The sad topic of coral bleaching. This pic is of the Great Barrier Reef in Queensland, Australia. The reef has become harmed by coral bleaching over the last 24 years.
How is it caused?
Coral bleaching is caused when the water heats up. Coral has a symbiotic relationship with a microscopic algae called zooxanthellae which gives the coral its colour. When coral is stressed from changes in conditions such as temperature, light or nutrients, it releases the algae that gives the coral its colour.
The algae is also the coral's food, so the coral may die. Corals can survive bleaching, because they also eat zooplankton which are actually the smallest animal on earth.
Eating
You may be wondering 'how do corals eat when they release algae?' Well, at night coral polyps (explained later,) come out of their skeletons, reaching their long, stinging tentacles out to capture the floating critters. Prey are pulled into the polyps mouths and digested in their stomachs.
Polyps
Coral polyps are invertebrates the size of a pinhead. Each polyps has a sac-like body with a mouth that is surrounded by stinging tentacles.
What can we do to prevent this happening?