Science Questions

Jelly fish swim in groups. How do they communicate to stay together?

Jelly fish swim in groups. How do they communicate to stay together or do they communicate? Steve

Helen -   I don’t think they do actually.  Jellyfish are in some ways extremely simple creatures.  They don’t have a brain, so they don’t really have the ability to process inputs and sensory inputs like that.  So, I think usually when you see large numbers of jellyfish together, it’s probably more likely to be, the fact that the currents and the ocean currents are actually moving them together and keeping them in similar places.  Or also, they can respond to things like the availability of food in the water and chemicals and things like that.  So possibly, they're all following food sources, and that’s why they're all ending up together.  But I don’t think we yet have an idea that jellyfish can actually communicate to each other.  Although some of them do have quite complex eyes, which is quite exciting and box jellyfish have eyes.  They're actually quite...

Chris -   What do they do with them?

Helen -   That’s a very good question.  They have eyes quite a lot like humans and in fact, some of the genes they have are very similar to human genes for creating parts of the eye, but we think that happens in parallel and wasn’t from a common ancestor, but we arrived at the same solution to having eyes and what do they see?  We know they certainly respond to daylight, light and dark.  They need to know basically, what time of day it is because they tend to come up the water column at nighttime when they're less easily seen by predators and when it’s light, they actually go further down the water column.  So, they respond to light and dark.  And even though they have quite complex eyes, it’s actually a very good eye at detecting things like diffuse light to figure out, is it light or dark?  What time is it?  Should I be up or down in the water column?

October 2009