You wanted to know: what are these phytoplankton?
By Rose Eveleth | June 8, 2012 |
First, thanks to everyone for asking such fabulous questions. I’m going to try to get to them all, but you’re an inquisitive bunch so I might have to miss a few. I’ve also found that they group into a couple of different general topics – so I’ll try to do them in clusters…like this post!
Many of you have asked about the weird phytoplankton that the scientists are studying.
First, generally, what’s a plankton? The name comes from the greek word “planktos” which means “wandering” or “drifting.” Which makes sense considering plankton float through the oceans. A phytoplankton is a plant plankton – meaning it makes its own food from the sun. (There are also zooplankton, which are animals like krill and jellyfish.) In the world’s oceans, there are about 5000 species of phytoplankton. You can’t see them when you look at the water, but hidden in just a cup of seawater can be thousands of little plants, each with their own unique structure and life.
Why do phytoplanktons look like jewels? Do their unique structures indicate something about their functions? Jayinee Basu, from California
It’s true, plankton are beautiful. Just look at them!
Their structures do indeed correspond to what they have to do in the ocean (just like our bodies help us move around in our world). Let’s look at the plankton we’re studying in particular – named Emiliania huxleyi (commonly abbreviated to Ehux. Check out how pretty it is.
These little phytoplankton are coccolithophores – a group of phytoplanknton distinguished by those exterior plates you can see in the images. Ehux evolved about 270,000 years ago, and is now one of the most common coccolithophore species on earth (which is good for our research boat, since we’re looking for them). You can find Ehux all over the planet, from Portugal to the Philippines. The only place you can’t find Ehux is at the frozen poles, where it’s just too cold.
Those plates – the things that make it a coccolithophore – are called coccoliths (makes sense, right?). They’re made of calcium carbonate, and each little plate is between 2 and 25 micrometers across. That’s about a quarter the width of a human hair.
These coccoliths are quite elaborate, and the process the plankton goes through to create them is complex. But, weirdly enough, scientists aren’t totally sure why they have them. It’s possible that the little shells protect them against being eaten by bigger, hungry zooplankton. Or maybe it protects them from infection by bacteria and viruses (we’ll talk about viruses in a later post). Maybe the coccoliths help them float, or photosynthesize, or keep out harmful UV light. We really don’t know.
Each individual Ehux is super tiny – about 5 micrometers wide – slightly smaller than a human red blood cell. But I mentioned earlier that we can actually see them from space. Some of you were wondering how that’s possible.
How come they can see this phytoplankton from a satellite? Brenda Wright from Salt Lake City, Utah
How are satellite data used to track the plankton? Antonio Mario from Brazil
Of course, even with advanced satellites, we can’t see an individual phytoplankton from space. But when there are loads of them all gathered together, satellites can see them. It’s kind of funny, because like I mentioned before, you might scoop up a whole cup of seawater and not see a single phytoplankton without a microscope.
Satellites can see them, however, because coccolithophore shells are made from calcite, and calcite reflects light. So light from the sun bounces off those calcite shells, and creates patches of white that the satellites see in big pictures like this one.
Okay, so they’re tiny, they’re pretty, and we can see them from space. But, some of you asked, why do we care?
What makes these coccolithophores so important? Are they important for scientists studying climate change or are they important in the food chain, or both, or something completely different? Rona from New Jersey
Why are phytoplankton of so much interest? What effect do they have on marine life? Je Dei Sawse Queens from New York
These phytoplankton are important for a whole bunch of reasons. First, they provide food for the ocean. Phytoplankton get eaten by zooplankton, who then get eaten by fish and whales, and so on up the food chain. Think of phytoplankton like the grass and trees that feed herbivores on land, who then get eaten by bigger predators.
But these plankton aren’t just important as food – they’re also important for our atmosphere. When you think of what produces oxygen, you probably think of trees. But phytoplankton are responsible for half of the photosynthesis that happens on earth, and thus about half the oxygen in our atmosphere. We can thank phytoplankton for every other breath we take.
It’s not just what the plankton produce that’s important — it’s also what they consume. Every year there are 45 billion tons of new phytoplankton (and for Jim Wallstrum from Washington, who asked how Ehux reproduces, they can reproduce both sexually and asexually, and have a haploid and diploid stage). But at any given moment, there’s less than one billion tons of phytoplankton in the ocean. So where do they all go? Turns out the phytoplankton don’t live very long, and when they die, they sink down into the ocean. As they sink, they take all sorts of minerals and carbon dioxide with them. Down in the deep cold waters of the ocean there’s layer upon layer of dead phytoplankton. Some of those bodies, about 0.1% of them, get buried in the sediment and, eventually turned into oil – the same kind we use to drive our cars. The rest of the dead phytoplankton decay slowly, get used by other organisms, or stay in the water.
Those nutrients don’t stay buried forever though. In fact, there’s a very important and very slow pump that eventually brings them to the surface and returns the gases to the atmosphere and the nutrients to ocean life. This balance between sinking phytoplankton and re-emerging gases is important for maintaining not only life in the ocean, but the stability of our atmosphere.
The plankton have lots of other important functions, but we’ll talk about just one more: albedo. Albedo is the reflectiveness of the surface of the earth. Snow is more reflective than thick forests – far more light from the sun bounces back off the snow than it does off forests. When the phytoplankton bloom, they reflect a lot of the sun (remember we can see those reflections with satellites) and thus increase the albedo of the earth. Some of that light gets reabsorbed by the atmosphere and heats it up, while some of it escapes back into space. Albedo is on of the important factors that determines just how hot our atmosphere is.
So that’s what these phytoplankton are, what they do, and what they look like.