Hawaiian Shell News
An Educational publication of the
Hawaiian Malacological Society

Mollusks of Guam & Yap
Introduction & Comments
Wesley M. Thorsson
30 January, 1994

This set of volumes provides photographic and written descriptions of the common shells of Guam and Yap reef flats and the environment in which they are found. Guam and Yap are high islands separated by about 432 nautical miles. Guam has a fringing reef 0.2 to 0.5 miles wide in many areas. The northwest and northeast coasts have a narrower reef. The east coast is often lava reef while the west coast has a coral (or dead coral) reef in general. Trade winds from the northeast make the east coast more subject to wave action. Apra harbor on the central east coast is a major deep water port well protected by a manmade breakwater on the north side and is usually calm. Cocos Lagoon on the south west tip of Guam encloses a wide coral area with Cocos Island part of the fringing reef. Most reef flats are fairly shallow with the coral grown to within a foot or two of the surface at low tide. There are usually extensive rubble areas exposed at low tide and sand is usually found near shore and in areas between coral. Hard and soft corals of many species are to be

Yap is a group of small islands that are closely spaced and has a fringing reef of about a mile wide with frequent blue water holes which may be 30 feet or more deep. There are also a number of channels that cut through the reef. The channel into the capital, Colonia, supports moderate sized ships. The reef areas are generally shallow, a foot or two deep at low tide. Some have good coral areas near shore while others are subject to silt deposits from rivers and are silty sand and algae areas. The deep holes generally have extensive coral formations. Channels through the reef are usually quite shallow and silty near shore.  In many areas there is extensive mangrove growth. In view of the shallow reef and canals, traditional travel was by bamboo rafts with only a few inches draft. Modem Yap includes good paved roads to major areas, dirt roads to most villages and trails to less populated  places. 4-wheel drive is recommended as the red clay is quite slippery after the frequent rams.

My collecting activities for this trip by my wife, Elizabeth Thorsson, and myself were during the period of 13 July, 1993 to 3 August, 1993, primarily spent on Guam, snorkeling on a number of different reef locations each day for 1 to 5 hours. Almost all snorkeling was inside the reef edge unless otherwise stated m station descriptions. Betty collected a

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