Mestrado/Master’s research

Tethering juvenile crabs

As part of my master, I decided to assess predation on juvenile fiddler crabs (Genus Leptuca) using tethering technique.

This technique consists on fasten an animal to a line attached somewhere on field in order to assess something, like predation rates. It is widely used on “large” animals, such as the blue crab, but on smaller animals is harder to find information on how to make the technique work without killing the individual by manipulating it.

At first I found some problems to make the tethering technique work and here comes my adversities and my solution to it.

The inviduals are fast so is hard to hold them, and I’m likely to kill them by trying or to glue the line elsewhere, like a leg or an eye. I tried to anesthetize them with mentol, but it took time and I needed to be fast so I would be able to do more replicates. Then, I tried to put ice on the water, but it only worked while the individuals where inside the water. As soon as I took them of the ice they woked up and were wet, while I needed them to be dry for the glue to work. I tried to put the Petri dish above an ice plate, but the crabs died very fast. All that on field. At last, I tried to put the individuals on refrigerator at the station for just the amount of time for them to stop moving. I found that 5 minutes were enough, but they still started moving quite fast, so I puted them individualy on the refrigerator and took them out one at a time.

Once I managed to glue the juveniles properly I was able to set a pilot on field. Images above show how it looked like. On the left there is a juvenile fiddler crab glued to a fishing line and on the right the line with predation marks.

We compared tethered juveniles predation within saltmarshes and on bareflats. Results from this research were published on Marine Environmental Research journal.