SPEAKER 1: Let's take a closer look at coral reefs and the small creatures that build them. The coral reefs are considered the largest living structures on the planet. They are the accumulation of millions of colonies of tiny individual organisms called coral polyps.
Corals are colonial invertebrates. A colony of coral is made up of interconnected individual polyps, which share nutrients between each other. Coral polyps have one body opening, which serves as both the mouth and the anus. This is surrounded by stinging tentacles.
Despite this seemingly simple body plan, corals have comparably advanced nervous and muscular systems and can detect and react to a wide variety of stimuli, including chemicals, touch, and light.
These tiny creatures are micro-carnivores. They can use their tentacles to capture zooplankton prey. However, most coral also get extra nutrients from single-celled algae living within their tissues.
These zooxanthellae are an interesting example of symbiosis between plants and animals, that is actually an Achilles heel in warming oceans. The coral polyp provides the zooxanthellae with a protected habitat and nutrients they need to carry out photosynthesis.
The zooxanthellae, in turn, provide the coral polyps with an energy source and organic carbon. Without the zooxanthellae, these small animals would not have enough energy to build the vast calcified coral reef structure.
Zooxanthellae also give corals their colors. But here is the Achilles heel-- when coral are heat stressed, they expel their zooxanthellae and turn white, a process called coral bleaching. Corals can recover from short-term bleaching events. But if they remain in a bleached state for too long-- such as for weeks and weeks on end-- they can die.
You may be asking yourself, how do such tiny organisms form structures as massive as the Great Barrier Reef in Australia? Corals form reef structures as individual polyps grow, and build small calcium carbonate skeletons around themselves. These small skeletons accumulate over thousands of years to form the enormous reefs found in tropical oceans today.
Geographically, corals are generally found in warm, clear waters that are nearly void of nutrients. Though reflex structures have existed on earth for nearly 200 million years, these conditions make them fragile ecosystems, which are sensitive to changes in sea level, ocean temperature, and ocean circulation patterns.
Reefs are also affected by other events, such as the addition of nutrients, and sediments from runoff, storms, and human activity. In any combination, these detrimental factors can threaten coral ecosystems and make them more susceptible to damage and disease.
We have observed decline in reefs occurring at an alarming rate in the last three decades. In the next section, we take a closer look at the potential causes and consequences of coral reef decline.
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Over the last 20 years we have observed coral reefs declining at an alarming rate. What is causing this catastrophe and what can be done to prevent further damage?
This study room examines the causes of coral reef decline, including increasing ocean temperatures, overfishing, and runoff from coastal areas. The room describes research on coral disease and how coral organisms resist disease. The research is being conducted by graduate students, undergraduate students, and researchers, who describe their work in their own words.
This video is part 2 of 10 in the Coral Reef Sustainability series.