Limpets….Going where squirrels fear to tread!

 

Ok, so when we left off yesterday, I had introduced you to some Limpets, and we had looked a bit at how they are not as static as they seem.

Today we are going where squirrels fear to tread, to some truly bizarre habitats.  I hope I can show you some new places which you did not know about, and if you knew about them, then I hope I can show you something interesting  anyway.

Our Limpet friend for the day is Neolepedtopsidae (don’t worry, I can’t pronounce it either, so I will go with “neoleppytopsy” or Topsy for short).  This is a newishly described family of limpets, first described in 1990, and the name means “New lepedtopsidae”, which does not make it any clearer, but, the Lepedtopsidae are an extinct group of limpets, so this is a family which has evolved from the ancient group.

I said yesterday that limpets are found on beaches, which makes it a little strange that we discovered this family only in 1990, as, most beaches are fairly well explored.

This is an image of a species called Eulepetopsis vitrea, which are part of the family of Neolepedtopsidae.

Eulepetopsis vitrea, image from EOL (Encylopedia of Life)

So, where was this lovely little animal hiding?  Let me show you what these animals consider an upmarket address:

The East Pacific Rise, home to our lovely little limpet. Image from Wikipedia

As that is a little zoomed out (Sort of a neighbourhood shot), lets zoom in a little, and see an image from one of my favourite institutions (I used to really want to work there, but I have a thing for water after a bumpy ferry journey in the UK, so not so into that now), the Woods Hole Oceanographic Institute:

Black Smoker on the East Pacific Rise. Image from Woods Hole Institute

Yes, that is a robotic arm that you see in the photo, but it is not because Terminator has happened and the robots are now running the world, it is because these are at a depth of  anything up to 2-3km underwater.  Not quite as deep as the mid-ocean trenches (These reach 10km in the deepest parts!), but still a bit beyond dive range!

I have cunningly managed to fit two of my favourite subjects, geology and ecology into this post, so here comes the sneaky geology part:

The East Pacific Rise runs from just north of Antarctica to California, and is the line running up the right hand side of the ocean floor on this image:

East Pacific Rise, image from Wikipedia

This is what the shape of the “land” looks like at the East Pacific Rise (This is called a bathymetric image, if it was above ground, it would be a topographical map, those circles you see drawn onto maps show height, and this does the same thing, only underwater…It is called bathymetry instead of topometry because it is underwater, and means “deep measures” in greek)

Bathymetric image of the East Pacific Rise, image from NOAA

The reds indicate the highest parts of the ridge, and as it goes through yellow, to green to blue, it gets deeper.  I am a bit fanatical about these undersea areas, because a) they are very very cool, and b) they have amazing features and creatures that we have only just begun to discover.

So, what on earth is this Pacific Rise, and what is it doing messing up the nice smooth ocean bottom?  Well….until the late 19th century, we had no idea what the ocean floor looked like, and many people thought it was flat and featureless, and probably not very deep.  Then an expedition was sent out to map the ocean floor by the Royal Navy, and they did this by chucking lengths of rope with distance markers over the side of the ship (this is known as sounding, which refers to any technique for measuring depth).  Luckily, they took a lot of rope with them, because, as they were going across the Atlantic, they hit a spot where the rope just kept going and going.  It finally hit the bottom at just over 8km deep, in an area known as the “Challenger Deep” (You might have heard of this from when James Cameron did his dive there earlier this year).

After the second world war, there was an increase in ocean mapping (Well, they had to put all those ships and sonar to good use), and as the data was compiled from these expeditions, it became clear that there were a series of lines running round the oceans, and that there were ridges as well as deep valleys.  This is one of the things which helped prove tectonic plate theory, and caused a lot of discussion at the time, about whether the results from sonar had been interpreted correctly, as obviously there was not a complete map of the ocean floor, so maybe they had filled bits in wrong.

