A survival guide to the deep ocean: What you need combat the dark
Deep below the surface waters of the world’s oceans is a habitat that only the hardiest and most well adapted organisms can survive. The deep ocean is defined by the area where the ocean becomes void of light. This occurs at around 1000m below the surface. Not only does the deep ocean have no light it also has crushing pressures and toxic vent systems. All these conditions make the deep ocean a difficult and unforgiving habitat to live in. despite this there is wide range of organisms that, not just inhabit, but thrive in the deep!
The organisms that inhabit the deep ocean are able to survive due to a range of different adaptations. These adaptation can range from the eye; to aid with vision in the dark, bioluminescence; to attract prey and deter predators and even behavioural adaptations; which allow organisms to feed more effectively. Throughout this article we will go through these different adaptations that allow deep ocean organisms to survive and live successfully in this extreme habitat.
Many organisms in the deep ocean have eyes that are adapted to allow them to see in the darkness of the deep. The Escolar for example (Lepidocybium flavobrunneum) has enlarged eyes, giving them much higher optical sensitivity. To aid the Escolar in low light vision the eyes also have increased layers of rods. This allows the eyes to be more sensitive to light. In the low light conditions of the deep ocean this allows the Escolar to see potential predator and prey species where other organisms may not.
Another example of eye adaptations is the deep-sea squid Teuthowenia pellucida. As with the Escolar, the squid also has larger eyes that allows more light to enter the eye, however, the deep-sea squid also has increased concentrations of photoreceptors on the outer region of the eye. These photoreceptors react to light that enters the eye and allows the squid to process images that appear in the aphotic deep ocean. These images, which are processed in the brain of the squid, could potentially be prey or predator species.
In being able to visualise potential predator and prey species in the deep ocean can give an organism an advantage over others that may not be able to see in the darkness. Organisms that can visualise their prey or predators can be more successful in catching prey and avoiding predators.
Bioluminescence is an adaptation that is utilised by many deep ocean organisms. This is the production of light in the in organisms via two distinct methods. The first of these is the production of the light by bacteria which live inside the cells of an organism. These bacteria have a symbiotic relationship with the organism. The organism will provide the bacteria with sugars from their cells, from this the bacteria can provide the organism with their light production. An organism can use these light producing bacteria to produce light in their cells. The second method of light production is the use of photophores. Photophores are non-bacterial bioluminescence. These are cells that are present in an organism that are controlled by hormones. There could be a potential advantage for photophores over bacterial bioluminescence due to there being no trade off of sugars to the bacteria for the bioluminescence. There is, however, an energy cost associated with photospheres due to the use of hormones.
Bioluminescence can be used by organisms to either attract prey or deter predators. The deep sea angler fish Melanocetus murrayi uses bioluminescent bacteria in a light organ on its head to attract prey species. This bioluminescence is flashed on and off by the angler fish to attract prey species. This flashing can represent smaller organisms such as copepods, which are prey species for organisms that the angler fish feeds on. The lure that is used attracts prey close to the angler’s mouth which than allows the angler to strike and capture the prey item.
On the other hand prey species can also use bioluminescence to deter or confuse predators. Prey species can use red bioluminescence in order to essentially make themselves invisible to predators! This is due to there being no red light in the ocean beyond 15m. In the euphotic zone of the deep ocean, any organisms that are red will not be seen by predator species.
There are several organisms in the deep ocean that change their behaviour in order to allow for more effective feeding. The behaviour that is mainly present in the deep ocean is the vertical migration of organisms in the water column. This migration of larger organisms is due to the vertical migration of plankton species. As the plankton move upwards in the water column, larger deep ocean species follow and take advantage of the more abundant food source in the bathypelagic zone. This behaviour allows deep ocean species to find a food source which could otherwise be limited in their usual habitat.
Food can be very limited for many deep ocean organisms. This means that when a potential meal appears for an organism they need to take it. The gulper eel (Eurypharynx pelecanoides) has adapted its mouth in a way that allows it to capture almost any prey items even if the species is larger than the eel. This larger mouth leads to the eel being able to capture a wide variety of prey species, meaning that it can feed nearly every time an organism appears for the eel. This will lead to an increased chance of survival for the eel.
To survive in the deep ocean you will need to be able catch prey at every opportunity that swims along, at the same time being able avoid being eaten by your predators. Organisms of the deep ocean, like the Escolar, the angler fish and gulper eels have mastered these techniques with multiple adaptations allowing them survive in the pitch blackness which is the extreme deep ocean.