Sunday, November 16, 2014

Suspiciously Helpful Drifters

I can't contain it any longer! The blog has been active for three months now and we've barely talked about the most amazing, most important, most spectacular group of living things on the planet! Well no more. Prepare yourselves to meet the very reason for life on earth as we know it...

Oh look it's even waving hello
Courtesy Lindsay Waldrop via Flickr

Well not that specifically, that's just a baby barnacle, we'll come back to him/her (I'm not being politically correct, barnacles are hermaphrodites) in little bit. What I'm talking about is plankton. And I'm not exaggerating when I say that plankton are why we have the planet that we do. They've shaped evolution since the beginning of life, and they continue to do so today. So this week we're going to take some time to learn about our magnificent, mostly tiny, benefactors.

The word plankton itself has a pretty cool story. It comes from the same Greek word as planet, Planktos, which means wandering. Planets seen from earth look like stars and they do this weird thing where they kind of meander across the sky. Because of this, the ancient Greeks called them "wandering stars" in their own language. A couple thousand years later a German physiologist named Victor Hensen saw all these living things wandering on currents around the Baltic sea and gave them the name.

Another important part of plankton is the fact that it's not a term to describe how things are related to each other genetically. Saying something is plankton isn't like saying something is a mammal; it's more like saying it's a carnivore. The word describes behavior not biology. That's how algae (referred to as phytoplankton) and animals (called zooplankton) can both be plankton. Any living thing that is moved around by currents, tides, and waves more than it can move itself is plankton.

Pictured: Plankton
Courtesy Ian Sanderson via Flickr

That's right any living thing, so even giant jellyfish are technically plankton. Naturally being very small makes it a lot harder to resist the movement of water so the vast majority of plankton are pretty tiny. Sometimes this means that zooplankton are baby versions of the familiar species we find on the beach.

Take that baby barnacle that we met at the beginning for instance. He/she is a perfect example of meroplankton (they're plankton for merely part of their life). Gravid (the egg-laying version of pregnant) barnacles launch out those tiny babies when they hatch. The babies are then free to spend the next couple weeks cruising the currents eating and growing strong; before settling down to stay in one spot for the rest of their life. These baby, or larval forms as they're known, are actually really important for scientists trying figure out how animals are related to one another. We thought barnacles were related to snails until the mid-1800's when we had good enough microscopes to see that the larvae are more like shrimp.

Of course just because something is small doesn't mean it's a baby. Many living things are plankton permanently. These are called holoplankton (they're plankton for their whole life) and they are incredibly important to the ocean's food web. The two classic examples of this are copepods (pronounced cope-uh-pods) and krill. Both are crustaceans, just like the barnacle, and between the two of them they directly or indirectly feed almost everything in the ocean.

 A copepod (on the left) and a krill (on the right), you've probably seen them in TV and Movies
Courtesy NOAA Great Lakes and Norkrill via Flickr

What these two groups of animals lack in size, they make up for in numbers. Around Antarctica alone it's estimated there are around 500 million tons of just krill! One krill weighs about seven tenths of an ounce. There are literally uncountable numbers of these animals in the ocean. There are so many that we get into numbers that human brains actually have a hard time comprehending. You start to understand how something as massive as baleen whales can live off these two animal groups almost exclusively.

So zooplankton are clearly important to the health of the oceans, but what about the algae, those phytoplankton from before? Well we wouldn't have things like krill and copepods without those phytoplankton, and in fact we probably wouldn't have ourselves either. Like plants on land phytoplankton are at the bottom of almost every ocean food chain. They take sunlight and carbon dioxide and turn it into sugar, which things like krill and copepods love to eat. So the copepods gobble up the phytoplankton, and then they're gobbled up by fish, and on and on, all the way up to you. When you eat a fish you're eating everything that fish ate, plus everything that fish's prey ate, plus everything that fish's, prey's, prey ate. It starts to look pretty important to keep the plankton's tiny ecosystem healthy doesn't it?

Not only do phytoplankton make life work because they're food for other living things, but they provide complex life with something extremely important. Go ahead and take two really deep breaths for me. Nice, long, slow, relaxing breaths from your diaphragm. Feels good doesn't it? All that fresh oxygen to your brain and muscles really does you good. Well amazingly the oxygen in one of those breaths came from phytoplankton.

"You're welcome!"
Courtesy NOAA Photo Library via Flickr

It's been calculated that about half of the oxygen in the earth's atmosphere comes from the ocean. That means that phytoplankton are at least as important as all the terrestrial forests, all the savannahs, and all the shrub lands, combined. Remember how I mentioned that we can't even count the number of krill or copepods? Well to make that many animals you need even more of these algae. There are so many phytoplankton in the ocean that they actually dye huge swathes of the ocean green during the summer, which can be seen from space! Not only does phytoplankton sustain us complex organisms, it's partly responsible for us being here in the first place. 

On the very ancient earth most of the oxygen in the atmosphere was tied in with other gasses, like carbon dioxide, and what was escaping, quickly came out of the air to rust the metals in rocks. But then a group of photosynthesizing bacteria evolved multi-cellularity. All of a sudden there were way more organisms using up the CO2 and dumping out a lot more oxygen than the rocks could absorb, and BAM! They created an atmosphere full of an element that's essential for biological processes in animals.

So that's it for this week. I could write even more about plankton: how they have the single largest migration on earth, how they provide food for the deep ocean with their poop, and I will eventually; but for now let's just appreciate the incredible, essential plankton by looking at this wonderful picture of a spring bloom in the Atlantic.

For scale: that's Ireland at the top middle. This is a real color photo
Courtesy NASA Goddard Space Flight via Flickr


Carefoot, Tom, "Learn About Acorn Barnacles", A Snail's Odyssey

Sessions et al. "The Continuing Puzzle of the Great Oxidation Event" Current Biology 19, 2009, DOI 10.1016/j.cub.2009.05.054, Accessed via:

Shirrmeister, et al., "Evolution of multicellularity coninsided with increased diversification of cyanobacteria and the Great Oxidation Event." Proceedings of the Natural Academy of Sciences, vol. 110 no. 5, pg. 1791-1796, DOI 10.1073/PNAS.120992710 Accessed via:

Krill Facts Center, International Health and Science Foundation

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