Oceans are massive bodies of salt water that cover the majority of Earth's surface, and ocean biomes have some special terminology we should go over. Now the Littoral zone of oceans is a little different. You see, the water line where oceans meet the land is not fixed. Oceans have a tide, so the water level will actually flow from the high tide point to the low tide point, and this area, this littoral zone is called the intertidal zone. And here, we're looking at it, you know, as a beachhead, but sometimes these intertidal zones will actually be rocky and can have verticality to them, and they can also have depressions that water gets trapped in that we call tide pools. And tide pools can be incredibly rich and diverse ecosystems.

Now the area that extends out from the littoral zone or the intertidal zone is called the neritic zone, and this is basically just shallow ocean that covers the continental shelf. Now the continental shelf is the extension of land that comes off of continents, that goes underwater. So, you know, imagine, if you were to pull the continent out of the ocean a little bit, you know, this would just look like a continuation of the land mass. Now at the edge of the continental shelf, you'll have a sharp drop off, and there is where you get open ocean. Scary stuff. The open ocean or the zone, of open ocean is called the oceanic pelagic zone, and it's just what's beyond the continental shelf.

Now the benthic zone in oceans is going to be, you know, markedly different from the benthic zone of a lake, for example, because oceans are so much deeper and more vast. Now, the marine benthic zone as it's called, or sea floor if you prefer, is basically in darkness always. Now coastal areas will receive light if the benthic zone is shallow enough. However, the majority of the marine benthic zone is going to be in total darkness.

Now coral reefs are, you know, it's hard to oversell them. They're just incredible ecosystems, and, you know, they're such a rich biome in terms of species and in terms of, you know, the sort of services they provide to the areas around them. And here's a map, you can see the location of coral reefs all over the world. They're going to be built by coral, which are these little animals that secrete these structures made of calcium carbonate. It's probably what you picture when you think of coral. And those calcium carbonate structures are, you know, probably look at them and think of them as rock or something. It's actually not rock, but, you know, you can see these structures here in this, this mass of coral.

Now the reason I bring up calcium carbonate is because coral reefs are super threatened by ocean acidification. Calcium carbonate will readily react with acids because carbonate is a base. So even a small increase in acidity can result in great damage to coral reefs, and you can see it from satellite photos, you know, looking at the Great Barrier Reef, see just how much of that has been eroded.

The last biome I want to talk about are these deep sea hydrothermal vents. These are fissures in the Earth that release geothermally heated water, really, really, hot water. And there are two reasons I want to bring these up. One is because they're potentially the source of life on Earth. Here, you can see what's called the lost city. These are a special group of hydrothermal vents that form these carbon stacks, and it has been proposed that life may have started in the little nanotubes in these carbon stacks. I'm not going to get too much into the details, but, you know, it's cool stuff. It's a very interesting theory whether or not you believe it.

Now, this is the other reason I wanted to bring up these hydrothermal vents because they have some really interesting ecosystems, or rather say communities of organisms that have developed, there. You see, pretty much everywhere we've been talking about up to this point, has been a community that's more or less supported on photosynthetic organisms. But these communities are not supported by photoautotrophs, but by chemoautotrophs. They're supported by bacteria and archaea that can, you know, essentially fix carbon from the, you know, from performing various chemical reactions with the inorganic, compounds available to them from these hydrothermal vents. Basically, they're just very cool ecosystems because they're so different from, like, everything else we see. You know, it's, they're super unique in that there's, like, a very rich diverse community built on top entirely on top of chemoautotrophs. You know, we're so deep down, there's no photosynthesis happening here. So very cool stuff. Now that's all I have for this lesson, I'll see you guys next time.