Secrets of the Ocean’s Mysterious Mesopelagic Zone

Scientists have designated distinct aquatic layers within the ocean, known as zones, which are determined by the amount of light that reaches a specific area. These zones vary spatially and function as helpful frameworks for exploring and understanding how these ecosystems work.

The abyssal zone is the deepest zone, found in the depths of the ocean floor. It is situated precisely between the sunlit surface zone and the dark deep-sea zones, for those who are familiar (or interested) in zone terminology. The twilight zone is a subdivision, the central portion, of the open water zone.

The patterns and movements of the ocean, as well as the carbon cycles, are still being studied to uncover answers. These zones also hold mysterious and alluring characteristics, with some being well-known while others remain tantalizingly unknown. Each zone and layer of the ocean contains various creatures and unique features. The term “midwater” is used to describe any area of the ocean that is below the surface and above the seafloor.

Andrey Armyagov/

Characteristics of the Mesopelagic “Twilight Zone”

It appears that when we contemplate what it feels like to be in a different planet, we could certainly imagine a phenomenon where deeper waters slurp around in a way that feels like an alien environment. This poetic term seems to encompass the unnerving magnetism that we feel when pondering what it feels like. It is a layer of water stretching around the entire globe. The middle zone of the ocean, known as the mesopelagic zone, is sometimes referred to as the twilight zone because it is similar to the time of day when darker and lighter areas can be found between the ocean’s darker and lighter areas.

The zone where there is no light, known as the mesopelagic, starts below the surface of the ocean, at depths ranging from 600 to 3000 feet. Only 1% of the original light is present in this region.

Subsequently, we will delve into the extensive array of organisms that inhabit this portion of our biosphere. It encompasses 20% of the total volume of the world’s oceans and 60% of the Earth’s surface, despite its enigmatic nature. This oceanic stratum is incredibly vast.

The stratification of ocean layers causes changes in temperature, density, and salinity. These changes include significant and sudden shifts, which occur in the mesopelagic zone, where the area is characterized by drastic and sharp changes.

Oceanographers today utilize various methods to study deepwater ocean currents. Similar to how armies in WWII used different ways to communicate over long distances, they would propagate and refract sound waves. This deepwater zone, known as the SOFAR channel, is where sound travels incredibly slowly at the lowest levels of the water. Additionally, salinity and temperature also have a unique acoustic effect.

Carbon Cycle and Carbon Pump

The mesopelagic zone also plays a crucial part in oceanography, as it is a critical contributor to the carbon cycle in the ocean. It is often referred to as the “biological pump,” highlighting its significance in the Pacific and Atlantic oceans.

The particulate organic carbon (POC) is packaged and decomposed by migrators, such as mesopelagic fish and microbial organisms, in the mesopelagic zone, or it is carried by migrating animals. This cycle begins in areas where there is sufficient light for photosynthesis to take place, primarily in the surface euphotic zone. Subsequently, the organic carbon sinks into the mesopelagic zone.

Mesopelagic Organisms

These ecosystems hold both artistic and scientific inspiration in their depths. This impulse is not limited to a single element but rather serves as a means of new discovery in both human exploration and imagination. Students and scientists alike follow theories and hypotheses with vigorous curiosity. Deep-sea creatures of the mesopelagic zone often show up in different cultures’ mythology, literature, movies, and visual art, defining important aspects of these cultural expressions. However, it is the microbial organisms and carbon cycles that play a foundational role in this zone, even though it is the sea creatures that truly capture people’s attention.

These are merely a handful of instances of mesopelagic ecology: They reside in a habitat where the force attains 1,500 pounds per square inch. They have adapted to survive in extremely cold temperatures. Animal dimensions in this region vary from minuscule to some of the most gigantic on our globe. However, there exist numerous other lesser-known creatures that float and move in these waters. The mesopelagic zone is a vast, compact congregation of organisms you will identify, such as jellyfish and squid.


