Give scientific reasons: Algae are the most important primary producers.

(N/A) $\rightarrow$ At least half of the total carbon dioxide fixation on the earth is carried out by algae through photosynthesis.
Being photosynthetic,they increase the level of dissolved oxygen in their immediate environment.
They form the basis of food cycles for aquatic animals.
Many marine algae are used as food,and they also produce commercial products such as Algin and Carrageen.