In science classes starting even in elementary school, most of us learned about the layers of the Earth (core, mesosphere, asthenosphere, and lithosphere [core, mantle, and crust]) or the atmosphere (troposphere, stratosphere, mesosphere, thermosphere, and exosphere [aka space]). Well, the ocean has layers as well (like an ogre or an onion… but not a parfait, Donkey). There is a bit of a difference.
If you think about it, pretty much every form of life on land lives in a very small zone right on the surface. Even birds, though they can fly, live in trees, bushes, or on the ground. The ocean is a truly 3-D environment; there are critters living at every level, right at the surface, on and beneath the bottom, and anywhere in between.
Benthic refers to the bottom of the ocean, from where the waves meet the beach to the deepest part of the ocean. Animals that live in this zone are called benthos and can range from crabs scuttling through the surf or just-discovered creatures at the bottom of the Mariana Trench. This zone covers a huge range, the entire ocean floor, and is divided into the littoral/sublittoral (intertidal/continental shelf), bathyal (continental slope), abyssal (abyssal plain), and hadal (ocean trenches) . Some examples from the deep sea are: hydrothermal vents, cold seeps, hydrothermal seeps, and brine lakes (yep, lakes on the bottom of the sea).
Pelagic – the word literally means ‘open sea’, and that’s exactly what this zone is; all of the water from the surface down to the ocean floor. The pelagic zone can be divided further into the photic zone (where light reaches) and the aphotic zone (with little to no visible light). 90% of the ocean’s life lives in the photic zone (also called epipelagic [pronounced epi- (like epi-pen) – pelagic]) and this is also where the ocean’s primary producers live and photosynthesize. When there is no longer enough light for these organisms, like algae and phytoplankton, to photosynthesize you have reached beginning of the aphotic zone. Less than 1% of sunlight reaches the upper layers of this zone and as you travel down to the bottom of the ocean you have now crossed over into…
… The twilight zone begins the strange creatures of the deep with big eyes, scary teeth, strange bodies, and – the coolest part – bioluminescence (organisms making their own light). Things just get weirder the further down you go. You start with the mesopelagic, bathypelagic, abyssopelagic, and finally the hadopelagic. As you travel through these zones, organisms have to deal with no light, intense pressure that would crush a human, and wide expanses with little food or prey. These challenges lead to some pretty cool adaptations – check them out below.