As I mentioned in the last post, we spend a lot of time looking at zooplankton trough microscopes. We have 3 main tasks that require scopes 1) Distinguishing hard to identify species 2) cataloging the tiniest species we get in the net and 3) determining the sex and stage (readiness for breeding) of krill. I just learned how to sex and stage krill this year. It is a combination of fun and frustration. All of their little bits are tiny tiny tiny and transparent, so only a few of the microscopes we have are good enough for the job. Sadly the camera does not play well with those scopes, so I can’t show you all about krill bits. I can, however show you the cool tiny creatures we look at.
You can tell that I am working in the Antarctic because there is a penguin sticker on the scope . That scope is my favorite scope. It is also the oldest scope in the lab, but it has the best lenses and light source. The krill bits just jump right out on that scope, usually. All photos below come from the lab camera scope. Most were taken by Javier Arata as he has the magic touch with that setup.
We get a lot euphausids in the net. When they are big, we can easily determine the species. But when they are small or missing their eyes we often need to use the microscope to look at their rostrums to determine the species.
Our first contestant Is Euphausia frigida. As an adult frigida tends to be quite small, lacking in color, and it has round eyes that sometimes go missing or get squashed. When you look at frigida under the scope, you can see that its rostrum tends to be blunt, and doesn’t have a crease in the middle.
In contrast. Thysanoessa macrura (T. mac) has kidney bean shaped eyes, and a pointy rostrum with an obvious crease down the middle. Both T. mac and frigida tend to be small and colorless so we spend a lot of time scoping these guys out.
Pretty cool right? Once you get used to looking for the signs, its really easy to tell the species apart.
We are also really interested “baby krill” or more accurately , the larval stages of Euphausia superba known as furcilia. You can tell how old they are by counting the spines at the tip of their tales. I am not kidding, we count microscopic spines on tails.
Ok let’s zoom in on those tail spines.
As the furcilia grows it will loose spines. An F V stage has 3 spines, and the oldest furcilia stage (F VI) has only 1 spine. Counting spines is a lot of zooming in and zooming out, but its pretty easy once you get the hang of it.
Ok enough euphausids, lets talk about copepods. Copepods are awesome. They are tiny little armored beasts that feed and evade predators by doing this cool spiral dance. There is a tremendous amount of copepod diversity down here We can recognize a handful of species that are pretty distinct, but a lot of times we can only determine the family or that it is a copepod. Let me show you.
Candacia is great! It looks furry or feathered. it stands out amongst all other copepods. Even though we don’t get many of them, they are hard to miss, and hard to misidentify.
This mighty beast is Calanus propinquus. We identify it by its size, color, and shape. It is quite large for a copepod. We can actually see it as an orange speck darting around the sample. Its shape is characteristic of the Calanid family of copepods. So if it is not fully grown and pigmented, we can’t tell if it is actually C. propinquus or some other calanid copepod.
So the copepod above is smaller than propinquus, lacks color on the tail and antennae, but has the same body shape. They look very similar, but not quite the same. We are confident that they are both in the same family, Calanidae, but that is as far as we can get. One day we had to use forseps (aka science tweezers) to hand pick 504 calanid copepods for a diet study. The little buggers are fast and tiny, so that was no easy feat..
Now to completely blow your mind, we also get super tiny crustaceans. The critter in the bottom of the picture, is a fully grown Scina sp, and it is smaller than a Calanid copepod. They are pretty weird looking, but always so much fun to find.
We get an assortment of fun tiny amphipods as well.
Eusirus propedentatus is one of my favorites. Every critter in the Eusirus genus has little boxing glove claws, but in this part of Antarctica the only one with red gloves is E. properdentatus.
We get little Primno macropas in almost every tow. When they get larger, they are quite purple. They almost look like a purple outline of themselves in the big sample dish.
We also get gastropds in our samples. We get these beautiful little shelless snails, that you might know as pteropods . The two most common species and the only ones we can positively identify are below.
Let’s not forget the super fun looking polychaete worms we get.
And with that friends, I think you are ready to join me at the microscope to “small frac”. Small frac is when we take all of the water associated with the sample, and strain it to isolate these tiny critters. Then we mix all of the solid bits left behind with a specific and known amount of clean seawater. We take sub-samples of this mixture and count every single critter we find in it. We use gridded petri dishes to help us keep track of what has already been counted. We can then extrapolate (multiply) to how many of each kind of critter is in the full sample.
Do you recognize anything in the grid cell above? There should b e a few critters you have seen before.
Hope you liked seeing the tiny, tiny critters.