Corals reproduce and grow through a complex combination of asexual and sexual reproduction
Corals start life as single embryos drifting in the current
The embryo attaches to the sea floor becoming an individual coral polyp
This polyp reproduces asexually through a process called budding or fission
This process is repeated over and over
with each polyp laying down a cup of limestone as it moves up to a new layer
If budding were the only means of reproduction
corals would not be able to adapt to changing conditions
So they must reproduce sexually as well
Sexual reproduction produces new combinations of genetic material
and therefore enables corals to evolve
During spring nights whole colonies climax simultaneously
releasing bundles of eggs and sperm into the water column
By spawning together during the night hours
the corals give their sexual packages the best chance of being fertilised
Once released these sexual packages combine with those of other colonies
to form the free-swimming planktonic stage of coral, the planula
these larval messengers may stay as part of the plankton for days or even months
as they drift in search of a new home
the larvae eventually settles down and the cycle starts again