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Ecology

Fighting the Tide

The Pacific coast landscape changes radically every six hours, creating an ecosystem as unique as its varied inhabitants. The creatures that live here spend six hours submerged under the sea and six hours on land, exposed to high temperatures in the open. They battle strong waves and currents every time the tide comes in or goes out.

Text and Photos: Javier Pinzón

The Earth spins on its axis at approximately 1,000 miles per hour. This means that its position relative to the Moon changes every six hours, altering the pull of gravity exerted on the Earth by our satellite. We humans don’t feel this gravitational pull, but these movements do affect other living beings. The plants and animals inhabiting inter-tidal zones must synchronize their lives with the rising and falling tides.

I am standing on a typical Panamanian Pacific coast beach at six in the morning. To my left lies a labyrinth of rocks that defines the coastal zone; in front of me, a broad white sand beach stretches ahead like a desert; and to my right, mangroves reveal their roots as if a giant hand had brushed away all the sand. It is low tide and the sea has dropped some fifty feet. On a flat coastline like this one, the water recedes nearly 2,000 feet from the shells marking the high-tide line. This is the inter-tidal zone.

The Panamanian Pacific is one of those places where the effects of Earth’s rapid rotation and the Moon’s gravity are very visible to the casual observer. This phenomenon allows us to walk along the seabed and take a close look at creatures that have adapted to life in extreme and frequently changing conditions.

At low tide, these animals must endure high temperatures and extremely saline environments. As the tide rises or falls, they battle strong waves and currents. At high tide, they are completely submerged beneath the sea. While life may be difficult here, a large number of hardy creatures flourish in this zone.

Small salt water pools form in crevices among the rocks. High tropical temperatures warm these pools quickly and much of the water evaporates during low tide, creating a very hot, saline environment. The pools commonly host small anemones, assemblies of snails, and the occasional fish seeking refuge as the water retreats. The rocks are carpeted with living creatures: limpets, oysters, barnacles, and myriad mollusks that draw back into their shells during low tide, but come out to feed on the abundant plankton when the water returns.

The expanse of sand, a seabed in the sun, is home to sand dollars; they are cousins to starfish but with the unusual appearance of a huge coin. These creatures have tiny feet that help them glide along the sand, leaving distinctive tracks. The sand dollars burrow beneath a fine layer of sand to await the changing of the tide. Segmented worms poke out of the sand. They build long tunnels under the beach, exposing only part of their bodies and covering themselves with shells as camouflage.

Hermit crabs roam across the sands in a seemingly aimless fashion. These crabs have no shells of their own, so they repurpose shells shed by snails, continually replacing the shells as they grow. Low tide sees the emergence of fiddler crabs; the male of the species builds small roofed houses to attract females. Fiddler crabs are responsible for the long trails of sand balls that typically mark Panama’s Pacific beaches. Meanwhile, a wide variety of mollusks, such as clams, emerge from their hiding places under the sand when the returning water brings their supper of plankton.

Low tide also makes it possible to stroll under a canopy of mangroves. These trees tolerate extremely high levels of salinity and their root systems shelter many animals. Unlike their forest cousins, the trunks and roots of these trees are shrouded with marine animals like snails and barnacles, and serve as rest stations and shelter for hermit crabs. They also make a favorite rest stop for many birds, which feed on the clams and segmented worms hidden in the sand.

It is now noon and the landscape has altered dramatically. The rock garden that was on my right has practically disappeared, leaving only small islands of rock. The vast beach that stretched nearly to the horizon is completely submerged and the water now reaches the shell line at my feet. To my left, the mangrove roots are likewise submerged. Only a few green treetops hold their heads above water. The fish have arrived, providing an underwater bounty for marine birds, pelicans, and frigate birds. The water has risen some sixteen feet in just six hours, and the 2,000-foot beach of the morning has ceased to exist. Everything will change again in another six hours and the unvarying routine continues day after day. The cycle repeats every twelve hours, but each day it happens forty-five minutes later than the previous day.

It is not only the animals of these regions that live by the cycle of the tides, which correspond to the moon’s phases. The schedules of coastal communities, which include fishers, athletes, divers, and seafarers, are also linked to the tides. Boats can go out to sea only at low tide on some beaches, while high tide is a better time on others. Tourism and water sports must also take the tides into account. Some beaches offer better swimming at high tide, while it is better to wait for low tide at others. Surfers prefer the strong waves generated by the changing of the tide, and paddle boarders follow the tides as well. Some diving sites are better at low tide because they are shallower then, while others are less exposed to the waves at high tide. Pacific coast life revolves around the tides, offering a landscape that changes hour by hour.