Early work on coastal crustaceans in California showed nice 12.4h activity in tiny crustaceans (amphipods). Animals were kept in seawater tanks with sandy bottoms and photographed at regular intervals. Animals that emerged from the sand at each interval were counted and recorded. The figure shows the number of animals swimming over time. The upper graph shows the expected tidal cycle- tidal height in feet- at the home beach. The lower graph shows the number of amphipods swimming over time. Note the increased swimming activity coincides with expected high tide.