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Usually, you can expect the underwater terrain at the dive site to be an extension of the shoreline. If the shore is rocky and rugged, you will probably find similar underwater conditions. A wide, sandy beach usually indicates a vast expanse of sand offshore. There are exceptions, so it helps to check with other divers regarding an unfamiliar site. Some information about bottom conditions is also available on navigation charts used for boating. In most cases, the greater vertical relief (wall) there is to a dive site and the more aquatic plants present, the greater the amount of marine life in the area (figure 8-9). Flat stretches of bottom tend to be lacking in readily visible life compared with kelp forests and coral reefs. Divers tend to seek areas with plenty of marine life to be seen, which makes diving more interesting. You find many different bottom compositions under water. These include mud, silt, clay, sand, pebbles, rocks, and coral. Mud and silt bottoms are easily stirred up. This can reduce visibility to zero because of suspended sediment. Sand bottoms have better visibility, but these tend to be underwater deserts visually, because most of the life is in and under the sand, or flees at your approach. Rocky Chapter 8- Diving Environment bottoms provide a good base for marine plants and provide many holes and crevices that aquatic animals use as homes. Aquatic plants do not grow well in tropical waters, but coral thrives in these waters and provides excellent diving. Barnacles, rocks, and underwater formations might have sharp edges, so you must have good buoyancy control to prevent cuts and scratches when diving in areas with these features. Varying bottom compositions require different diving techniques. You must learn one technique for a beach entry on a sandy bottom that provides good footing and another for a muddy bottom, which can pose an entirely different set of challenges. Mud can also be very slippery when you are entering or exiting the water. Once you have entered the water, you will find that you must move carefully to avoid stirring up a muddy or silty bottom. Sandy bottoms do not cloud the water as easily as muddy or silty bottoms. Coral and rock reefs usually provide the best visibility as well as many interesting things to see. Once you begin diving in open water, you will better appreciate the ways bottom composition is one of the many elements that affect your dive. Diving Environment 179 FIGURE 8-8. ALWAYS GET AN ORIENTATION TO A NEW AREA FROM AN EXPERIENCED DIVER WHO KNOWS THE AREA. FIGURE 8-9. ROCKY AREAS HIDE MANY MARINE CREATURES.


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