Why Is Productivity Low in Tropical Regions

Multiple Choice

Why is productivity low in tropical regions?

A) because the low density of the water makes it hard for plankton to float near the surface
B) because there is too much sunlight
C) because the deep waters are too warm to maintain a healthy biomass
D) because the thermocline acts as a barrier to the mixing of surface and deep waters
E) All of the above are problems.