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Even though coral reefs occupy less than one percent of the ocean floor,these dense ecosystems are home to more than twenty-five percent of marine life.Many fish use corals as shelters for sleeping and to hide from large predators between their trips foraging for seaweed.As the primary food source for many of the reef fish and invertebrates,seaweed is vital to this ecosystem.But in high densities, seaweed can become problematic,and even lethal to corals.

But coal also releases pollutants into the air,like sulfur dioxide,nitrogen oxides,soot,and toxic metals, like mercury.These cause environmental damage,like acid rain,and serious health problems.In fact, in 1952, coal burning caused such heavy smog in London that pedestrians couldn't even see their feet,and thousands of people died from ill health.Since then, many countries have deployed technology to remove most of these pollutants before they reach the air.

Massive coral reefs begin with tiny coral larvae,which settle on the seafloor hard surfaces and metamorphasize into coral polyps.Over time, these polyps generate rock-like skeletons made of calcium carbonate.Together, colonies of polyps produce large three-dimensional structures,which form the basis of an underwater metropolis.These coral complexes are full of nooks and crannies that house and protect countless life forms.

As the sun rises over a quiet coral reef, one animal breaks the morning silence.Named for their vibrant scales and beak-like teeth,these parrotfish are devouring a particularly crunchy breakfast: rocks.It may not be immediately clear why any creature would take bites out of the seafloor.But the diet of these flashy foragers actually plays a key role in defending the coral reef complex ecosystem.