Researchers have discovered that what appeared to be the ocean floor is actually a dense layer of fish known as the Deep Scattering Layer (DSL). These fish swim up to the surface at night to feed and are mostly made up of phytoplankton.
During World War II, scientists were experimenting with new technology called SONAR to aid in the war effort. SONAR had previously been used during World War I and was particularly useful for detecting submarines.
However, during their tests, scientists noticed something strange: the ocean floor was much shallower than expected, only a few hundred meters from the surface. Even more peculiar was that the ocean floor seemed to rise to the surface at night. This raised questions about what was truly happening at the bottom of the ocean.
To understand this phenomenon, we need to learn about how SONAR works.
Submarines were a major threat during World War II (Photo Credit: Everett Collection/Shutterstock)
What is SONAR?
SONAR stands for “SOund NAvigation and Ranging” and is a system used to locate objects underwater. It works by emitting sound waves that bounce off objects and measuring the time it takes for the echo to return. This information helps create a map of the underwater objects and landscape. More information about SONAR can be found in this article.
SONAR works by emitting sound waves and analyzing their reflections (Photo Credit: Akarat Phasura/Shutterstock)
During World War II, SONAR was crucial in detecting submarines, and it is still used today for mapping the ocean floor and finding shipwrecks.
SONAR is not only useful for humans but also for animals. Dolphins and whales use SONAR to locate their food. Similar to how the technology worked on ships during the war, these marine mammals emit sounds that bounce off objects, including fish, allowing them to determine their location.
An Ocean Floor Composed of Fish
The apparent shallow ocean floor that becomes shallower at night is not the actual ocean floor, but rather a dense layer of fish known as the Deep Scattering Layer (DSL).
The DSL consists of various sea creatures that have evolved to live in the high-pressure, low-light environment 300-500 meters below the sea’s surface. This unique environment gives rise to fascinating creatures like the lantern fish.
This is an image of a lantern fish that emits its own light. These fish have evolved to glow because they live in areas where there is no natural light. The absence of light in these areas makes it difficult for predators to spot them. However, the purpose of glowing in the dark is still not fully understood. There are various theories explaining why these fish have this ability, ranging from attracting prey to deterring predators. The patterns in which the glowing parts of the fish are arranged suggest that the lights help with camouflage.
Scientists have observed that the fish in the deep-sea zone known as the Deep Scattering Layer (DSL) move closer to the surface at night. This behavior is puzzling because it contradicts the idea that darkness provides safety for these fish. One possible explanation is that the darkness in the deep sea also means there is very little food available. In any ecosystem, the food chain starts with primary producers, which convert light, water, and other compounds into food. In the ocean, the primary producers are mostly microscopic organisms called phytoplankton, which need sunlight to survive. These phytoplankton float near the surface, so the fish in the DSL swim up to the surface at night to feed on them. This daily migration is known as Diel Vertical Migration (DVM).
The DSL is vital to marine ecosystems as it supports a diverse range of marine creatures and plays a crucial role in their food chains. The migration of fish in the DSL allows phytoplankton to reproduce and replenish their populations, ensuring a sustainable food source. However, studying the animals in the DSL is challenging due to their deep-sea habitat and limited surface presence. There is still much to learn about the behaviors and reproductive habits of these fish. Further research is needed to understand this part of the ocean and develop effective methods of studying it.