The ocean has long been a wondrous mystery for adventurers, scientists, and dreamers who seek to understand the vast expanse of its waters.
Covering 70% of the earth’s surface, the ocean offers near-endless wonders as we explore its various zones.
From the intertidal zone, where land meets the sea, to the depths of the oceanic zone, where darkness rules, each oceanic zone presents unique characteristics, inhabitants, and seabed structures.
Intertidal Zone: The Ever-Shifting Shoreline
At the point where the land meets the sea, we find a unique habitat that undergoes constant change due to the movement between high tide and low tide.
This dynamic zone extends along coastlines, embracing the area between the high tide mark and the low tide mark.
With the changing of tides, life in the intertidal zone has uniquely adapted to living in both aquatic and terrestrial environments.
Including both rocky shores and sandy beaches, the intertidal zone is a harsh environment,s but is diverse with life across its gradient.
Sea stars, snails, seaweed, algae, crabs, barnacles, mussels, and kelps are commonly found in this zone, often inhabiting shallow rockpools that have been left behind by a retreating tide.
The intertidal zone is separated into three smaller zones: the high tide, low tide, and middle tide areas, all of which bring with them their own unique life.
Neritic Zone: A Sunlit Biodiverse Wonder
Depth: 0-200 meters (0 – 656 feet)
Location: From the shore to the continental shelf
Encompasses zones: Epipelagic
From the water’s edge at the shoreline to the edge of the continental shelf, we find a lifebringing habitat known as the neritic zone.
The neritic zone, also referred to as the sublittoral zone, is the area of the ocean closest to the coastline and extends from 0 – 200 meters deep (this can differ, but generally corresponds with the continental shelf).
The neritic zone, or coastal ocean, is shallow and therefore allows sunlight to penetrate its depths all the way to the seafloor.
Because of the presence of light, photosynthesis is possible, which brings with it a steeming abundance of life hosted mostly by coral reefs.
While the neritic zone covers the shallow areas over the continental shelf, the epipelagic zone is defined based on the penetration of sunlight. They overlap because, in many regions, the continental shelf coincides with areas where there is enough sunlight for photosynthesis. The separation arises from the different criteria used to define them—one based on depth over the continental shelf (neritic), and the other based on the penetration of sunlight (epipelagic).
Epipelagic Zone: The Sunlight Zone
Also known as the sunlight zone, the epipelagic zone makes up the entire Neritic zone, and covers the areas from 0 – 200 meters deep (0 – 656 feet). It hosts approximately 25% of the ocean’s biodiversity. It is also known as the euphotic zone and is defined as the upper layer of the ocean where there is enough sunlight for photosynthesis to occur.
Because of the light penetration and heat from the sun, plant and animal life thrive in this zone.
Starting from the smallest phytoplankton to large predators such as sea turtles, sharks, and whales.
Not only does this zone support a permanent home for an abundance of sea creatures, but it also acts as a nursery for young oceanic species to mature and a safe place for mature adults to reproduce.
Life in the Epipelagic Zone
As mentioned above, the Epipelagic Zone holds around 70% of the ocean’s biodiversity. This is mainly due to the abundance of light that penetrates to zone depths.
With the availability of light, photosynthesizing microorganisms such as phytoplankton become abundant.
These microscopic organisms are the fundamental building blocks of ocean life.
Along with these plankton, come an array of larger flora such as seagrass, algae, mangroves, and kelp, not to mention the reef-building corals that provide nurseries and homes for juveniles and smaller species.
Apart from reef-inhabiting life, such as clownfish, anemones, crustations, and a variety of invertebrates, larger marine species, such as whales, can be found feeding on plankton along the stretches of this zone.
Furthermore, this zone is often used as a safe place for breeding and as a nursery for larger fish such as sharks and tuna.
The Epipelagic Zone is undoubtedly the most life-abundant zone in the ocean.
Oceanic Zone: A Descent Into the Dark Unknown
Depth: 200-10,935 meters (656-35,900 feet)
Location: From the continental shelf to the open ocean
Encompasses zones: Mesopelagic, Bathypelagic, Abyssiopelagic, Hadalpelagic
When the neritic zone meets the continental shelf, a steep include begins, and with it, the start of the oceanic zone, which extends out into the open ocean.
In some parts of the ocean, part of the epipelagic zone lies in the oceanic zone, but as we travel deeper, light begins to fade, and so does the life that is found with it.
The oceanic zone covers depths of 200 meters down to 10,935 meters (the deepest point in the ocean) and includes the mesopelagic zone, bathypelagic zone, abyssopelagic zone, and hadalpelagic zone, each of which differs in depth, light, temperature, and life.
Mesopelagic Zone: Enter the Twilight Zone
Spanning from 200 to 1,000 meters (656-3,280 feet) in depth, the mesopelagic zone can be characterized by its fading sunlight, moving from bright, full-spectrum light to a dull twilight.
Lanternfish, bristle-mouthed fish, and other deep water aquatic animals such as squid and jellyfish are found in this zone, with special adaptations to survive in low light conditions.
For example, specialized eyes and bioluminescence are used by some species to navigate and hunt.
