We’re surrounded by alarm clocks these days. They’re on our bedside tables, our computers, and our phones — electronic reminders to get up and get going. But perhaps our most important clock is a biological one — an internal system that regulates how our bodies work, tied to the 24-hour rhythm of night and day.
A speckled sea louse. Credit: Hans HillewaertThe creatures that live along the shore appear to have two internal clocks. One is linked to the cycle of night and day, but the other is linked to the tides — a cycle that lasts about 12-and-a-half hours.
Since that cycle is a bit more than half of the length of a day, biologists have wondered whether organisms that live in the tidal zone have two separate biological clocks, or one clock that works two half-day shifts.
A recent study by researchers in the UK suggests it’s two separate clocks.
They studied the speckled sea louse — a tiny crustacean that shows different behaviors related to the day and the tides. It changes color from day to night, for example, and it comes out of the sand when it’s time for the tide to come in.
The researchers used various methods to isolate the two cycles. They found that even when you turned off the 24-hour internal clock, the clock related to the tides continued to tick — the little creatures continued to swim vigorously when it was time for the tide to roll in.
The work suggests that many of the creatures that live in the tidal zone operate to the rhythms of two separate internal clocks.
