Wave Swept Shores:
By Michael Boller

The wave-swept rocky shore is a dynamic, physically stressful place to live. Organisms are baked and dried out in the sun during low tides (see Sizzling on the Seashore) and battered by the waves crashing right onto the rocks. Here at in the Hopkins State Marine Reserve, the Denny Lab has been observing and measuring wave heights, forces, and velocities for years. In that time, we’ve documented peak velocities as high as 35 m/s (78 mph) from waves topping 5 m (16 ft) in height! The normal velocities that organisms have to deal with are generally around 5 to 6 m/s, but wavy days can increase that to 10 to 15 m/s. Anyway you look at it, the mussels, urchins, seastars, limpets, snails and algae all need to hang on tight to survive.

Recently, we’ve moved into a new generation of wave measurements. We’ve designed and built self-contained, miniature wave force dataloggers, called “WaveLoggers,” to measure each and every wave at a rate of 100 samples per second (a big improvement over the spring scale Dynamometers). The brain of each Wavelogger (on the right) consists of an Atmel ATMEGA8 microcontroller and several FLASH memory chips. This minicomputer keeps track of the time of each wave, handles the analog to digital conversions, decides when to record the waves, and manages the battery life (for extended deployments up to two weeks). Instrumentation amplifiers condition the force signal that is made when waves strike the white ball that is attached to the force transducer. With these devices we can record each wave that breaks on the study site and extract the magnitude, frequency, and duration of forces. These data enable us to have a much more detailed view of what organisms must deal with on a daily basis, whether they are crabs and snails coming out of their shelter for a quick snack between waves or algae that need to resist each and every wave (see Death by Small Forces).

Wave logger insides

Log from Wave Logger:

Length of arrow indicates magnitude. Compass indicates the direction of wave force. Time slowed to 1/4 speed.