Researchers recently explored hydrothermal vents in the Gulf of California, up to 4,000 meters deep. DW spoke with marine biologist Greg Rouse about what kind of creatures live down there and how they manage to survive.
Image: Rainer Dückerhoff
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Deutsche Welle: Mr. Rouse, In November 2018, your research team explored hydrothermal vent fields at Pescadero Basin, 150 kilometers off the coast at La Paz in Mexico. You brought back detailed maps of the place, high-resolution video via underwater robots and specimen of animals that live down there.But the first question is, of course, how can life exist so deep down in the ocean, where there is no sunlight?
Greg Rouse: There is a whole food web down there based ultimately on bacteria and hydrothermal fluids. Some microbes have evolved to gain energy from these chemicals, such as hydrogen sulphide.
Welcome to another world, deep down on the seafloor
Visit hydrothermal vents in this deep sea harbor and see the strange looking animals that thrive under pressure and in darkness. Researchers recently explored a vent field in the Gulf of California.
Image: ROV SuBastian/SOI
Welcome to Pescadero Basin
At a depth of 3,700 meters (12,000 feet), dozens of natural chimneys stick up from the seafloor emitting hot fluid at 290 degrees Celsius (554 degrees Fahrenheit). Over thousands of years, towers of lime have piled up. This is the hydrothermal vent field of the Pescadero Basin, about 150 kilometers east of La Paz in Mexico in the Gulf of California. A marvelous place!
Image: ROV SuBastian/SOI
Underwater robot ventures down
US researchers at the Monterey Bay Aquarium Research Institute discovered the deep-sea vent field at Pescadero Basin in 2015. A few months ago, a research team went back on board the Schmidt Ocean Institute ship ‘Falkor’ to explore this special place. They mapped the seafloor, recorded high-resolution video and brought back rocks and animal samples.
Image: 2018 MBARI
It’s all thanks to bacteria
Due to volcanic activity underground, hot water creeps out of the seafloor, containing chemicals such as hydrogen sulfide - a gas that smells like rotten eggs. It is extremely toxic to humans, but some bacteria can metabolize it and gain energy from it. Those bacteria thrive down here at Pescadero Basin and form these thick, fluffy looking bacterial mats.
Image: ROV SuBastian/SOI
Why Pescadero is special
The vents are buried in the sediment, so the hot liquid reacts with rocks before it escapes. Therefore, the liquid is clear (like you can see in this picture). At another type of vent called a 'black smoker', dark, metal-rich fluid leaves the chimneys instead. Pescadero harbors life quite different from that what was found at other vent fields explored previously.
Image: 2015 MBARI
Meet the residents
The vents are densely covered with tubeworms (Oasisia alvinae). These sessile invertebrates live in chitin tubes just a bit wider than their body. Tubeworms like this one were discovered in the 1970s at a vent field near the Galapagos. The researchers were amazed by how many of these animals live at Pescadero. They are literally everywhere.
Image: ROV SuBastian/SOI
Making use of bacteria
Oasisia tubeworms don’t have a mouth or a digestive system. Instead, the animals take up hydrogen sulfide and oxygen from the water with their orange-red plumes. They feed the nutrients into a bag filled with bacteria. The bacteria then generate energy for them. It works similar to the bacteria in our guts digesting food for us.
Image: 2015 MBARI
Quarrelsome scale worms
In Pescadero Basin, researchers found species they hadn’t seen anywhere else before. Like this iridescent blue scale worm, named Peinaleopolynoe orphanae. Across their back, they have thick discs that refract light - just like the wings of a butterfly. The researchers watched the creatures fighting with each other. They have big jaws which they can project during a fight.
Image: ROV SuBastian/SOI
A pink sock
This strange creature is called Xenoturbella profunda, but scientists often call it simply the “sock worm”. This turns out to be quite literal — they are just a bag with a mouth underneath. Scientists saw these strange animals gliding very slowly over the seafloor. They seem to feed on clams, as researchers found clam DNA inside their bodies. How they catch and eat their prey? Nobody knows.
Image: 2015 MBARI
Frequent visitors
Some animals — such as tubeworms, scale worms and Xenoturbella — live directly on the hydrothermal vents. Others, though, just float by, like fish or octopuses. Or this guy here, a siphonophore. It resembles a jellyfish, but it's not one. It’s more closely related to the venomous Portuguese man o' war.
Image: ROV SuBastian/SOI
Underwater lakes
Apart from animals and rocks, there is more to see in the Pescadero Basin. Underwater lakes like this one, for example. They develop when hot fluid gets trapped under rocks or within caves and cannot escape.
Image: ROV SuBastian/SOI
Who wouldn’t want to be a marine biologist?
An underwater-robot pilot on the ship steers the remotely-operated vehicle from vent to vent. Via a tether, the robot sends back data and high-resolution video footage to the surface. The researchers can thus see in real-time what’s going on down there. An awesome experience, for sure.
