The topography of the seabed around the islands is not unitary but rather complex. There are the topographical types of shallow seabed, gently sloping seabed, and accumulation seabed. Right at the depth of two meters types of coral are available and they are especially numerous in the depths from 10 to 20 meters. Coral covers over 60% of the seabed and they make seawater become cleaner. Long underwater valleys were formed as the result of the erosion of island foothills. The gullies located around islands (30 meters in depth or more) are the habitat of lobsters and mollusks living on stone cliffs.
Every island is almost a perfected ecological system with its specific geological scenery (for example forests, beaches, seawater, bright sunlight and spacious air). However, forests are very difficult to grow on islands. Although on islands they would be highly endemic, their development may take tens or even hundreds of years. Forests not only supply people wood as raw material but they are also a friend of people by preventing islands from land erosion and fresh water exhaustion and providing food to animals and plants. Most forest plants on islands are migratory plants coming from the mainland; some of them are herbs. 116 plant species on Cu Lao Cham Island are herbs, making up 22.8% of the total plant species. The thien tue tree on Cu Lao Cham and Hon Giai Islands is an endemic species listed in the Red Book. Thien tue trees 1-3 meters tall and one or two centuries old are growing as dense woods, making these islands attractive tourist spots. Though animals are not so abundant on the islands, the most popular types of them, for example squirrel, monkey, parrot and magpie, are available.
Only 10-20% of the total land area of the islands is arable soil. Mainly, it is feralite soil and sand that contain less humus and is poor in soil nutrients. The stream-cut gentle slopes of islands are covered by a thin layer of humus favorable for the growth of orchards, forest gardens and broadleaf trees. On the level surfaces at the height of 200-300 meters plants may be well developed. The climate on these level surfaces is typical of the sea and highlands (high humidity and mild climate). On some offshore islands like Hon Khoai, Cai Bau, Cu Lao Cham and Cat Ba ecological tourism may be developed and high-class resorts may be established without harming the environment.
The air on the sea and the islands is the cleanest. Biological diversity on the islands is great; however the quantity of each animal and plant species is not great because they are merely the tropical species, whereas the area of the islands is limited. Sea products are also highly local.
– Fishing around islands and in the sea depends on two vital factors. First, islands must be located near the traditional fisheries. Second, fishing technology must be of a high level and there must be pecuniary capital. Islands in Bac Bo Gulf such as Co To, Cat Ba, Vinh Thuc and Van Don can really promote exploitation of sea products and raising fish in sunken cages of medium scale.
This occupation, however, is very restricted on the islands of Central Viet Nam and South Viet Nam because natural conditions are not favorable.
2. Development potential
A. Islands of the North
Van Don Island District
Van Don archipelago is located to the east and northeast of Quang Ninh province. It rounds off the east and southeast of Bai Td Long Gulf and has about 600 large and small islands. Cai Bau, the largest island, occupies nearly half the area of the district. The capital of the district is Cai Rong town – 50 kilometers from Ha Long City and seven kilometers from Cda Ong town. To the southeast of Van Don is the Van Hai chain of islands, including the large islands of Tra Ban, Cao Lo, Quan Lan, Dong Chen, The Vang, Ngoc Vung and Canh Tuoc and other small islands. All these islands form a “curtain” sheltering Bai Tu Long Gulf.
Van Don is adjacent to the sea of Tien Yen district on northwest side; to the sea of Dam Ha district on the northeast side; to the sea of Cam Pha town on the west side; to the sea of Co To district on the east side; to Ha Long Bay on the southwest side; to the sea of Bac Bo Gulf on the south side.
The area of Van Don district is 551.3 km2. Twenty of the 600 islands of Van Don Island district are populated. The largest, Cai Bau Island (17,212 hectares), is located near Cam Pha town. All the islands rest on limestone terrain, often at 200-300 meters above sea level with lots of karst caves and grottos. The islands of Van Don, like all other islands in Bac Bo Gulf, formerly were mountainous peaks lifted from the continental shelf of the northwest region of Bac Bo Gulf. The peaks of Van Don are an expanded part of the Dong Trieu Mountain Range. These peaks were left behind after a period of marine transgression when Bac Bo Gulf was formed and since then have been floating on the sea, becoming isolated islands of the Bai Tu Long and Ha Long bays of the greater Bac Bo Gulf. The islands of Van Don are just part of the archipelago located in the northwest of Bac Bo Gulf. The most prominent mountain peaks on Van Don are Nang Tien at 450 meters in height (on Tra Ban Island in the territory of Ban Sen commune) and Van Hoa at 397 meters in height (on Cai Bau Island).

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