Ecosystems

The ocean’s net primary productivity is approximately 55 billion tons (gigatons) of organic matter annually.
Though oceans cover ~70% of Earth's surface, their productivity per unit area is less than terrestrial ecosystems, but total contribution is large due to vast area.

Step 1: Gross primary productivity (GPP) is the total energy fixed by autotrophs.
Step 2: Net primary productivity (NPP) = GPP - Respiration (R). So, NPP is always less than GPP.
Step 3: Reason talks about consumers, but Assertion is about producers.
Step 4: While Reason is a correct definition, it does not support or explain the Assertion—it refers to a different concept.