Image: ROV SuBastian/SOI
Alcohol kills beauty
The underwater robot has an arm with which it can pick up rocks and animals and bring them back to the surface. But most animals lose their colors and shape pretty soon when conserved in alcohol in the researchers’ lab. This for a example is a sea cucumber from Pescadero Basin, beautifully colored in life – not anymore.
Image: Rainer Dückerhoff
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There are a lot of free-living bacteria forming bacterial mats. Animals eat those, they are actually grazing on them. Then there are things like clams and tube worms — they farm bacteria inside their bodies. Most of the biomass down there comes from animals that have symbiotic bacteria in their bodies. It's very efficient and they are able to grow very large. And other animals eat them. Crabs, for example, prey on tube worms.
What fascinated you the most, down there at Pescadero Basin?
'Xenoturbella profunda' — we also call them purple socks or sock worms. They have a very simple body. They have a mouth underneath, and otherwise they are a bag, there is nothing else. There is no anus. They have no real brain. They have no kidneys. I've been working on them for 13 years and to see them alive and watch them was really exciting. We also found some crazy blue scale worms and watched them fighting with each other. So my immediate answer is those two things, but there's a lot of other things I want to study in the coming years. My students and I have years of work here.
The scale worm you mentioned is shiny blue – why this color when there is no light around?
We think it is an accident. They have a cuticle, a covering of the scales. It is probably quite thick and it is just an accident by the nature of the cuticle structure that it diffracts light, just like the wings of a butterfly. The smaller worms are pink and when they become bigger, they get blue, but we don't think it has any advantage. The color is just an accident.
Greg Rouse giving his Interview at Scripps Institution of Oceanography in La Jolla, USAImage: Rainer Dückerhoff
Are all of the animals living down there blind?
Yes, most of them are. Some of the shrimps that live in the mid-Atlantic ridge have eyes, but the functionality of these eyes isn't very well known. The shrimps that live near the hot water are actually able to detect infrared light from the hot water. So they know not to go near it. The scale worms we found have no eyes, they must sense each other from the movement of the water. But even if something has eyes, we don't know if the animals can see with them. We can ask a lot of questions but for many of these animals we don't have any answers.
How do the animals move from one vent to another? Because at one point, a vent will eventually die, right?
They have a lot of larvae — babies that is — floating in the plankton. These can be in the plankton for months. Most of them will die but some of them will find the next vent.
This scale worm is one of the many fascinating organisms, living at the Pescadero Basin. Image: Rainer Dückerhoff
At a depth of 4,000 meters, the pressure is more than 400 times the pressure that we are used to. How can an animal live under this enormous pressure?
There are animals that really do live well under pressure and they're adapted to that and if you take them out of that pressure they will die quickly. There are also bacteria that can only exist under very high pressure. But for instance, there are no fish that live below 8,000 meters or 26,250 feet.
There appear to be pressure limits at which animal physiology is fundamentally disrupted. We think it might be due to pressure effects on proteins and other things that we don't really understand very well. If you take the pressure off the proteins, they change their structure. If you apply more pressure to proteins and other chemicals, then the physiology will also break down for the animals.
You brought animals back from Pescadero Basin. How do you manage to bring them up from that depth?
We immediately kept them cold. So we put them back into very cold 2 or 3 degree Celsius, and some of them will survive for a few hours. Xenoturbellas for example, they relaxed and they were crawling around. But we always find by the next day usually things from that depth are dead. If things come from 1,000 meters or shallower, it's normally okay, we can keep them alive, even here in the lab for as long as we keep them cold. But anything below 1,000 meters you'd need normally have to keep them under pressure to keep them alive for anything more than a day.
Greg Rouse is a marine biologist at Scripps Institution of Oceanography in La Jolla, USA. He went on the ‘Falkor' cruise to Pescadero Basin in November 2018. The freezer in his lab holds reams of still unknown species, many of which live at hydrothermal vents in the deep sea.
Brigitte Osterath conducted the interview.
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Image: University of Southampton
Hairy-chested "Hoff" crab
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Image: David Shale
Undersea snail
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Image: David Shale
Ragworm
A species of ragworm, Hesiolyra cf. bergi, found at the Longqi vent field also lives at hydrothermal vents more than 10,000km away at hydrothermal vents in the eastern Pacific.
Image: David Shale
Scaleworm
A new species of scaleworm Peinaleopolynoe n. sp. discovered in an area licensed for undersea mining.
Image: David Shale
Mussel and scaleworm
The mussel Bathymodiolus marisindicus collected from Longqi. A commensal scaleworm Branchipolynoe sp. is also visible inside the mussel.
Image: David Shale
Sea cucumber
A holothurian (or sea cucumber) Chiridota sp. collected from Longqi. In some Asian countries sea cucumbers are considered a delicacy.
Image: David Shale
Barnacle
A stalked barnacle Neolepas sp. collected from Longqi.
