Do the animals at the bottom of the ocean know it’s dark season?
Do the animals at the bottom of the ocean, that might never have been exposed to sunlight, notice the dark season as we do? It seems logical to assume that the polar night should go by completely unnoticed by them. But it doesn’t.
It’s impossible for us to overlook the dark time since we see the sun on a daily basis, but what about animals at the bottom of the ocean, who might have never in their lives been exposed to sunlight? It seems logical to assume that the polar night should go by completely unnoticed by these animals that live out their entire lives in total darkness.
As it turns out, even animals in the deepest reaches of the ocean feel the effects of the winter darkness. This is because of the way in which food is produced on our planet. All life on earth is carbon based, so all living creatures need carbon to sustain their bodies. Unfortunately, not any carbon will do, we specifically need organic carbon. This means that we cannot just eat carbon dioxide from the air. Instead, that inorganic carbon needs to be converted to organic carbon, which is not easy, and something animals cannot do that conversion. Green organisms like plants and algae can do it, but even they need an external power source to fuel the process. Usually the energy source is the Sun, so we refer to the procedure as photosynthesis. It is primarily through this process that organic carbon becomes available for all living beings, whether they are herbivores who directly consume the plants generating organic carbon, or carnivores, which eat the herbivores.
In oceans, photosynthesis can be problematic since sunlight only penetrates the top few hundred meters. The surficial, sun-exposed layer is a tiny fragment of the large water body that makes up an ocean, meaning that in most parts of the world’s oceans, photosynthesis is not possible. As a result, deep-sea animals have to rely on food trickling down to them from the surface, and naturally, the quantity and quality of food reaching the seafloor decreases the deeper you descend.
In the dark season, photosynthesis at the surface comes to a halt (though not completely), and the already food-poor seafloor becomes even more starved, and desert-like. One of the ways that deep-sea animals survive on the lean pickings of the polar night is by doing everything slowly and keeping their metabolic rates low. Less energy expended means less food needed. Seafloor animals also tend to be good at alternating between feasting and fasting, so sudden influxes of food can provide sustenance for a while. One of my favourite ideas is that deep-sea animals ride out the polar night by hanging out at ecosystems like hydrothermal vents and hydrocarbon seeps, where food production is powered by chemical energy from the earth, instead of sunlight, and is therefore not seasonal. Similar to that one restaurant that stays open during Christmas; these locations are oases within the desert of the deep sea and the polar night.
It’s hard to imagine that the dark season is life threatening for animals that have never experienced the sun in any shape or form. Maybe swallowing “Tran” (cod liver oil) is not the worst effect of the polar night after all.