The reason the discovery of these ridges helped prove plate tectonics is because, whilst it had been suggested that the continents had been closer together, and even joined into a super continent,and there was geological evidence for this, rocks from different continents matching together, but there did not seem to be a mechanism which could explain what the ocean was doing in the middle of the continents now.

The ridges are where new crust is formed, magma rises up from below the crust, and at the mid ocean ridges spills out, creating new ocean crust.  This is then carried across the oceans, until it reaches the edges of the continental plates, where subduction occurs, and it is pulled back down below the crust as the ocean plate goes under the continental plates.  This is also the reason why the ocean floor is so young compared to other rocks on the surface, with the oldest parts of the ocean floor (near the subduction zones) being a little under 200 million years old.  In contrast, some of the oldest continental rocks are 3.8 billion years old.  So, the big red ridge on the image is where new ocean floor is formed, and as the new material is continuously ejected from below the mantle, it pushes the other material away from the ridge, in the East Pacific Rise, this happens at a rate of 6-16cm per year.

The black smokers, which our limpets live on and around, are formed when sea water (Which is very cold at those depths), gets into the cracks in the ridge.  This means that very cold water under pressure  meets very hot molten rock.  The water becomes superheated, it cannot turn to gas because of the pressures at those depths, so it is liquid water at 400 degrees.  At this temperature, it is less dense than the surrounding water, and so shoots up in a column.  The reason that it is not clear water is because it has dissolved minerals in it from inside the crust, and is very rich in sulfur compounds.

This sounds like very hostile conditions for life….no sunlight, very hot water spewing out of cracks, lots of sulfur, and very high pressure (25 atmospheres at 2500m deep, at sea level, the pressure is 1 atmosphere), but, surprisingly, our very few expeditions to these locations has uncovered an amazing array of organisms thriving!

Instead of phototrophs like we have at the surface, the primary producers (equivalent of trees) are chemotrophs, which make their food from the sulfur and other chemicals emitted by the vents, and a whole food web, right up to fairly large predators, there has even been an octopus sighted near one of these vents!

These vents are of great interest to science, and a branch of biology called Astrobiology, which is concerned with the possibility of life on other planets, is interested in these vents as they illustrate how life can survive in an environment without oxygen and sunlight, and in acidic, sulfur rich conditions. (Astrobiology is also called Exobiology).

For me, these vents are one of the reasons I feel that we need to investigate our planet before venturing into space.  According to NOAA, we have covered less than 0.1% of the ocean ridges with our submersible expeditions (They tend to return to the same locations), and overall, we have explored less than 5% of the deep ocean, and the bits we have explored have revealed some amazing creatures, so what else is hiding down there, waiting for us to investigate?  The bottom trawling which occurs in much of the worlds oceans tends to flatten the bottom of the ocean where the trawlers fish, and damages seamounts, which are underwater mountains, home to many communities as yet undiscovered by humans, yet being damaged by deep sea trawling.

We only discovered these vents in the 1970s, and have barely begun investigating the deep ocean, so I look forward to many more exciting discoveries in the future.

Finally, here are some images of the communities which exist by these vents…the density of organisms is astounding!

Crabs and mussels on a deep sea vent, image from marinebio.net

An Octopus living near an Antarctic Hydrothermal vent. Image from Scientific American

Finally, here is a video showing a “Yeti crab”(Kiwa hirsuta) colony, again, near Antarctica.


I hope I have shown you some interesting things today, and that you did not fall asleep in my wall of text!

 

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4 thoughts on “Limpets….Going where squirrels fear to tread!

  1. Hot stuff! I enjoyed this post but I’m going to lock my bathroom door more carefully in future. Bathymetrists chucking lengths of rope into the tub will have to wait until I’m up and dressed.

    You have a good point about exploring deep oceans before we charge off into deep space. Also about keeping the deep-sea trawlers in check.

  2. Pingback: Friday Documentary | Skeptical Squirrel

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