How pea crabs find their way home

As they prepare to metamorphose from larvae into adults, New Zealand pea crabs seek out the green-lipped mussels (and other bivalve molluscs) that will be their homes for the remainder of their lives. They rely on settlement cues – signals that help them locate mussels from a distance. In this video clip, Jessica Feickert (Leigh Marine Laboratory) describes her search for pea crab settlement cues.

Focus questions:

• Why might New Zealand pea crabs use chemicals from green-lipped mussels as settlement cues?

• Why might their settlement cues differ from other crabs that are non-parasitic?

Learn about the settlement cues (particularly sound) that non-parasitic crabs use to locate the rocky reef, in the article Crabs finding home.

Transcript

Jessica Feickert (Leigh Marine Laboratory)
Settlement cues are what the larvae use when they’re ready to settle and become an adult in their adult environment, and their whole aim is to try and find somewhere to settle and turn into an adult crab. So they go looking for green-lipped mussel beds especially. In order to find that habitat, they need to use cues, because they’re coming from open ocean to a really specific place. And these cues can be things like salinity for different species, sound cues – so the sound that their environment usually makes – or chemical cues or smell cues.

I wanted to see which settlement cues that my species use, so I started with an acoustic experiment to see if they’ll settle to a certain sound, because this is quite common in other reef crabs. So I tried them on silence, the sound of a sandy beach – and all you can hear is sand and surf – and also the rocky reef, which typically has mussels on them and all sorts of other animals.

If they respond to a cue positively, it means their time to becoming an adult will be shortened, and I found with the acoustic cues, there was no change at all between silent and beach and reef sounds. And I tried them on chemical cues as well and tried them on just plain seawater, UV filtered and things like that, and the other one with mussel-inoculated seawater. I didn’t get enough through to have a statistically significant result, but it did seem clear to me that they were responding to mussel-inoculated seawater.

Acknowledgements:
Jessica Feickert – Leigh Marine Laboratory, Auckland University.