Marine Biology

I. Introduction

Introduction

       Coral reefs are the most luxuriant and complex of all benthic communities; and they are found all around the world. The term "coral reef" generally refers to a marine ecosystem in which the main organisms are corals that house algal symbionts within their tissues. These form the largest biogenic reefs in the world. Over a vast region (millions of square miles) of the tropics, the shallow inshore waters are dominated by the formation of coral reefs, and they are often used to define the limits of the tropical marine environment. These are the largest living structures (biogenic reef) on earth, and there are over 4,000 species of reef fish, making coral reefs the home for one fourth of all the fish species found on the earth. 

              Coral reefs are often referred to as ‘tropical rainforests of the sea’ since they are one of the most diverse, productive, and beautiful marine ecosystems in the world.

Coral reefs resemble tropical rainforests in the following ways:

·         Both thrive under nutrient-poor conditions (where nutrients are largely tied up in living matter), yet support rich communities through incredibly efficient recycling processes.

·         Both exhibit very high levels of species diversity.

·         Coral reefs are noted for some of the highest levels of total (gross) productivity on earth. The net primary productivity of coral reefs is approximately 2,500 grams of carbon per square meter per year, compared to 2,200 grams of carbon per square meter per year for tropical forests and only 125 grams of carbon per square meter per year in the open ocean.

              The extraordinary diversity of reefs makes them biologically important and, like rainforests, they have provided valuable scientific insights into the nature of underwater ecology. It 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. They are considered to be one of the most sensitive to any change. When they are environmentally stressed they lose much of the algae that give them the color along with other pigments. When this happens the corals appear white in colour and are referred to as bleached.

          A coral colony may consist of thousands of polyps. Polyps are typically carnivorous, feeding on small particles floating in the water. Corals reproduce both sexually and asexually. An entire colony many meters in diameter can start out as a single polyp. On a few nights of each year, many of the corals on the reef reproduce in an event called mass spawning. Tens to hundreds of species of corals release their eggs and sperm into the water on the same night. The eggs float to the ocean’s surface where they can be fertilized, forming new coral larvae called planulae. The coral planulae swim in the ocean for several days to weeks until they settle on the reef bottom and grow into new corals. Corals can also reproduce asexually by budding. During budding the coral polyp will divide to make a nearly identical copy of itself that will remain attached to the parent polyp. A coral colony will form after repeated rounds of budding and can grow to contain hundreds and even thousands of polyps. As new polyps form they overgrow older polyps that die and add their calcium carbonate skeleton to the foundation of the reef.