The Mesopelagic zone contains the thermocline, which is the region where water rapidly decreases in temperature due to increasing pressure and a reduction of sunlight as depths increase.
The thermocline and changing light bring with them constant temperature changes.
This forms a transition layer between surface water and deeper water, which contributes to the zone’s alternative name – the middle zone.
Life in the Mesopelagic Zone
As we travel deeper into the ocean, life begins to become scarce. This is mostly due to the lack of sunlight, which reduces the possibility for photosynthesis, as well as drastically decreases the water temperature.
That said, this zone is not barren.
Some species of zooplankton can be found at these depths, which provides a food source for smaller fish, jellyfish, and shrimp, which are then fed on by larger animals such as eels or swordfish.
As there is no light in this zone, photosynthesis does not take place, and there is, therefore, no flora or reef-building coral.
Bathypelagic Zone: Welcome to the Midnight Zone
As we plunge even deeper into the ocean’s depths, we find the light fading out completely, leaving us in utter darkness.
The bathypelagic zone, spanning from 1,000-4,000 meters (3,280-13,123 feet), has no light penetration from the sun, which is why it’s also known as the midnight zone.
In this zone, the only light that exists is from the bioluminescence emitted from life that has managed to survive so deep.
The temperature of the bathypelagic zone, unlike the mesopelagic zone, is constant and never moves far from its near-freezing 39°F (4°C).
Pressure from the above water at these depths is immense and can reach over 5850 pounds per square inch.
That said, the ridiculously cold water and eye-popping pressure don’t stop creatures like sperm whales from diving into the zone’s depths in search of food.
Life in the Bathypelagic Zone
In the bathypelagic zone, you will find no flora, not even phytoplankton. As there is no light, organisms that require photosynthesis cannot survive.
That said, there is still life in these dark, freezing depths.
Sharks, squid, octopuses, and other carnivorous creatures are found in the bathypelagic zone, many of which rely on carcasses that fall from above zones.
Many animals at these depths have soft, translucent skin that molds with the immense pressure.
There are not many mammals that can be found this deep, but sperm whales, with their large, pressure-resistant heads, are often found in this zone, hunting squid, although, as mammals, sperm whales are not permanent residents of the zone, and will need to return to the surface for warms and oxygen.
Abyssopelagic Zone: Life in the Deep Darkness
Below the bathypelagic zone, extending from 4,000 down to 6,000 meters (13,123-19,685 feet), the abyssopelagic zone, also known as the abyssal zone, gives way to some of the most unique creatures on Earth.
Organisms like the ethereal gulper eel and the enigmatic tripod fish have evolved to capture prey and survive in conditions of constant darkness, freezing temperatures, and extreme pressure.
Three-quarters of the deep-ocean floor area lies in the abyss, which gets its name from the Greek word meaning “no bottom,” as the ocean was believed to be bottomless.
Life in the Abyssopelagic Zone
When we get down to the abyssopelagic zone, life becomes extremely sparse.
Giant squid, dragonfish, tubeworms, and a variety of invertebrates, which include sea spiders, can be found freely floating or meandering through this zone in constant hope for a meal.
Larger animals, apart from squid and jellyfish, are not common at these depths, although some shark species, such as the cookie-cutter shark and the frilled shark, can be found inhabiting this habitat.
Hadalpelagic Zone: The Deepest Depths
The Hadalpelagic zone extends to the deepest depths of the ocean. This zone spans from 6,000 meters to the seabed, with its deepest point reaching 10,994 meters (36,070 feet) in the Mariana Trench.
Despite its constant near-freezing temperatures and crushing pressure, life continues to make its way, even in the challenger deep, where single-celled organisms called foraminifera, a type of plankton, have been found.
Some fish have also been found in some of the deepest points of the ocean, sometimes below 8,000 meters, namely, in the Puerto Rico Trench.
Benthic Zone: The Underbelly of the Zones of the Ocean
The benthic zone describes the seafloor or bottom-most area of the ocean.
This can range from the floor of the intertidal zone through to the deepest part of the Oceanic Zone.
The seabed, or benthic zone, presents a wide variety of underwater landscapes such as the continental slope, continental shelf, abyssal plains, oceanic trenches, volcanic islands, and seamounts.
As the benthic zone spans through all other zones, the life, light, pressure, and life of the seafloor drastically change according to location and depth.
FAQs
How do creatures in the mesopelagic zone adapt to minimal light?
Bioluminescence and large eyes with special adaptions are common in mesopelagic inhabitants. This helps them navigate the low light of the Twilight Zone.
Why are coral reefs primarily found within the neritic zone?
Coral reefs flourish in the neritic zone due to the ample sunlight and a steady temperature, which is necessary for the photosynthesis of coral’s symbiotic algae.
What drives the tides within the intertidal zone?
The gravitational tug-of-war between the moon and Earth’s oceans causes tides. As the moon orbits, its gravitational force creates bulges on the ocean’s surface, resulting in the rise and fall of tides.
Do human activities impact ocean zones?
Deep-sea mining operations can disturb fragile ecosystems in the abyssal and hadal zone while overfishing in the neritic zone can disrupt marine food chains.
Furthermore, pollution, including plastic waste and chemical runoff, can harm marine life across all zones and degrade habitats.
