Coral Reefs - Part 1: Location, Characteristics and Development of Coral

Source: https://science.nasa.gov/earth/climate-change/vanishing-corals-nasa-data-helps-track-coral-reefs/

Coral reefs are among the most remarkable ecosystems on Earth. Known for their vibrant beauty and biological diversity, they are often referred to as the "rainforests of the sea." For geography students, coral reefs offer an excellent opportunity to study biogeography, physical processes, and human-environment interactions. 

Locations of Coral Reefs Around the World

Source: https://encounteredu.com/multimedia/images/map-of-the-worlds-coral-reefs

Coral reefs are predominantly found in tropical and subtropical regions between 30° north and south of the equator. They thrive in shallow, warm waters of the oceans, where temperatures typically range between 23°C and 29°C. The three main types of reefs—fringing reefs, barrier reefs, and atolls—are located in distinct regions around the globe.

The Indo-Pacific Region

This region encompasses the largest concentration of coral reefs, stretching from the Indian Ocean to the western and central Pacific Ocean. The Coral Triangle, which includes the waters of Indonesia, Malaysia, Papua New Guinea, the Philippines, Timor-Leste, and the Solomon Islands, is often regarded as the epicentre of coral biodiversity. The Great Barrier Reef off Australia’s northeast coast is the largest coral reef system in the world, spanning over 2,300 kilometres.

The Atlantic and Caribbean Region

Coral reefs in this region are smaller but still significant. The Mesoamerican Barrier Reef, located along the coasts of Mexico, Belize, Guatemala, and Honduras, is the largest reef system in the Atlantic Ocean. Other notable locations include the Florida Keys in the United States and various reefs in the Bahamas and the Lesser Antilles.

The Red Sea and Indian Ocean

Coral reefs in the Red Sea are known for their resilience to extreme conditions, including high salinity and temperature. In the Indian Ocean, reefs can be found off the coasts of East Africa, the Maldives, and the Seychelles.

Characteristics of Coral Reefs

Coral reefs are primarily constructed by colonies of tiny animals called coral polyps, which belong to the phylum Cnidaria. These polyps extract calcium carbonate from seawater to build protective skeletons. Over time, these skeletons accumulate, forming the foundation of the reef. Here are some key characteristics of coral reefs:

Structure	Coral reefs have a three-dimensional structure that provides habitat and shelter for a multitude of marine organisms. Their complexity supports biodiversity by creating niches for species ranging from tiny plankton to large fish.
Biodiversity	Coral reefs host an estimated 25% of all marine species, despite covering less than 1% of the ocean floor. They are home to fish, molluscs, crustaceans, echinoderms, sponges, and algae, among others. Symbiotic relationships, such as the one between coral polyps and zooxanthellae (a type of photosynthetic algae), are critical for reef health.
Colour and Composition	The vibrant colours of coral reefs are largely due to the zooxanthellae living within the coral tissue. These algae not only provide energy to the corals through photosynthesis but also give them their distinctive hues.
Fragility	Coral reefs are highly sensitive to environmental changes. Threats such as rising sea temperatures, ocean acidification, overfishing, and pollution can lead to coral bleaching and the degradation of reef ecosystems (more on this in the Part 2 article).

https://www.youtube.com/watch?v=ZiULxLLP32s&t=52s

Conditions for the Development of Coral Reefs

The formation and growth of coral reefs are dependent on specific environmental conditions that have remained relatively stable over geological time. These include:

Warm Water Temperatures	Coral reefs require a narrow temperature range of 23°C to 29°C. Temperatures below or above this range can stress coral polyps, leading to bleaching events. This is why coral reefs are generally absent in colder waters or regions with significant seasonal temperature variation.
Shallow Waters	Corals rely on sunlight to thrive due to their symbiotic relationship with zooxanthellae. Sunlight penetrates only the upper layers of the ocean, meaning reefs are typically found at depths of less than 50 metres.
Clear Waters	Sediment and pollutants in the water can block sunlight, hindering photosynthesis. Therefore, coral reefs flourish in waters that are clear and low in nutrients, which reduces competition with algae for space and resources.
Stable Salinity Levels	Corals require stable salinity levels, as significant fluctuations can harm polyps. They are generally found in marine environments with salinity levels around 35 parts per thousand, avoiding areas with high freshwater input, such as estuaries.
Low Nutrient Levels	Paradoxically, coral reefs thrive in nutrient-poor waters, which limit the growth of algae that could otherwise outcompete corals. The nutrient cycle within the reef ecosystem is highly efficient, with waste products from one organism serving as resources for another.
Wave Action & Sediment	Wave action plays a significant role in shaping coral reefs. Moderate wave activity helps to oxygenate the water, remove waste, and transport nutrients to the reef ecosystem. However, excessive wave energy, such as that generated by storms or hurricanes, can physically damage coral structures by breaking them apart or burying them under debris. On the other hand, areas with minimal wave action may accumulate sediment, which can smother coral polyps and block sunlight, hindering photosynthesis. Sedimentation from land runoff, often exacerbated by deforestation and poor agricultural practices, further threatens reefs by increasing water turbidity. For example, studies in the Great Barrier Reef have shown that increased sedimentation reduces coral recruitment and growth rates (Fabricius, 2005).
Time	Coral reefs develop slowly, often taking thousands of years to reach their current forms. The Great Barrier Reef, for example, is estimated to be over 500,000 years old, with its current structure forming over the past 8,000 years.

