ISLANDS AND CORAL REEFS

1. Island

An island is a body of land surrounded by water. Continents are also surrounded by water, since they are very big, they are not considered as islands. The island can exist as a single one or as a group in the ocean The following are the types of islands in general. 

1. Volcanic islands: these islands occur in ocean basins or near oceanic ridges. These are large volcanoes which are erupted and they have risen above sea level
2. Coral reef islands: these are very low islands which emerge just above the water level. These islands are built up by coral animals of various species

Coral reefs are the most diverse ecosystem in the world. Coral polyps which are primarily responsible for building reefs, can take many forms. Some live in warm, tropical seas climate and others live in cold, dark depths of the ocean.  Coral reefs have a set of conditions that they need to survive. When it comes to it, coral reefs are fairly finicky organisms- if the following conditions aren’t met, they will be stressed, diseased and even die

1. Clean water: when polluted water and wastewater enter into marine systems, they carry chemicals with them which help grow algae. Algae is harmful to coral reefs, hence clean water is important
2. Warm water: Most hard coral reefs prefer the range of 73° to 84° Fahrenheit (23 to 29 Celsius). Some corals can tolerate the heat as low as 20°c(68F) and high as 32° (80F)
3. Healthy wildlife population: Many coral reef animals play an important role within the coral reef system. For example, herbivores like parrot fish and sea turtles graze on algae and help to keep the algae population In control. When the herbivore population declines, the coral reef population can be overtaken by algae. 

• The most common type of reef is fringing reef; this type of reef grows seaward directly from the shore. They form borders along the shoreline and surrounding islands
• When a fringing reef continues to grow upward from a volcanic island that has sunk entirely below sea level, an atoll is formed. Atolls are generally circular or oval, with an open lagoon in the centre
• Barrier reefs are similar to fringing reefs in that they also border a shoreline. Instead of growing from the shore, these are separated from land by an expanse of water