heretofore hidden interactions between ocean organisms, atmosphere, and land -- interactions that might provide evidence supporting this famous theory.
Hidden lives of elephant seals: Record-setting dive more than a mile deep
The same researchers who pioneered the use of satellite tags to monitor the migrations of elephant seals have compiled one of the largest datasets available for any marine mammal species, revealing their movements and diving behavior at sea in unprecedented detail.
Arctic seabirds adapt to climate change
The planet is warming up, especially at the poles. How do organisms react to this rise in temperatures? Biologists have now shown that little auks, the most common seabirds in the Arctic, are adapting their fishing behavior to warming surface waters in the Greenland Sea. So far, their reproductive and survival rates have not been affected. However, further warming could threaten the species.
First satellite tag study for manta rays reveals habits and hidden journeys of ocean giants
Using the latest satellite tracking technology, conservationists have completed a ground-breaking study on a mysterious ocean giant: The manta ray.
Push from Mississippi kept Deepwater Horizon oil slick off shore
Geoscientists offer an explanation for why the Deepwater Horizon oil spill didn't have the environmental impact that many had feared. Using publicly available datasets, their study reveals that the force of the Mississippi River emptying into the Gulf of Mexico created mounds of freshwater which pushed the oil slick off shore.
Potential instability in West Antarctic Ice Sheet from newly discovered basin size of New Jersey
Scientists have uncovered a previously unknown sub-glacial basin nearly the size of New Jersey beneath the West Antarctic Ice Sheet near the Weddell Sea. The location, shape and texture of the mile-deep basin suggest that this region of the ice sheet is at a much greater risk of collapse than previously thought.
New weak point discovered in the Antarctic ice sheet
The Filchner-Ronne Ice Shelf fringing the Weddell Sea, Antarctica, may start to melt rapidly in this century and no longer act as a barrier for ice streams draining the Antarctic Ice Sheet, new research shows.
Antarctic octopus study shows West Antarctic Ice Sheet may have collapsed 200,000 years ago
Scientists have found that genetic information on the Antarctic octopus supports studies indicating that the West Antarctic Ice Sheet could have collapsed during its history, possibly as recently as 200,000 years ago.
Plastic trash altering ocean habitats
A 100-fold upsurge in human-produced plastic garbage in the ocean is altering habitats in the marine environment, according to a new study.
Effect of groundwater use: Using water from wells leads to sea level rise, cancels out effect of dams
As people pump groundwater for irrigation, drinking water, and industrial uses, the water doesn't just seep back into the ground -- it also evaporates into the atmosphere, or runs off into rivers and canals, eventually emptying into the world's oceans. This water adds up, and a new study calculates that by 2050, groundwater pumping will cause a global sea level rise of about 0.8 millimeters per year.
70 percent of beaches eroding on Hawaiian islands Kauai, Oahu, and Maui
An assessment of coastal change over the past century has found 70 percent of beaches on the islands of Kaua»i, O»ahu, and Maui are undergoing long-term erosion, according to new results.
Stalagmite research suggests Earth has two modes of responding to change
By analyzing stalagmites, a team of researchers has determined that the climate signature in the tropics through four glacial cycles looks different in some ways and similar in others when compared to the climate signature at high latitudes. The results suggest that Earth's climate system might have two modes of responding to significant changes.
Increasing speed of Greenland glaciers gives new insight for rising sea level
Changes in the speed that ice travels in more than 200 outlet glaciers indicates that Greenland's contribution to rising sea level in the 21st century might be significantly less than the upper limits some scientists thought possible, a new study shows.
Marine food chain becomes clearer with new revelations about prey distribution
A new study has found that each step of the marine food chain is clearly controlled by the trophic level below it -- and the driving factor influencing that relationship is not the abundance of prey, but how that prey is distributed.
Arctic sea-ice loss didn't happen by chance
The ongoing rapid retreat of Arctic sea ice is often interpreted as the canary in the mine for anthropogenic climate change. In a new study, scientists have now systematically examined the validity of this claim. They find that neither natural fluctuations nor self-acceleration can explain the observed Arctic sea-ice retreat. Instead, the recent evolution of Arctic sea ice shows a strong, physically plausible correlation with the increasing greenhouse gas concentration. For Antarctic sea ice, no such link is found – for a good reason.
Ireland's Aran Islands: Old maps and dead clams help solve coastal boulder mystery
Perched atop the sheer coastal cliffs of Ireland's Aran Islands, ridges of giant boulders have puzzled geologists for years. What forces could have torn these rocks from the cliff edges high above sea level and deposited them far inland? While some researchers contend that only a tsunami could push these stones, new research finds that plain old ocean waves, with the help of some strong storms, did the job.
Global warming refuge discovered near at-risk Pacific island nation of Kiribati
Scientists predict ocean temperatures will rise in the equatorial Pacific by the end of the century, wreaking havoc on coral reef ecosystems. But a new study shows that climate change could cause ocean currents to operate in a way that mitigates warming near a handful of islands right on the equator.
Pacific islands on equator may become refuge for corals in a warming climate due to changes in ocean currents
Scientists have predicted that ocean temperatures will rise in the equatorial Pacific by the end of the century, wreaking havoc on coral reef ecosystems. But a new study shows that climate change could cause ocean currents to operate in a surprising way and mitigate the warming near a handful of islands right on the equator. As a result these Pacific islands may become isolated refuges for corals and fish.
Scientists provide first large-scale estimate of reef shark losses in the Pacific Ocean
First study to provide estimates of reef shark losses in the Pacific Ocean are sobering. Researchers noted the enormous detrimental effect that humans have on reef sharks.
Help us continue to share the wonders of the ocean with the world, raise awareness of marine conservation issues and their solutions, and support marine conservation scientists and students involved in the marine life sciences. Join the MarineBio Conservation Society or make a donation today. We would like to sincerely thank all of our members, donors, and sponsors, we simply could not have achieved what we have without you and we look forward to doing even more.
