Question

Why is productivity in oceans lesser than the land?

Answer 1

Productivity depends on the following factors:

1. Photosynthetic capacity/Efficiency of the producers.
2. Solar energy (Sunlight) → Light intensity, duration, quality
3. Availability of nutrients (eg. O₂, CO₂, minerals)
4. Water availability
5. Topography

In case of oceanic ecosystems, productivity is limited by the following factors:

1. The amount of light reaching the ocean surface decreases with the increasing depth of the ocean.
2. Deficiency of nitrogen in oceans, an important mineral in the growth of plants.
3. High salinity in oceans.
4. No substratum to support the plants.

Oceans are very low productivity ecosystem → < 2 tonnes/hectare/year

Although oceans make up 70% of the earth’s surface, it contributes to only 55 billion tonnes out of a total of 170 billion tonnes by the biosphere.