How do deep sea creatures know the time?

Marine biologist Kate Feller took on this question from Laura...

Kate -  Biological clocks are so important to biology and it doesn’t matter if you live with or without light even though the primary genes that regulate circadian rhythms, as we call them, are light sensitive so they typically are regulated by light.

However, there are other cues that animals, for instance, in the deep sea can use in order to have some sort of cycle in their biological activity or just their physiology. And one of those is the activity of everyone living above them in the parts of the ocean that do receive light imput, what they’re doing. So every day, in all of the bodies of water in the ocean that have little tiny critters living in them, there is a mass migration that happens where they go to the surface at night to feed and then they come down to the darker depths during the day so that they can avoid being eaten by things at sea. It’s called the diurnal vertical migration.

When that happens, that activity of going up to eat and then going back down, when you got up to eat and you start eating you then start pooping, and so there are these kind of pulses in nutrients that can happen. You can also have seasonal variation in the amount of nutrients that are falling down just from phytoplankton blooms. So all of the plant type or all of the photosynthetic life that’s living in the ocean, it will change based on the season, and so that is another cue that you can use as a clock.

Chris - Right. So things that are sensitive to sunlight change their behaviour and this has like a domino effect where the repercussions of their activity changing ripple down in the water column to the dark depths where other creatures are then having their body clocks entrained by their stomachs effectively?

Kate - It’s literally all of the nutrients in the deep sea are coming from the surface from the things living above them.