Bioblog: Tempo of the Tides
by Julianne E. Steers, Marine Biologist and Director of Husbandry
As we welcome winter along the Southern California coast, we also welcome extraordinarily low tides. Anyone who has spent time along our beaches is certain to notice that the water level of the ocean does not stay the same all day long. The percussion of waves lapping upon the shore is consistent, though water levels change as the day passes. Water rises for several hours and then recedes. This rise and fall of the ocean is known as the tide. A tidal tempo is at the heart of the concert of the sea.
Imagine our earth completely covered with a layer of water, its movement fueled by the gravitational pull of the moon. As the moon rotates around the earth, its gravity pulls the water out into a bulge on the side of the planet nearest to it. The centrifugal force caused by the spinning of the earth causes the water to bulge on the opposite side of the earth. These bulges make the high tides. Halfway between these bulges, on each side, low tides occur.
If the earth was covered with water of the same depth, there would be two identical high and low tide cycles over the entire surface during a complete turn. However, the shape of our lands and the size, shape, and depth of all the estuaries, bays, seas, basins and more hamper with this perfect cycle. Therefore, the resulting coastal shorelines have two high and two low tide cycles each day, others only one, and still others a mixture.
The tidal range along the Orange County coast varies from one foot to over eight feet. This may not sound like much of a rise, but you must remember that this is the actual water depth. This means that on a fairly flat beach, the water can move onto the shore 30 feet or more.
A world of marine creatures exists in the “Kingdom of the Tides,” the area rocked by the incoming and outgoing waters and tides which plays an important part in the ecology of the coast. As the tide sweeps in, it covers our rocky and sandy shores, stirs up nutrients, and brings rich oxygen to stagnant pools that remain from the previous high tide. When the incoming tide brings its tasty morsels to wash over the tide pools, the mussels open up, anemone tentacles reach out, and crabs scurry about feasting on the ocean smorgasbord. Likewise, fish surf in on the incoming tides to feed in the shallows.
As the tide recedes, our coastal pools expose many wildlife notes. The diversity revealed is certainly the delight for any beach-goer turned scientist. From sea hares to urchins to sea stars in every nook and cranny, there is a chorus to be found. Take a stroll, investigate and dance to the rhythm of the tides this winter.
Julianne Steers is a marine biologist and the Director of Husbandry for the Ocean Institute.