Thanks to Skillshare for supporting this episode of Journey to the Microcosmos.

The first 1,000 people to click the link in the description can get a free trial of Skillshare’s Premium Membership. Learning about ecology can make the world look like one big buffet, except all the dishes are each other.

At the start, you have the photosynthetic organisms churning sunlight into sugar, and everything just cascades into culinary chaos from there. There’s ciliates eating algae, ciliates eating other ciliates, rotifers and fish and everything else that comes after. And somewhere, reigning comfortable from its spot in the middle of it all is this, the copepod.

At first glance, the copepod probably doesn’t seem any more significant than any other animal. I mean, it looks a little strange, but crustaceans usually do. There are more than 20,000 species of copepods in the world, and these various species have managed to find their way into just about every type of water, no matter the temperature or the salinity.

There are species in freshwater ponds, species in oceans, and species deep in hydrothermal vents. And just as they’ve managed to find so many different /places/ to live, so have they found many different /ways/ to live. Some swim freely through those waters, others pursue a more parasitic strategy.

And some become hosts for parasites themselves, like the Guinea worm, which enters the copepod as a larva, and leaves ready to infect whoever has eaten the copepod. But however many different types of copepods are out there in the world, they do have a few things in common. They hatch from eggs, beginning their lives as a round, not fully formed version of itself.

The copepod molts several times from this larval stage, its body lengthening and forming more pronounced divisions as it goes through a youthful “copepodite” stage. And eventually, the copepod reaches its adult form, its segmented body forming a tapered shape encased in an armored exoskeleton. Copepods have a very simple eye that senses light, which they use to orient themselves in water.

A few species are even capable of something like vision. But perhaps the copepod’s most essential sensing comes from its two pairs of antennae—the most noticeable of which is that almost comically large set that you see here. And along the length of those antennae are small, sensory hairs called setae that help the copepod detect changes in its surroundings.

Now, those antennae don’t just sense, they also help the copepod mate. When a male copepod finds a female copepod who he likes very, very much, he can bend the antennae to grab her. And that might sound like a funny detail about an equally funny-looking part of a copepod’s body, but it’s also part of its success.

When you’re a tiny animal trying to reproduce in a big body of water, the vastness of your surroundings makes it enormously difficult to find a mate. It would be like trying to find a date on Tinder, except like 99% of the profiles you’re swiping through are just pictures of water. So when you find someone, you really have to hold on to them.

Copepods of course aren’t the only animals facing this challenge. There are lots of animals in the ocean that are just too tiny to overcome the ocean’s currents and the way that water feels like honey when you’re that size. As a collective, they’re called zooplankton, and they spend their life drifting where the currents take them in the hopes that food will also be there.

The zooplankton’s diet makes them a valuable part of the ecology buffet because they’re at that spot right next to the organisms who start the whole thing out, munching away at the diatoms and other photosynthesizers of the water. In the case of copepods, scientists observed individuals of one species eating around 11,000-373,000 diatoms every day! And as beautiful as diatoms are, and as much as we like to look at them, the world would be very different if there was no one trying to eat hundreds of thousands of them a day.

It would be a buffet with diatoms spilling out of the trays, leaving no room for anything else. But copepods and their fellow zooplankton fill that essential ecological role, acting like a middle man that connects diatoms to the rest of us. And somehow, over the millions of years that copepods have been around, they have become the preeminent zooplankton--a kind of king amongst middlemen, dominating zooplankton populations in many bodies of water all over the world, including Antarctic lakes.

In Lake Baikal in Russia, the deepest freshwater lake in the world, copepods are estimated to make up 96% of the zooplankton population. And out in the oceans, copepods reign supreme. So, the question is how?

And the answer is probably much more complex than any one single trait, especially if we attempt side-by-side comparisons with every single animal that makes up the zooplankton of every single body of water. But if we consider the ocean—the vast, vast ocean, where food and mates both are difficult to come by—the copepod has a number of talents that do help it survive. It is, for one, very sensitive to its surroundings.

Those hairs in its antenna detect predators and prey alike through changes in the water velocity around it. If the copepod detects a predator, it can quickly jump away, using 4 or 5 pairs of legs to jump up to 1000 body lengths per second, making the copepod much faster than other animals of its size. And if the copepod detects prey, it can launch itself into a quick ambush instead.

So speed is one advantage that may help the copepod survive. But this organism doesn’t rely on ambushing alone to sustain itself. It’s also capable of a much more sustained search for food by vibrating some of its appendages, which creates a feeding current that the copepod can scan and dine upon like its own personal banquet.

And these are seemingly small talents that stack up, producing in its totality an animal that is capable of feeding, escaping, and mating its way to success in the vast open ocean. And with each diatom the copepod eats, their strange regime becomes only more influential because one day a fish will probably eat that copepod, and eventually another animal, maybe even you, will eat that fish--connecting us all to a strange little crustacean in the sea whose kingdom has no boundary. Thank you for coming on this journey with us as we explore the unseen world that surrounds us.

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If you’re one of the first 1,000 people to click on the link in the description, you can get a free trial of Skillshare’s Premium Membership. The folks you’re seeing on the screen right now. They are a bunch of people who have definitely like absorbed some of the nutrition that once was contained inside of a copepod, but that is also true of all humans.

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