Ocean as Habitat

Welcome to Earth's Oceans

Each line on this page represents 10 meters of ocean depth. As you scroll along, take notice of the staggering scale of Earth’s oceans and the diversity of marine life overall. This page will be divided into the five recognized layers of the ocean in descending order. It will start from the top surface of the ocean at 0m and go all the way down to the lowest known point of Earth’s oceans – the Mariana Trench, almost 11,000m below the surface off the coast of Japan.

With this, take note of the range and diversity of marine life both between each layer and within each layer themselves. (Note: all images and their accessible description alt texts can be found through the 'browse' tab in the menu at the top right)

0-200m

The upper 200 meters of the ocean is called the Euphotic, or "Sunlight," Zone. The euphotic zone is the only layer that receives enough light for photosynthesis to occur. Only a small amount of light penetrates beyond this depth. The Sunlight Zone is home to a wide variety of marine species because plants can grow there and water temperatures are relatively warm. Human fishing and pollution heavily affects this layer which has a great impact on wider ecosystems. For example, the seabird commonly known as the albatross eats fish from the euphotic zone. Fish in the euphotic zone have a high concentration of microplastics in their bodies from human pollution and the albatross die from an over accumulation of plastics in their bodies. Turtles often choke on the plastic bags they believe are jellyfish. The Pacific Ocean Garbage Patch is devastating proof of the human impact on the ocean. The Pacific Ocean Garbage Patch is a mass accumulation of human made plastics on the surface on the Pacific Ocean. The Microplastics and other contaminants of fish and animals in the sunlight zone seep into other zones of the ocean by being eaten or falling down into other zones to be eaten or decompose. Even though it's the smallest zone, it has a huge impact.

On left NOAA Pacific Island Garbage Patch Map and on right Albatross

200 - 1000m

The Mesopelagic Zone, better zone as the Twilight Zone, is compromised mostly of small fishes and invertebrates (Over 90%). Among these small fishes are filter feeders (species that feed by filtering the food particles and waste in the water from other species), grazers (species that rely on plant matter and algae), and predators (species that feed on other animals in the same zone or the epipelagic zone). Ex) Angel Shark, Coelacanth, Clam, Copepod, Crab, Cuttlefish, Eels, Echinoderms, Fiddler Crab, Gastropods, Gray Whale, Greenland Shark, Hatchetfish, Hermit Crab, Horseshoe Crab, etc.

Many mesopelagic species migrate to near the surface (epipelagic zone) to feed on plankton in the evening and night Mesopelagic species produce “marine snow” (waste), which is a major food source for species inhabiting the ocean floor, like sponges and corals.

Some fishing industries are now developing ways to harvest tons of small mesopelagic creatures, which could disrupt the food chain. Overfishing of species from the epipelagic zone can indirectly contribute to food scarcity for those in the mesopelagic zone

Fish have ingested more microplastics in the upper mesopelagic layer. This is a threat to biodiversity and ecosystems.

1000 - 4000m

The Bathypelagic or Midnight Zone is the third layer of the ocean. At this depth no light reaches whatsoever and any organisms living there are in complete darkness. Surprisingly, the Midnight Zone is the largest layer of the ocean and makes up 70% of all seawater. It is often recognized as Earth's largest habitat. Ironically, this zone and the zones below it are some of the least explored out of any habitat on Earth. Due to the layer's complete darkness and sheer size, scientists face many challenges trying to document marine life and their characteristics within the Midnight Zone. A careful balance has to be stricken between illuminating the water such that scientists can meaningfully study the habitat and keeping the lighting subtle enough as to not scare off the natural fauna. As a result, the darkness of the Midnight Zone works as a disadvantage to people researching it.

But while the darkness of the Midnight Zone serves strictly as a disadvantage to humans, that same darkness is both a disadvantage and an advantage to the marine life that end up there. Most often, it serves as a disadvantage to the organisms that are not supposed to be there. Recall that marine life is certainly not held to the strict range of depths that they are associated with. Many marine organisms from the Twilight Zone end up lost and veer into the Midnight Zone. These creatures, not acclimated to the darkness, either end up permanently lost or must find their way back to the Twilight Zone where they can see enough to function normally. The creature tries to find which way is up by searching for light. Just as they seem they won’t make it back, they catch a flash of light.

Unfortunately for many of these lost creatures, opportunistic organisms use something called bioluminescence to lure in unsuspecting prey. Thinking that the light of a bioluminescent organism is the light of the sun above them, they swim towards it in an effort to get back to its home habitat. At this point, the easily eats its prey once they unknowingly swim right to them. Pictured above is a the anglerfish, a fish widely known to use a bioluminescent bait that hangs above their mouth to catch lost or confused sea creatures.

Accordingly, just as the darkness of the Midnight Zone may spell disaster for certain organisms, it may provide an opportunity for others (like the anglerfish). The Midnight Zone’s fauna evolved to embrace the complete darkness that it lives in, lighting its own way through the ocean, seeing in its own way, or forgoing its sense of sight completely

You may have heard the joke, “What do you call a fish with no eyes… a fsh”, but for the grideye fish, this joke also works in its literal sense. The grideye fish doesn’t “see” in the same way humans do. In fact, because it lives in total darkness 3000 meters deep at the ocean floor, it doesn’t even have eyes. Instead, the grideye fish has photovoltaic cells. Scientists believe these photovoltaic cells simply sense the presence of brightness or darkness, alerting the fish of any changes in trace amounts of light. The grideye uses this information to find potential prey swimming above it, whether that be small organisms disrupting the normally undetectable amount of light they displace or the bioluminescence that the prey organism usually uses to its advantage.

