Coral Reef Formation and Threats: A Comprehensive Overview

1. The majority of reef building corals are found within tropical and subtropical waters. These typically occur between 30 north and 30 south latitudes. The red dots on this map show the location of major coral reefs of the world

2. The individual coral polyps are joined together The coral skeleton has a ridged or pitted surface Mouth Tentacle STEP

3. Here is a good example of a live coral.

4. The Great Barrier Reef

5. Requirements for Reef Formation • High Light Levels • High Water Transparency • Water Temperatures > 20°C • Low Nutrient Waters • Hard Substrate for Attachment • Good water circulation Coral reefs grow in shallow water along the coast and around islands

7. In some places, the level of the sea has risen Here, the coral reef continues to grow, forming a ring around the island

8. Atoll Formation: Step by step

9. Sea level STEP

10. Top of the original island - now nearly below sea level New coral islands form on top of the reef Shallow, sandy area between the reef and the island Reef grows upwards as sea level rises STEP

11. Atoll Reefs: Volcanic Left-overs!

12. Atoll Reef Fulanga

13. Coral reefs begin to form when free-swimming coral larvae attach to submerged rocks or other hard surfaces along the edges of islands or continents. As the corals grow and expand, reefs take on one of three major structures Fringing reefs, Barrier reefs or Atolls

14. As the reef expands, the interior island usually begins to go under water due to sea level rise and the fringing reef turns into a barrier reef. The process of atoll formation may take as long as 30,000,000 years to occur. Fringing reefs are the most common and they project into the sea from the shore, forming coral edges to islands It can take 10,000 years for a fringing reef to form Barrier reefs are also next to shorelines but further away. They are separated from land by a lagoon of deep water. Atolls are usually circular or oval, with a central lagoon. Over the next 100,000 years the fringing reef will expand. If a fringing reef forms around an island and the island goes completely below sea level while the coral continues to grow upward an atoll forms. Corals begin to settle and grow around an oceanic island – the start of a fringing reef. When the island completely subsides beneath the water leaving a ring of growing coral with an open lagoon in its center, it is called an atoll.

15. One of the most significant threats to reefs is pollution. Land-based runoff and pollutant discharges can result from dredging, coastal development, agricultural and deforestation activities, and sewage treatment plant operations. This runoff may contain sediments, nutrients, chemicals, insecticides, oil, and debris. There are many ways that pollution can damage reefs. Debris like this plastic bag can quickly become entangled on a coral and smother it.

16. Examples of Human Factors Affecting WorldwideDecline of Corals – put into order worst to least worst effect,. • Overfishing• Nutrient over-enrichment (farming) • Starfish?• Increased sedimentation• Population increases• Shoreline development• Trampling by tourists• Ship accidents• Destructive fishing methods