https://www.youtube.com/watch?v=nBO7zWO1zXY

Some amazing types of coral!

Source: https://oceana.org/marine-life/grooved-brain-coral/

Brain Coral 

Description: Brain corals are named for their appearance, which resembles a human brain. They are dome-shaped and have grooves and ridges across their surface.

Characteristics:

- Size: Can grow up to 1.8 metres in diameter.

- Habitat: Common in shallow waters of the Caribbean and Atlantic Oceans.

- Role: Provide structural support for reefs, offering shelter for small marine creatures.

- Adaptations: Highly resistant to wave action due to their robust, rounded structure.

- Threats: Susceptible to coral bleaching and disease, particularly white plague.

Source: https://seaofchange.com/creature-feature-staghorn-and-elkhorn-corals/

Elkhorn Coral 

Description: This species gets its name from its antler-like branches. Elkhorn coral creates large thickets that are crucial for reef-building.

Characteristics:

- Size: Branches can grow over 2 metres in length.

- Habitat: Found in shallow tropical waters, especially in the Caribbean.

- Role: Acts as a barrier, reducing wave energy and protecting coastlines.

- Adaptations: Rapid growth allows it to recover from damage quickly.

- Threats: Highly vulnerable to temperature changes, disease, and storm damage.

Source: https://en.wikipedia.org/wiki/Staghorn_coral

Staghorn Coral 

Description: Staghorn coral has thin, cylindrical branches that grow in all directions, forming intricate thickets.

Characteristics:

- Size: Branches can extend up to 2 metres.

- Habitat: Found in the Caribbean and Atlantic Oceans, preferring clear, warm waters.

- Role: Provides habitat for fish and invertebrates.

- Adaptations: Can regenerate quickly after minor damage.

- Threats: Suffering from a dramatic decline due to coral bleaching, white band disease, and overfishing.

Source: https://www.bransonswildworld.com/bubble-coral-plerogyra-sinuosa/

Bubble Coral 

Description: This unique coral species has soft, bubble-like sacs, which make it stand out from the typical hard corals.

Characteristics:

- Size: Colonies can grow up to 50 centimetres in diameter.

- Habitat: Found in sheltered lagoons and reef slopes in the Indo-Pacific region.

- Role: Provides shelter and protection for small reef organisms.

- Adaptations: The bubble-like sacs expand during the day for photosynthesis and retract at night to expose tentacles for feeding.

- Threats: Sensitive to water quality changes and physical disturbances.

Source: https://en.wikipedia.org/wiki/Fire_coral

Fire Coral 

Description: Despite its name, fire coral is more closely related to jellyfish than true corals. It has a smooth surface with small pores and delivers a painful sting upon contact.

Characteristics:

- Size: Can form plate-like structures or grow as branches, reaching several centimetres to over a metre.

- Habitat: Found in tropical and subtropical waters worldwide.

- Role: Enhances reef complexity, supporting marine biodiversity.

- Adaptations: Possesses nematocysts (stinging cells) for defence and capturing prey.

- Threats: Vulnerable to ocean acidification and damage from human activities.

Vital ecosystems

Coral reefs are vital ecosystems that support immense biodiversity and provide numerous benefits to both the environment and human societies. They are home to around 25% of all marine species despite covering less than 1% of the ocean floor. Reefs act as natural barriers, protecting coastal areas from erosion, storm surges, and flooding by absorbing wave energy. They also play a crucial role in the carbon cycle, storing carbon dioxide and helping regulate the Earth's climate. Economically, coral reefs are invaluable; they support fisheries, provide resources for medicine, and attract millions of tourists annually, generating significant income for local communities. Moreover, they serve as a natural classroom, fostering research and education about marine life and climate change. However, their survival is under threat from climate change, pollution, and overfishing, highlighting the urgent need for conservation efforts to protect these essential habitats.

Extra sources:

https://www.youtube.com/watch?v=dKEvls3s1N0

https://www.marinebio.org/creatures/coral-reefs/#google_vignette