Question

Why can algae and cyanobacteria be considered indicators of productivity as well as of pollution

Answer 1

Algae and Cyanobacteria could mean life is flourishing and is a good food source for some fish in moderation- but if there's a lot of fertilizer runoff, they can grow too quickly and be counterproductive for the environment

Answer 2

They can be both positive and negative to the environment.

Step-by-step explanation:

Algae and cyanobacteria are used both in industrialized process of biotechnology and the cyanobacteria in a certain degree can help the algae flourish, upto a certan concentration, once we are past that point the cyanobacteria is considered pollution and wont help the algae reproduce anymore.