The deep-sea benthos

Unreachable to most humans, the deepest depths of the ocean hold endless wonders from the totally adorable to really creepy, from the hot to the cold, from the dark to the—no, all dark. Unless you meet one of those creatures that can make their own light.

Chapter 1: The deep-sea benthos

The deep-sea benthos is used to describe the areas near and within the ocean floor, though we’re excluding the coastlines. I mean, deep, right?

The conditions down in the deep are anything but inviting. Immense pressures, near-freezing temperatures—unless you are near a hydrothermal vent where water of up to 400 degrees Celsius spews out—and just a whole lot of nothing. Though seeing that whole lot of nothing isn’t that easy without light, I guess.

Deep-sea environments are dominated by thick, depositional, soft sediments, so mostly sandy mud stuff. Structures and features like the oceanic ridges and trenches we talked about in the introduction episode interrupt this vast nothingness.

But the lack of structure does not mean there is a lack of life down there.

Chapter 2: What lives down in the deep?

There are many ways to classify the biodiversity down there. Every structure has their own communities, biodiversity, and kinds of life. Add regional variation—and the fact that there’s probably a lot more down there than you think.

You could go by size, dividing them into meiofauna, macrofauna, megafauna, and the like, though, as I’m usually not interested in anything that isn’t at least macrofauna… well, maybe not the right division for me. Also, some organisms will be considered temporary meiofauna while they are larvae and other tiny non-adults, then later become macrofauna.

An alternative way would be to look at where these organisms life. Infauna includes animals that live within the sediment, so inside the actual seabed, while epifauna includes the organisms on or above the surface.

The little things (aka meiofauna)

A lot of little things (aka meiofauna) exists in the deep sea. Nematodes, so round worms, are not just one of the most abundant animal species in the deep-sea but anywhere on earth. Copepods, so tiny shrimpy-looking creatures are also pretty much everywhere. They are also a big deal near the ocean surface, where they are part of the plankton crew.

The little-but-visible things (aka macrofauna)

But enough about the little things. Let’s talk about the macrofauna, instead. Unfortunately for worm-bored me, the most abundant species include another worm, but, to be fair, it’s the polychaete worms, which are pretty damn cool, because of their characteristic bristles.

By Jenny – Flickr: “Aliens” movie star! CC BY 2.0,

But still, worms. I haven’t caught that obsession bug yet. Though, considering how much I like mushrooms and soil, I’m sure I’ll get there at some point. One obsession at a time.

Other than the polychaete worms, there are many more small crustaceans (though obviously bigger than the copepods) and a shitton of mollusks.

The larger things (aka megafauna)

Okay, bigger still, please. The deep-sea megafauna is no less diverse than the smaller creatures. You’ll find echinoderms, cnidarians, porifera, and fish, alongside many others.

If you don’t remember what all of these groups are, here’s a very quick recap including some links to the original episodes about the groups:

Echinoderms: Sea stars, urchins, cucumbers and the like.
Cnidarians: Jellies, corals, anemones and the like.
Porifera: Sponges.
Mollusks: Mussels, clams, snails, octopuses, nautiluses, squid, cuttles, and the like.

What’s even cooler (and sounds even weirder to most people) is that stony corals even form reefs on the seabed. True ecosystem engineers, right? They might not build the massive structures you know from the near-shore reefs, but they fulfill a similar function by providing a home and hiding place for many other organisms.

But wait, corals in the deep sea don’t make any sense, do they? Don’t corals get their energy from their photosynthetic allies, the Zooxanthellae?

Photosynthesis logically doesn’t make any sense in the deep sea where light is a rare to non-existent resource. The deep-sea corals are also typically symbiotic, but their allies take advantage of chemosynthesis instead.

We’ve talked about the black and white smokers last time, vents in the sea floor that add especially sulfuric compounds into the water. Those sulfuric compounds are the sun of the deep-sea, allowing bacteria to transform that stuff into energy and oxygen.

This is, by far, not the only adaptation of the deep-sea benthos, of course. All groups are well-adapted to the harsh conditions at depths that result from a lack of sunlight, chilly temperatures, and extreme pressures. Nonetheless, there are still a lot of uncertainties about the biogeochemical nets of these communities. I’m excited to see what the future reveals. Every submarine dive I watch seems to reveal new creatures and facts. After all, we have seen more of the moon’s surface than we have seen of our oceans.

The deep breeds freaks and giants, but don’t judge them for it. They are merely adapted to the world they live in. To quote Stone Sour, “it’s just a different scene; it’s just different from what you’ve seen.”

Chapter 3: Whalefall

One very cool feature of the deep-sea that most people have never heard about is whalefall, and it’s exactly what the name suggests: whales fall. Well, when a whale dies, they usually don’t get eaten fully at the surface, so the bulk of the whale sinks to the bottom of the ocean as whalefall. This creates a temporary ecosystem of devouring creatures around the carcass.

While whales are vastly more important while they are alive and pooping (see our recent episode on whale poop and carbon sequestration to the deep sea), they carry a lot of carbon stored in their body down to the depths of the ocean. And while this carbon gets moved around a bit at the bottom (e.g. by other creatures feeding and pooping and such), it stays down there for quite a long time, helping keep more carbon away from the atmosphere.

While the whale is there, an entire community accumulates around the carcass from bacteria and worms to larger animals that don’t say no to a chance meal of yummy whale blubber.

Chapter 4: The obligatory doom-and-gloom detour into reality

I’m gonna stop apologizing for adding doom-and-gloom into the series. If you want to know why, read this article on my website.

The deep-sea is subjected to a fucking plethora of adverse impacts that can be traced back to human activities. There are direct impacts like the trash we have now found at the bottom of the very deepest trench in the ocean, the Mariana’s Trench, scraping fishing-gear over or even through the sediment, and messing up the seabed for deep oil and gas exploration and extraction, mining, laying infrastructure such as cables and pipelines, and so on. And while some of these activities are necessary for our global economy (fuck, I am starting to hate that word…), we need to stop putting humans above everything. Speaking of: indirect pressures like climate change and pollution add to the struggles of our deep-sea friends.

The problem is, instead of dialing down the destruction, we are now thinking about how to exploit the ocean for more and more resources.

Deep-sea mining for polymetallic nodules is not profitable yet, but it is the “yet” that scares me. If we start that, much larger portions of the ocean floor will be dredged up. And, remember, stirring up the sediment by bottom-trawling is already causing more carbon dioxide emissions than the entire airline industry.

Meanwhile, scientists want to shove more carbon dioxide into the ocean by forced sequestration, completely ignoring that the ocean is already doing all it can. Buffering our emissions is already causing and accelerating ocean acidification.

Protecting the ocean will be one of the major solutions to saving humanity. Instead of looking to the ocean for more-more-more, we need to start thinking about the future of humanity. The climate and biodiversity crisis are here, and we need to act now to affect change.

And that doesn’t mean protecting just the land or the coastal areas. We need to think about all parts of our planets and protect the deep sea, the soil, the forests, the waters, the air, all of it. From top to bottom, from warm to cold, from rich to poor, from far-gone to pristine. All of it.



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