Growing Copepods

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Editor's note: The LTER zooplankton team has generously allowed Karen some time and resources to do some of her own work.

While here in Antarctica, I am trying to grow copepods.  Copepods are small crustaceans that are part of the zooplankton, a word for all animals whose movement in the sea is mainly due to the movement of their liquid surroundings.  Their sizes range from less than one millimeter to several.  They have complex life histories, involving both naupliar and copepodite stages, before reaching maturity.  Copepod growth rates are thought to be primarily controlled by food availability, while their development rates are likely linked more to temperature.  Therefore, under different temperature conditions, it is likely that copepods will mature at different sizes.  I would like to find out what the relationship is between copepod egg development and temperature; eggs are interesting in this respect because they do not require food from the environment outside of the egg.  

I began by collecting live copepods in a net, selecting out mature females, carefully placing them in glass petri dishes.  I placed trays of petri dishes into two incubators at two different temperatures (0 and approximately 4 degrees Celsius).  The first time I did this, the copepods lived for about four days and that was it; nothing happened.  I was a little discouraged.
1_Assorted copepods.jpg
Many copepods together under a microscope; there are a few different species here.  The red-colored bits are their antennae, which they use to sense their surroundings.

petri_dishes_comp.JPG
A tray of petri dishes sitting at the bottom of the 0 degree incubator. I had to keep them at the bottom of the incubator, or they would freeze: a lesson learned by mishap.

The second time I tried the experiment, I had better luck.  The copepods I selected laid eggs within a couple days in the warmer incubator and within a couple more days in the colder one!  The eggs have yet to hatch and may have stopped developing.  The copepods that laid eggs were a Calanus species, the ones with the red antennae, which I have yet to identify to a species level.  

Calanus_expt_comp.JPG
Calanus sp. used in my experiment
Editor's note: Notice the shiny sack of  oil filling out the copepod's carapace.  This is why everyone wants to eat Calanus.  

eggs_comp.JPG
Copepod eggs

There is incredible copepod diversity here; it is both exciting and a little overwhelming trying to learn the different species.
2_Candacia spp.jpg
A copepod of the genus Candacia, distinguishable by its frilly black legs.  When Candacia are floating around in a tub with lots of other zooplankton, all you can see is their legs because their bodies are transparent.
Editor's note: I think Candacia would be an excellent candidate for the next stuffed copepod.
3_Paraeuchaeta antarctica.jpg
A mature female Paraeuchaeta antarctica, with a spermatophore attached to her uromsome (tail).
Editor's note: Paraeuchaeta is a voracious predator.  Not quite in the same league as a honey badger, but close.
Paraeuchaeta antarctica seta on Pr5_comp.JPG
The setae on the posterial corners of a Paraeuchaeta antarctica: a feature that helps distinguish this copepod from other species.

I am still working on definitively identifying the Calanus species that I used in my experiment; they may be Calanus propinquus.  You can tell the difference between Calanus spp. and Calanoides spp. by a serrated upper, inner edge of the most rear swimming legs.  Try seeing that in a microscope on a moving ship!  It's a great challenge.

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This page contains a single entry by Andy Pershing published on February 4, 2012 10:00 AM.

A More Detailed Look at Zooplankton--Salps & Their Poop was the previous entry in this blog.

Sea Ice is the next entry in this blog.

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