Question

Which factor primarily limits primary productivity in marine ecosystems?

• A. Light
• B. Nitrogen and phosphorus availability
• C. Oxygen
• D. Temperature

Hint:

In marine ecosystems, \[ \boxed{ \text{Nitrogen and Phosphorus} \rightarrow \text{Major limiting nutrients} } \]

Answer 1

The Correct Option is B

Step 1: Recall what phytoplankton need to grow.
Sunlight is rarely scarce at the ocean surface, so the real bottleneck for photosynthetic organisms is having enough raw nutrients to build new cells.
Step 2: Identify which nutrients run short.
Nitrogen and phosphorus are needed in relatively large amounts for proteins, DNA and cell membranes, and in most open ocean waters these two are in short supply.
Step 3: See the effect on productivity.
When nitrogen and phosphorus levels drop, phytoplankton growth slows even if light and carbon dioxide are plentiful, so these nutrients become the controlling factor.
\[ \boxed{\text{Nitrogen and phosphorus availability}} \]