Question

question 3 (1 point)
benthic and encrusting algae on coral reefs____________________.
generally constitute most of the biomass of primary producers in the reef
ecosystem.
are found in only limited numbers because of the low availability of nutrients.
are responsible for building much of the reef structure with their hard parts.
cooperate in an association with zooxanthellae to rapidly recycle nutrients.
the first and third answers are correct.

Explanation:

Benthic and encrusting algae are key primary producers in coral reefs, making up most primary producer biomass. Encrusting algae (e.g., coralline algae) have hard calcium carbonate structures that contribute to reef building. Option 1 states they are the main primary producer biomass (correct), option 3 states they build reef structure with hard parts (correct). Other options are wrong: they are abundant (not limited), reef structure building is by encrusting algae (not just zooxanthellae), and their cooperation with zooxanthellae is not the reason for nutrient recycling here.

Answer:

E. the first and third answers are correct.