In line with the layers being interconnected in various ways, organisms "from" the Twilight Zone may teter between the Twilight Zone and the Midnight Zone changing its depth and layer that it resides in from month to month or even day to day. For example, zooplankton from the Twilight Zone often sink down to the Midnight Zone at night, using the darkness of the layer as a shield from predators. Additionally, organisms with vulnerable larvae stages can deliberately go down to reproduce in the Midnight Zone to protect its offspring from predators. From there, the larvae stay in the Midnight Zone until they mature and grow. Once the larvae is strong enough to survive in the semi-illuminated Twilight Zone, they float back up and live the rest of their lives.

But just as creatures may venture from the Twilight Zone to the Midnight Zone, marine creatures dwelling at lower depths of the Midnight Zone may just as easily find themselves in the next layer of the ocean...

It's still going...

Wow that was a lot of scrolling

4000 - 6000m

The fourth layer of the ocean is the Abyssopelagic or Abyssal Zone. Now that we are far from any trace amount of sunlight, you might be wondering where the energy of the ecosystem comes from. After all, producers generally are the starting point for all energy in a food chain and they traditionally get energy from the sun. Still, indirect energy from the sun may trickle down in the form of dead sea creatures from the upper layers.

Pictured above is a phenomenon known as whale fall in which a whale dies and its carcass sinks into the floor of the Abyssal Zone. Interestingly, in a certain sense, the end of the whale’s life can mark the beginning of many more creatures’ respective lives. Miniature ecosystems are sustained scavengers feeding on this carcass and opportunistic predators looking to pick off those scavengers for their next meal. Still, it would be highly impractical for the entire layer’s producers to be sustained by the sheer chance of large marine life sinking to the ocean floor. Therefore, other producers have found a way to thrive in the Abyssal Zone.

Above is a hydrothermal vent. The vent constantly emits black smoke as a result of chemical reactions and heat contained in the earth’s crust along the seafloor. Incredibly, ocean life has evolved to be able to utilize the emissions of vents like this through a process known as chemosynthesis. Chemotrophs take in the seemingly useless smoke and chemicals and convert it into energy, acting as producers of the Abyssal Zone.

Pictured is the small, but mighty Sulfolobus. This chemotroph takes in sulfur from hydrothermal vents. From there, the producer serves as the bottom of the food chain for all other creatures in the Abyssal Zone.

This enables the survival of strange deep sea creatures like the dumbo octopus. Unable to rely on its sense of sight, this octopus uses its oddly shaped fins on the top of its head (which look like ears, leading to its aptly given name) to search the sea floor for potential prey. It uses its short, blunt tentacles to scour the ocean floor in hopes of finding food without light to help it see.

6000 - 11000m

The Hadalpelagic Zone is the deepest part of the ocean where pressures reach over 1,000 standard atmospheres, thus forcing its organisms to become highly specialized. Hadal organisms are highly adaptive to any available nutrients such as any particulate organic matter carried by currents, the carcasses of fish, gelatinous organisms, dead whales, and even wood debris from sunken ships. By ingesting hard to digest waste products, hadal zone organisms recycle waste products and energy from decaying organisms back into the environment to allow other trophic layers to benefit. The most important contribution from the Hadal Zone is its ability to act as a black carbon sink. Globally, scientists estimate that black carbon is stored in the Hadal Zone at a rate of 1.0 ± 0.5 Tg per year which reduces the amount of carbon in the atmosphere which reduces the effects of global warming, thus benefiting all aquatic and even land organisms.

Image of Giant Amphipod

Found in the deepest part of the ocean giant amphipods can reach a size of 141 millimeters with a weight of 45 grams. Amphipods serve the environmental role of decomposers as they recycle dead matter back into the environment to allow other trophic levels to benefit.

New Deep-Sea Pictures: Snailfish, Eels Found in Trench

Snailfish are the most dominant family of fish found in the Hadal Zone These gelatinous fish are translucent, so much so that you can see all of their inner organs.

To Adapt to the extreme pressure of the hadal zone without a shell, snailfish do not contain any air spaces. Instead, hadal snailfish possess gelatinous goo underneath their skin to combat the extreme pressures. As a fish with fins, snailfish possess the capabilities to consume amphipods, decapods, and polychaetas. As a result snailfish act as a selective pressure to regulate the populations of amphipods, decapods, and polychaetas to prevent the disruption of the ecosystem.

Striped Cusk-eels adapted to hunting prey in the absence of light by evolving to possess pelvic fins on their chin. By possessing pelvic fins on their chin, cusk-eels can use the sense of feel more to locate invertebrates, crustaceans, and other small bottom-dwelling fishes. As a result the cusk eel acts as a selective pressure to invertebrates, crustaceans, and fishes to prevent the disruption of the ecosystem.

It gets deeper than this...

A bioluminescent jellyfish is shown in an image taken during exploration of the Marianas Trench Marine National Monument area in the Pacific Ocean near Guam and Saipan,

You have officially reached the bottom of the ocean - the Mariana Trench 11,000 meters deep

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