World expert reveals aquarium secrets

Coral reefs; the jewels in the sea

CORAL REEFS; THE JEWELS IN THE SEA

Sangeeta Roy and Rajesh Kumar Mohapatra

Utkal University, Bhubaneswar, Odisha-751004

INTRODUCTION

            Corals areCalcareous skeleton or fused skeletons of colonial coelenterates or the skeleton together with the animals (Polyps) which secrete it. Coral colonies grow continuously in size by budding of polyps and form extensive masses known as Coral Reef. A coral reef is a mound of lime stone, which is formed chiefly of CaCO3 secreted by Coral polyps, that serves as a home to animals and plants.

CLASSIFICATION

            Coral forming polyps belong to the phylum Coelenterate and class Anthozoa. Class Anthozoa includes three sub-classes that are Octocorallia, Hexacorallia and Tabulata.

Subclass I – Octocorallia (Order: Stolonifera,Telestacea,Alcyonacea,Coenothecalia, Gorgonacea, Pennatulacea)

Subclass II – Hexacorallia (Zoanthidea, Actiniaria, Ceriantharia, Antipatharia, Madreporaria)

Subclass III – Tabulata (Extinct colonial anthozoans) 

TYPES OF REEFS

            Naturalist Charles Darwin’s theory of Coral formation is widely accepted. This theory recognizes three types of reefs.

Fringing reef: Fringing reefs border shore lines of continents and islands in tropical seas. Fringing reefs are commonly found in the south pacific Hawaiian Islands and parts of the Caribbean.

Barrier reef: Barrier reef occurs farther offshore. Barrier reefs form when land masses sink and fringing reefs become separated from shorelines by wide channels. The Great Barrier Reef off northern Australia in the Indo-pacific is the largest barrier reef in the world. Atoll: If the land mass is a small island, it may essentially disappear below the ocean surface and the reef becomes an atoll. Atolls are reefs that surround a central lagoon. Atolls commonly occur in the Indo-pacific.

DISTRIBUTION

            Reef building corals are scattered throughout the tropical and subtropical western Atlantic and Indo-pacific oceans, generally within 30 degrees N and 30 degrees S latitudes. Western Atlantic reefs include these areas – Bermuda, Bahamas, Caribbean islands, Belize, Florida and the Gulf of Mexico. The Indo-pacific ocean region extends from the Red Sea and the Persian Gulf through the India and Pacific oceans to the Western Coast of Panama.

CONDITION FOR THE FORMATION OF CORAL REEF

            Reef building corals are generally found at depths of less than 150ft. (46m) where sun-light penetrates. Because reef Building Corals have a symbiotic relationship with a type of microscopic algae, sunlight is necessary for these corals to thrive and grow. Reef tends to grow faster in clean water. Clean water allows light to reach the symbiotic algae living with in the coral polyp’s tissue. Reef building corals required warm ocean temperatures (68 to 82OF or 20 to 28OC). Reef development is more abundant in area that is subject to strong wave action. Waves carry food, nutrients and oxygen to the reef, distribute coral larvae and prevent sediment from settling on the coral reef. Precipitation of calcium from the water is necessary to form a coral polyp’s skeleton, this precipitation occurs when water temperature and salinity are high and carbon dioxide concentrations are low.

THE CORAL REEF ECOSYSTEM

            The coral reef ecosystem is a diverse collection of species that interact with each other and the physical environment. The sun is the initial source of energy for this ecosystem. Reef building corals have a symbiotic relationship with zooxanthellae, microscopic algae that live with coral polyps tissues. Through photosynthesis zooxanthellae convert carbon dioxide and water into oxygen and carbohydrates. The coral polyps use carbohydrates as a nutrient and oxygen for respiration and in turn return carbon dioxide to the zooxanthellae. The reef provides shelter for many animals, including sponges, sea anemones, Bryozoans worms, sea stars, sea cucumbers, sea urchins, crustaceans, molluscs, variety of fishes, sea turtles, sea snakes. Reefs are also formed in deep water. The deep water reefs are formed by deep water corals.

DEEP WATER CORALS

            Deep water corals are found beyond the reach of sunlight and are adapted to the dark environment. Deep water coral polyps do not contain the symbiotic algae. Deep water coral rely on catching passing food in the water column. As a result corals grow very slowly. Deep water coral colonies tend to be found in areas where there are strong water currents, which supply food and remove sediments. Three main groups of corals make up deep watercoral communities: 1.Hard (Stony) corals of the order scleractinia, 2.Black and horny corals of the order Antipatharia, 3.And soft corals of the order Alcyonacea, which includes the gorgonians

IMPORTANCE OF CORALS

            Corals remove and recycle carbon dioxide. Excessive amounts of Co2 gas contribute to global warming and reef help to reduce it. Reefs protect coast from strong currents and waves. Reefs provide resources for fisheries. Coral reef provides important medicines including anti-cancer drugs. Reefs provide protection and shelter to many marine animals.

THREAT TO CORAL REEFS

Water Pollution: Reefs are harmed when animal wastes, industrial wastes or fertilizers are dumped into the ocean; these pollutants increase the level of nitrogen, causing an overgrowth of algae, which harm the reefs by blocking off sunlight that polyps need to survive. Sedimentation: Construction along coasts, mining and farming along coastal rivers can lead to soil erosion. Silt from eroded soil end up in the ocean and cover coral reefs. This deprives corals from the light which they need to survive.

Destructive Fishing Practices: Destructive fishing practices are applied for catching fishes like cyanide fishing and blast fishing, which kill coral polyps, the symbiotic algae and other small organisms.  

Coral Mining: Mining also destroys coral, coral pieces are removed for use as bricks or road fill or sand and limestone from coral reefs are made into cement for new buildings. Corals are also sold as coral jewellery.

Careless Tourism: Careless boating, driving snorkeling and fishing can also damage coral reefs. Corals are also harmed when people drop anchors on them. Also, the disposal of sewage from tourist resorts contributes to coral reef degradation.

Ocean Warming and Coral bleaching: Global warming is caused by the accumulation of CO2 and other heat trapping gasses in the atmosphere. These gases act as a blanket, preventing the neat of the sun to escape through our atmosphere, this is causing sea surface temperature to rise, increased water temperatures, can cause mass coral bleaching. This occurs when coral polyps stressed by heat expel the algae that live within them, algae are normally responsible for the colour of coral, so when they are expelled, the coral appears bleached or white. The symbiotic algae zooxanthellae are responsible for the colour of the coral belongs to the phylum Dinoflagellata. Also natural pigments in the coral tissue produce a range of colours including white, red, orange, green, blue and purple.

Carbon Dioxide: Increased amounts of carbon dioxide are dissolving into the water because in the past few decades, the amount of carbon dioxide in the air has increased as a result coral in waters with large amounts of carbon dioxide form weaker skeletons, making them more vulnerable to damage from waves.

About the Author

SANGEETA ROY AND RAJESH KUMAR MOHAPATRA

UTKAL UNIVERSITY, BHUBANESWAR, ODISHA-751004

rajesh.wildlife@gmai.com

Coral reef wonderland – Wild Indonesia – BBC