Coral reefs- its types and distribution

Introduction • Belong to the Phylum: Cnideria, Class: Anthozoa

• Under water structures made from CaCo₃

• Colonies of tiny animals called polyps or coral polyps

• Polyp- like a tin can open at just one end; has mouth surrounded by a ring of tentacles

• Have stinging cells or nematocysts

• Feeds on zooxanthellae

• Nematocysts help coral catch food

• They also help protect the coral

• When the cell is stimulated, it releases a sharp barb

• The barb will fire and catch the food and bring it back towards the mouth

• Symbiotic relationship

• Zooxanthella is an algae that lives in the skin of coral

• Coral provides protection

• Zooxanthella provides food and color!

• Algae receive protection and nutrients (carbon dioxide, nitrogen and phosphorus)

• Algae supply amino acids, fatty acids, and sugars to the corals.

• Principal organism- Hard corals

• Planula larvae settles down and attaches itself to hard substrate

• Larvae develop into coral polyp

• Secrets calcium carbonate around its body

• Colony grows by asexual reproduction

• Some polyp develops gonads and able to reproduce sexually

• Secretes hard exoskeleton- support and protect their bodies

• Grow best in warm, shallow, sunny, clear, agitated water

• Referred as ‘rainforests of the sea’- diverse ecosystem

• Occupy less than 1% of the world ocean surface

• Home for 25% of the all marine species

• Annual global economic value- US$ 375 billion

Zonation of coral reefs• Reef front/ fore reef- on the

seaward side,rise of reefs from lower depth of ocean to just or just below the surface of water

• Reef drop off- the slope of this front forms a vertical wall

• Spur & groove formation-reef front usually form a finger like arrangements; breaks the wave energy & prevents the damage

• Grooves are sand filled; allow sediment to channel down & away from coral reefs

• Reef crest- highest point of reef

• Reef flat/ back reef-portion which is more inward to land; area is having high variability, made up of rocks, sand etc

• Reef ends at shoreline or descends into lagoon

Specific features

• Temperature: 26-27C – Depth: Less than 80 ft to

230 feet– Salinity: Normal salt levels

(35ppt)– Light: Zooxanthellae need

light to survive– Sedimentation: Being

covered with silt interferes with photosynthesis

– Desiccation: being exposed to air. The corals will die if exposed too long

• Coral likes areas with lots of waves:– They are strong enough to

withstand the pressure– New water means more food– Waves remove silt– New water brings more oxygen

300N and S of the equator

Types of coral reefs

• Fringing reef- directly attached to a shore or borders it with an intervening shallow channel or lagoon Eg: Greater Caribbean region

• Barrier reef- separated from a mainland or island shores by deep channel or lagoon Eg: Great Barrier Reef

• Atoll reef- more or less circular or continuous barrier reefs extends all the way around a lagoon without a central island Eg: The Pacific Ocean

Other reef types

• Patch reef-common, isolated, comparitively, small reef usually within a lagoon or embayment; often circular, surrounded by sand or seagrass

• Apron reef- short reef resembling a fringing reef, but more sloped, extending out and downward from a point or peninsular shore

• Bank reef- linear or semicircular shaped; larger than patch reef

• Ribbon reef- long, narrow, possibly winding reef, associated with an atoll lagoon

• Table reef-isolated atoll type without a lagoon

• Habili- Specific to red sea; does not reach the surface, near enough to cause visible surf

• Cays- small, low elevation, sandy islands formed on the surface of coral reefs from eroded material, forms an area above sealevel

• Seamount or guyot- formed when coral reef on volcanic islands subsides

• Top of seamount- rounded; guyots-flat

Hermatypic corals & Ahermatypic corals

• Hermatypic corals- storny corals; obtain energy from zooxanthella

• Secretes hard exoskeleton

• Have 6 or fewer lines of symmetry-hexacorallia or zoantharia

• Scleractinia, Millepora, Tubipora and Heliopora

• Ahermatypic corals- have no zooxanthella, soft corals

• have eight tentacles –octocorallia

• flexible, undulating in the current, and often are perforated, with a lacy appearance

• skeletons are proteinaceous

Distribution of coral reefs• Estimated to cover 284300 km²

(0.1% of ocean surface)• Indo-pacific region (Red Sea,

Indian Ocean, Southeast Asia & Pacific Ocean) -91.1%

• Southeast Asia accounts-32.3% • Pacific including Australia

accounts-40.8%• Atlantic and Caribbean corals

accounts- 7.6%

• Location of coral reef in the world

Global distribution

Distribution of coral reefs in various oceans

• Persian Gulf and Red Sea- contain a small percentage of world’s coral reefs

• Indian Ocean-24% of the world’s coral reefs; occur between the coastal lines of India and Srilanka towards north, Thailand, Malaysia and Indonesia to the NE, entrances to the Red Sea and Persian Gulf, Yemen, Oman, Somalia northern Kenya and Madagascar to the west and Australia to the east

• Southeast Asia- 30% of the world’s coral reefs; from Philippines to western Indonesia

• Caribbean- 14% of the world’s coral reefs; includes Caribbean Sea, Gulf of Mexico, South Florida, the Bahamas and North Brazil

• Pacific Ocean Region- 25% of the world’s coral reefs; western Pacific supports richest reef biota, include Micronesia, Palau, Papua New Guinea and Vanuatu

Distribution of coldwater and tropical coral reefs

• Coral reefs are rare along west coast of Americas and Africa- upwelling & strong cold coastal currents

• Seldom found along the coastline of South Asia (eastern tip of India, Bangladesh & Myanmar); northeastern coast of South America

Important coral reefs of the world• Great barrier reef-largest, comprising over 2,900

individual reefs and 900 islands stretching for over 2,600 kilometers off Queensland, Australia

• The Mesoamerican Barrier Reef System—second largest, stretching 1,000 kilometers from Isla Contoy at the tip of the Yucatán Peninsula down to the Bay Islands of Honduras

• The New Caledonia Barrier Reef—second longest double barrier reef, covering 1,500 kilometers

• The Andros, Bahamas Barrier Reef-third largest, following the east coast of Andros Island, Bahamas, between Andros and Nassau

• The Red Sea-includes 6000-year-old fringing reefs located around a 2,000 km coastline

• The Florida Reef Tract-largest continental US reef, extends from Soldier Key, located in Biscayne Bay, to the Dry Tortugas in the Gulf of Mexico

• Pulley Ridge-deepest photosynthetic coral reef, Florida

• The Philippines coral reef area, the second largest in Southeast Asia, is estimated at 26,000 square kilometers and holds an extraordinary diversity of species.

• The Raja Ampat Islands in Indonesia's West Papua province offer the highest known marine diversity

Coral reefs in India

• Palk Bay • The Gulf of Mannar • Andaman and Nicobar Group of Islands. • The Gulf of Kutch • The Lakshadweep Islands

Importance of coral reefs

• Prevent sediments from washing up & damaging the shoreline

• Act as physical barrier; creates healthier, protected coastline habitat

• Sequesters CO₂, create an environment which attract marine biodiversity

• Provides economic benefits

• Harvested for medicinal & jewellery purposes

• Critical habitats essential for the maintenance of biodiversity.

• Tourism (generation of foreign exchange).

• Support fisheries.

References

• Biswas, K.P., Corals of Tropical Oceans, Daya Publishing House 2008, pp 1-13

• www.wikipedia.org• http://www.oceanworld.tamu• http://www.com.univ• http://www.marbef.org• www.perf.org