Question

If there is no algae, there would be no fish in the sea. comment

Answer 1

If there will be no algae, no fishes would be present in the seas because the small or big fishes living in the seas feeds generally on algae floating in the water or present at bottom of the sea waters. If the algae will not be present then all fishes living in the sea will die.

Answer 2

Algae produce O2 as a result of photosynthesis. This oxygen is utilized by the fishes in the sea for  carrying out respiration. If there were no algae, no oxygen would have been produced. Thus, fishes might  have died.