In the world of animals, invertebrates are categorized as an “artificial division”. This category encompasses 95% of animal species that lack a spinal column. Within the mesopelagic zone, invertebrates can be found floating, swimming, migrating, and simply existing.

Additionally, within the region reside gelatinous creatures, such as jellyfish and squid, as well as larger crustaceans and copepods (tiny crustaceans). Among the food options are phytoplankton, which prey on krill, such as zooplankton, including various types of plankton.


When it comes to swimming, the mesopelagic zone is their territory. Naturally, only humans, who are an entirely distinct kind of organism, are vertebrates.

The fish has a wide and full mouth with spiny teeth, but it is small in stature. The appearance of the fish fits right into the suspenseful show of the same name. It is a true “twilight zone” fish. It is possibly the most abundant vertebrate on planet earth, numbering in quadrillions. Examples include the nightmarish bristlemouth and lanternfish.

Oceanographers state that there are still numerous species to be found in the region.


In such a dim and consequently limited-food habitat, living beings have adapted in ceaselessly captivating manners to endure. Certain areas in the mesopelagic zone do receive some illumination, although it is insufficient for photosynthesis, as mentioned earlier.

Particularly in the vast expanse of the open ocean, it remains a perplexing event, regardless of its perceived frequency. This is a rather prevalent occurrence in the marine environment, occurring on the planet’s surface as well (like luminescent mushrooms and fireflies in the midwest). Bioluminescence is the term employed to characterize organisms that generate their own illumination.

Luciferin is a substance called oxidized, and it undergoes a chemical reaction when light shines. These creatures produce light through symbiotic bacteria and light-emitting cells called photophores.

This is a clever adaptation, where the furthest penetrating water appears blue in color. It is a form of communication between animals, with the most common light emitted by these animals. It can be used for intraspecific communication and for offense and defense. Examples of creatures that glow in this way include planktonic species, jellyfish, comb anglerfish, and deep-sea creatures.


Daily Vertical Migration

This serves as a reminder that it is intricately connected and has massive impacts on the entire globe, whether you are particularly interested in large vertebrates or prefer to investigate more information on myctophids and the biochemistry of these zones. We previously discussed how this is tied into the carbon cycle, with organic particles being transported deep into the ocean. Species travel up and down between the euphotic and mesopelagic zones, transporting organic particles. However, it is important to note that certain species in the mesopelagic zone undertake a crucial process known as vertical diel migration.

The Enigmatic “Deceptive Base” Of The Sea

Less than 10% of the world’s oceans have been explored. There are still many unknowns in the vast universe. We have some knowledge about the fascinating creatures in the mesopelagic zone.

At dawn, the Navy ships known as “the phantom” arrived at the bottom of the ocean. As they descended, the signal they emitted reflected off the various types of surfaces on the Earth’s floor. During the night, this phenomenon, which was a global indication of a substantial substance, fell on the wide surface of the ocean floor. Journalists and scientists soon realized that this phenomenon was being reported all around the world. It was then understood that dense chunks of the Earth’s floor had accumulated on the ocean floor, resembling sunken islands. Operators using sonar technology detected this large mass on the ocean floor before we even understood the concept of vertical diel migration.

We uncover even more mysteries by pursuing curiosities and questions. Before returning to deeper areas, we discover that as the night falls, the water temperatures rise, revealing a diverse range of marine creatures such as jellyfish, shrimp, and fish. This thick layer of marine life is known as the “deep scattering layer.” We now understand that these islands are not sunken, but rather a result of the scattering layer in the deep.

Mesopelagic Climate Variations

As a result of human influence, this deep dark zone is also undergoing changes, and we possess a wealth of evidence regarding the abundance of enigmas present in the mesopelagic zone. Climate change and the subsequent predicament have affected every corner of the world.


We have explored every ocean basin, including microplastics and plastic. We have found record levels of pollution, but we are not exactly optimistic about the track. We see our own floating garbage on the surfaces of the earth’s waters, but pollution breaks down and sinks to lower levels.

