Caprellid fight club: spines vs poison tooth

The first rule of fight club is that you don’t talk about fight club. I set up a competition for space between two species of caprellids, and I’m going to break the first rule and tell you all of the epic details. Caprella mutica is an invasive species whose back is covered in spines, and Caprella laeviuscula is a native species that has a poison tooth it uses to kill enemies. This sounds like a pretty epic fight, and I’m sure you’re all dying to see some action photos.


Can you see them fighting? I think one just used a right hook! Photo: Emily Lim

These organisms are only about 15 mm long, and I need to use a microscope to identify them, but that doesn’t make their battles for space any less cool.


C. mutica. Photo:


C. laeviuscula. Photo: http://www.dfo/








If you go out to a dock in Vancouver and lean over the side, you’re most likely to find the native C. laeviuscula and the invasive C. mutica clinging to the Obelia growing on the dock. I started getting really interested in caprellids, so I thought it would be a fun project to investigate competition for space between these two species!


I also decided that Obelia makes a great beard. Scientists are weird, ok? Don’t judge me. Photo: Chris Harley

Now I know what you’re thinking. Why does anyone care? Beyond my own personal interest, I think caprellids will make really good model organisms. Model organisms are organisms that we might not care about much, but they’re useful for testing theories on. One of the most famous model organisms is the fruit fly. No one really cares about fruit flies, but scientists have used them to test many hypotheses, especially in genetics. I think that caprellids would be a fun species to use to answer questions about ecology, but in order to do that I need to know more about how these two local species interact with each other first.

In order to see which species is a better competitor for space, I set up 9 plastic cups, each with a little piece of Obelia covered in caprellids. After letting them fight for three hours, I counted how many C. laeviuscula were booted off the Obelia when it was just C. laeviuscula, compared to when I also had C. mutica in the cup. I found that when the invasive C. mutica was present, a lot more C. laeviuscula were kicked off the Obelia. This tells us that when we give the two species a limited amount of space, C. mutica is better at fighting for that space than C. laeviuscula. Despite C. mutica’s spines and C. laeviuscula’s poison tooth, none of the caprellids were killed, just displaced.


Except this guy, who was beheaded in a pilot experiment. Photo: Emily Lim

If you want to learn more about these weird, alien looking crawly things, check out this blog here!


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