Find out what do the terms ‘algal bloom’ and ‘red-tides’ signify

Explanation

Algal bloom' : When colour of water changes due to profuse growth of coloured phytoplanktons, it is called algal bloom.
'Red tides' : Redness of the red sea is due to luxuriant growth of Trichodesmium erythrium, a member of cynaobacteria (blue green algae).