Hell as Habitat, part 3

Image: Dr. Bob Embley, NOAA

By now we know a lot about the hydrothermal vents and some of the weird creatures that occupy them. How they keep warm by the heat of volcanic water and are fed by bacteria that have learnt to make sugars out of stuff that usually kills everything. It's all very impressive. Sometimes, though, it's the sheer numbers that make your jaw drop.

We can see that deep sea mussels can cooperate to make an utter spectacle of themselves. Who else wants to outrageously flaunt their ability to survive Earth's most hellish habitat?

Image: NOAA

A Cast of Crabs
Who knew there were pigeons in the deep sea? Looks like they're as messy down there as they are up here! Take a closer look and you will see that what appears from afar to be a million dollops of excrement is in fact a million crabs.

This is Cyanagraea praedator, one of the bigger deep sea crabs with a carapace width of up to 12 cm (4.7 in). They are found on the East Pacific Rise at depths of around 2,600 m (8,530 ft), where they feast on worms and the young of other, smaller crabs. I wonder if those other crabs chase them down, menacingly snapping their claws. It could be like West Side Story. 990,000 crabs chasing 500,000 rival crabs, turning a corner and finding 1,000,000 rival crabs. I'd watch it...

Image: NOAA Okeanos Explorer Program

A Bed of Clams
I look at this scene and I can't help but think of those tracts of land next to railways that get full of litter. Those tend to be a bit more colourful and plasticy. A lot more brand names, too. Like one, big, non-ideal advertising solution. Here it's all white because this is Calyptogena magnifica, a kind of deep sea clam. They reach about 26 cm (10.2 in) long and are particularly fond of areas with lots of hydrogen sulphide. You'll see why if you savagely (or carefully):

• rip open their shells. The soft bits inside are red.
• rip open their flesh. The gills are swarming with bacteria. 
• rip open their cells. There's weird haemoglobin inside.

That's right! This clam absorbs oxygen and carbon dioxide from the water. Special haemoglobin allows them to take in hydrogen sulphide, too, without getting poisoned to death. This stuff is passed on to bacteria in the gills who can make sugars from it, which the clam then subsists on. Not as bad as a massive heap of rubbish, but also in a way a lot worse...

Image: R. Zierenberg

A Smack of (Stalked) Jellyfish
Stalked Jellyfish! Those weirder-than-weird jellyfish that live attached to plants and rocks. Most of them are tiny and live in shallow waters, Lucernaria janetae is a little different.

They live in hydrothermal vents on the East Pacific Rise, attached to rocks by a stalk (peduncle) 6 cm (2.4 in) tall. The umbrella (calyx) at the top is the same height and is formed of 8 tentacles, each topped with a burst of 100 or so mini tentacles. With these they capture their prey, mostly amphipods.

L. janetae completely dominates the vent sites they occupy, expanding to huge numbers and becoming the primary (non-teeny-tiny) rulers of their domain. The "big fish", basically. It's strange to think of the pretty little Stalked Jellyfish becoming the big, bad boss of the neighbourhood, but there you go.

There's also a mystery. Adult Stalked Jellyfish are sedentary. Larvae crawl about like slugs. So how have they managed to get themselves to numerous sites miles and miles apart?

Image: NOAA Okeanos Explorer Program, MCR Expedition 2011

A Troupe of Shrimp
I can't be precise, but I think this is ca. a million, billion shrimp. They're in the genus Rimicaris and come from the Mid-Cayman Rise in the Caribbean. They have appendages in their carapace that provide a surface for growing chemosynthetic bacteria that feed on hydrogen sulphide. The shrimp then eats the bacteria. It's a kind of farm on their back.

Also on their back is a strange eyespot that is thought to detect heat coming from the vents. It may seem like they are well provisioned with a backpack full of food, but stray too far from the vents and the bacteria will soon die. Something tells me these shrimp need no survivalist advice from the likes of me.