In a study conducted in 2018, it was revealed that 73% of fish samples in the North Atlantic contained consumed plastic. It is alarming that plastic has now become a part of the food chain, affecting not only the creatures living in the ocean but also the entire ecosystem. The ocean’s food web is a complex system, with organisms and creatures interconnected in ways that bring them closer to the surface. As migratory creatures travel upwards, they mix with phytoplankton and zooplankton, ingesting plastics and making it a part of their meals.

Effects of Temperature and Non-Uniformity

Rising temperatures are causing major shifts in the ecosystems both below and above the surface of the ocean, putting added strain on biodiversity. Plastic usage and pollution are significant issues that need to be addressed in order to tackle these challenges.

The middle layer of the Arctic Ocean will experience varying conditions compared to the area near New Zealand. The extent of these changes is expected to rely on the particular context and circumstances of each location. The exact transformations that will occur in the middle layer of the ocean in response to these changes over time remain uncertain.

The predictions and climate models often do not include a staggering number – between 12 billion and 5 billion tons of carbon dioxide each year from the atmosphere, cycling through the mesopelagic zone.

One of the least-understood areas of our planet could also be the most important. We still don’t know much about it. In other geographies, the opposite might be true for fish biomass. The web of food might thrive with higher trophic efficiency and temperature-affected metabolisms. Researchers suggest that the biomass of this zone could potentially increase due to a surplus of other nutrients and food in the warmer waters.

Fishing Traps in the Enigmatic Depths

You are not alone, this idea gives you existential chills. In conjunction with the ever-growing demand for fish from our increasing human population, and the climate crisis, look to the mesopelagic as the next frontier for fishing powerhouses in the world.

Pakistan and Norway have issued licenses for fishing vessels to open Pandora’s box and follow suit to global efforts. However, the waters, which have already been pillaged, are plagued with unsustainable fishing practices.

Unleashing humanity’s insatiable desire for horror stories upon the environment is unnecessary. However, there is a sustainable way to process and can fish that can greatly benefit global communities by providing nutritious and long-lasting food without depleting fish populations, which serve as their source.

The collaboration of scientists and oceanographers, backed by scientific knowledge, adds immense urgency to understanding this zone with the hope of delving into its depths. However, due to the numerous uncertainties surrounding the delicate ecosystem of the mesopelagic, we cannot truly comprehend what “sustainable” means in this food web.

It is quite an achievement to combine our determination for advancement with a sense of modesty towards the concepts that are still beyond our comprehension. We have undoubtedly gained knowledge from the mistakes made in different regions of our world.

Request for Action

Marine ecosystems rely on this. It is crucial for us to take responsibility as individuals while coordinating initiatives within our communities and governing institutions to contribute to the well-being of the planet we cherish and safeguard the enigma of the mesopelagic zone.

Amidst the realm of twilight, not the ocean floor or shallow businesses, a major portion of the efforts thus far has been dedicated to implementing sustainable practices that surpass the authority of individual nations. The United Nations Law of the Sea Convention has already initiated efforts to advocate for predominantly unregulated frameworks for offshore fisheries. One particular matter that we can rally behind is the contribution.

We certainly have cut out work for us. According to NOAA, more than 80% of our oceans are unexplored, unobserved, and unmapped. This is a highly inaccessible area without massive amounts of funding for continued research. It is important to find answers on how much these animals contribute to the global carbon cycle. We need to know more about the intricacies of the food web. There are still big questions remaining about the life cycles of undiscovered species. We can write legislation to pass and promote the protection of these areas. We need to be better equipped to know more about the phenomena and animals in the mesopelagic zone.

To Sum Up

There are definitely actions to take and battles to wage on behalf of the oceans, whether you live in a landlocked, concrete jungle of glass and steel or in a place where you can smell the salty sea air. There has never been a better time to consider studying oceanography in order to funnel resources towards the exploration and lobbying efforts of these serious issues by our representatives.

The stakes are high, as deep as the ocean floor, but our efforts in organizing might be effective in lifting up the scattered fish layer into new realms of sustainability and balance for future generations.