Answer: coral reef
Well, you may ask what is a coral reef?
Coral is a ridge of rock in the sea formed by the growth and deposit of coral for explaining:
"the small island is enclosed in the middle of the coral reef"
Why is it so low this is why.
Coral reefs are under relentless stress from myriad global and local issues, including climate change, declining water quality, overfishing, pollution, and unsustainable coastal development.