Image: JAMSTEC

A Group of Sea Anemones
There doesn't seem to be a collective noun for Sea Anemones, which might indicate how strange it is to see so many of them together. It's Mariactis cf. bythios, ghostly white and festooned with tentacles for capturing miniscule prey. They look fairly normal otherwise. Which is actually a huge achievement for something living in the deep sea. Jeez, where's the medal for contributions to "looking fairly normal"?

jobert2kx

Image: Wikipedia

Another Cast of Crabs
Aaaah! Breathe in that fresh, alpine air! Or have we stumbled on the fabled Popcorn Kingdom? Neither. It's a gigantic mass of decapods of the genus Kiwa, closely related to the Yeti Crab, and found at the bottom of the Southern Ocean. The bottom of the bottom.

The Yeti Crab had hairy arms and hairier pincers, but this Kiwa has a dense covering of hair on its ventral surface. A hairy chest, basically. Just like REAL men! It's covered in bacteria that the crab can eat when it's not scavenging from the floor. Just like REAL men!

The biggest and hairiest are found closer to the vents with all the heat and chemicals. Juveniles and egg-carrying females are a little further away in cooler waters. This seems to suggest that moving just a few feet from a vent has a drastic effect on how much bacteria you can cultivate on your belly. At last! Useful, timely advice!

All in all, it's a lot like life. The fresh, alpine air is actually boiling hot, poisonous water and the popcorn is hairy and covered in claws and bacteria. All you can really do is walk away from the vent. :(

Image: NOAA Vents Program

A Clew of (Tube) Worms
Alright, who's been dreaming of Tube Worms? 'Cos it's come true with not just a field, but rolling hills of tube worms. They're probably some kind of Siboglinid, annelids that lack a mouth or gut and gain their food from symbiotic bacteria. They live attached to the ground and secrete a chitinous tube around their body. Most of them have a diameter of a few millimetres but a length of several metres! They might even have roots that delve into the substrate to absorb sulphides for the bacteria. In the deep sea, this is as close as you can get to plants. Seriously, give those Sea Anemones a medal.

Image: NOAA Ocean Explorer

A Seething of Eels
You may have noticed that everything we've seen so far has been an invertebrate. It seems that backbone is a terrible liability in the deep. But there is at least one fish who fights the vertebrate's corner, crushing the crabs whacking the worms, muscling in on the mussels: Dysommina rugosa, an eel with its very own city.

D. rugosa is 35 cm (1 ft 2 in) long and can be found in tropical waters of the western Atlantic and Pacific oceans. But they are particularly abundant in a specific volcanic cone in the crater of a volcano in Samoa.

The volcano is Vailulu'u, rising from a depth of 5,000 m (16,400 ft) to 600 m (1,970 ft). The crater inside drops to 1,000 m (3,280 ft) and in its centre is Nafanua, a miniature volcano that rises to a depth of 700 m (2,300 ft).

Nafanua didn't exist in 2001 but it did in 2005. Already the hydrothermal vents there were colonised by so many of these eels that it was named Eel City. They took the place over! There are scarcely any crustaceans or other invertebrates to be found.

You might expect there to be Eel cars on Eel roads, fancy Eel shops selling locally sourced Eel food and an Eel mayor involved in Eel scandals in the Eel news. But there isn't. In fact, it's more like an Eel Hostel. They really just rest in the nooks and crannies. They even have to leave to find food, probably feeding on crustaceans swept up by the currents.

Surrounding Eel City and the rest of Nafanua is the Moat of Death, formed by the nastiness that oozes from the volcanic cone. It's full of the corpses of fish and squid, the bacteria that eat them and bright red bristle worms who eat the bacteria. A food chain of death, surrounded by death, a horror but also a really cool backdrop for Eel City.

So if you ever find yourself lost in the deep sea, check out Eel City. Show them your backbone and they might just let you stay the night.