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The Tide Pools of Okinawa
Date Posted: 2000-10-27
One of the most fascinating aspects of any visit to the ocean, at low tide, is an exploration of the tide pools. Tide pools are pools of water that remain on shore after the ocean recedes at low tide. Tide pools are caused by the gravitational pull of the moon. Because high tides follow the revolutions of the moon around the earth, tide pools are formed.
Tide pools have many different sizes and shapes. They can be very small like a small pond of water, or they can be large like a small lake. Their depth can range from just a few inches to several feet. Because of their diversity in size and depth, tide pools are capable of supporting many types of life, from protozoans, fungi, coral, and plants, to sponges, echinoderms, mollusks, and fish, just to name a few. This writing will discuss the physical aspects of tide pools, the environmental conditions, and the animal and plant life in the tide-pool environment of Okinawa.
The tide pools of Okinawa are very diverse. One aspect of their diversity is their floor type, called a substrate. Some tide-pool floors are sandy, some are rocky, and some consist of sand and rocky rubble. The sand on the bottom of Okinawa's tide pools is light brown on the top, but if one digs a few inches beneath the floor, the color of the sand turns black. This is caused by anaerobic decomposition. Anaerobic decomposition is the result of decomposition of animal and plant life beneath the sand where there is no oxygen.
If you take a very close look at the sand, you will find some that are star-shaped. Actually, the star shaped sand is made up of foraminiferans, single celled protozoans. Because their shell is composed largely of calcium carbonate, they blend in very well with the calcium-carbonate sand which is plentiful around coral reefs.
The type of life that exists in the tide pool depends a lot upon the tide-pool's floor. Some animals, like sea cucumbers, filter sand from the bottom into their digestive tracts. Consequently, animals like sea cucumbers that filter sand to survive can be found on the sandy bottoms of tide pools. Another animal that thrives in a sandy bottom environment is the dolla bella, commonly called the sea hare. Sea hares resemble a Spanish Conquistador's helmet but instead of shiny brass like in color, they are light tan which matches the sandy surfaces that they inhabit. They excrete a deep-purple liquid when disturbed to distract their enemies.
Some animals, such as sea urchins, prefer to hang out in the rocky areas of tide pools. Sea Urchins like rocky surfaces because rocks provide a good location for their favorite food, algae. Algae grows best on the rocks because the rocks hold fast, in one location, when the surf arrives. Because algae is the urchin's favorite food, sea urchins can easily be found in rocky tide pools. Another type of animal that often occupies the rocky surfaces of tide pools is the brittle star. Brittle stars like to filter feed organisms that inhabit tide pool floors. Brittle stars are found often near the sand but at the same time they stay close to rocks for security. When touched by a predator, brittle stars cling to the rocks for survival. Brittle stars have the ability to regenerate limbs. If a predator bites off one of the brittle star's legs, the brittle star will regenerate another leg in its place.
Sand and rocky-rubble floors are a good place to find fish, eels, crustaceans, and seaweed. A common fish that can be found in the rocky rubble of tide pools is the mud skipper. The mud skipper's colors enable it to blend in well with the bottom of a rocky-rubble tide pool. Although it is not a real high-class swimmer, the mud skipper has mastered the art of camouflage.
Two other animals, both crustaceans that have mastered the art of hiding in rocky-rubble tide pools are the box crab and the decorator crab. Box crabs hide themselves by burrowing a hole in the sand and burying themselves up to the point that only their eyes are exposed above the ground. Decorator crabs take a different approach to camouflaging themselves. They attach debris, such as rocks, coral, and pieces of shell, to their body and appendages, which gives them the appearance of being part of a rocky rubble bottom. Seaweed grows best in a rocky rubble environment. Seaweed needs the rocks to anchor its roots to the ocean floor.
Because of their diversity, tide pools have many different environmental conditions. Environmental conditions are those factors that affect life in tide pools. One environmental condition of tide pools is their depth. If a tide pool is very shallow, many animals have a very difficult time surviving. Reduced survivability is because of a number of reasons. First, because the sun heats up the water faster in a shallow tide pool, there is less oxygen for the animals to breath. Consequently, small and shallow tide pools that are located furthest away from the surf are the least likely to sustain animal life. That is why very few amounts of coral can be found in shallow tide pools.
Another reason that shallow tide pools are dangerous to many animals is that they provide an easy access for predators such as crabs. Although crabs generally are thought of as scavengers, they won't hesitate to opt for a fresh fish dinner if they can get the chance. Another creature that often upsets the balance of life in tide pools is the human being. While tide pools are exciting to view, turning over rocks exposes marine wild life to sunlight. Sunlight often has a devastating affect on the animals and plant life that flourish beneath the rocks.
Still another reason that small shallow tide pools are very dangerous for animal life is fertilizer runoff. Because many people grow crops near the ocean, fertilizer runoff poisons the water of many tide pools. The smaller the tide pool, the greater the chance that fertilizer runoff will pollute the water.
Large tide pools, on the contrary, support a much greater variety of life. Some fairly deep tidal areas have water that is over ten feet deep. Those tide pools remain close to the surf at low tide. In these deep tide pools, many types of corals can be found. Additionally there are hydroids such as Stylaster Coral, black sponges, red coral, coraline algae, worms, crustaceans, mollusks, and various types of tropical fish. Life in the large tide pools is much more abundant than in the small tide pools.
This writing discussed tide pools. I discussed where tide pools are located, their sizes and shapes, and the environmental conditions that affect life within them. I also touched upon the types of life that inhabit the tide pools and the conditions that help to influence whether life either banishes or survives. No two-tide pools are the same. Each is unique. Each has its own individual attributes and each has a different story. Tide pool exploring is an exciting way to learn about the world in which we live.