Productivity depends on the following factors:
- Photosynthetic capacity/Efficiency of the producers.
- Solar energy (Sunlight) → Light intensity, duration, quality
- Availability of nutrients (eg. O2, CO2, minerals)
- Water availability
In case of oceanic ecosystems, productivity is limited by the following factors:
- The amount of light reaching the ocean surface decreases with the increasing depth of the ocean.
- Deficiency of nitrogen in oceans, an important mineral in the growth of plants.
- High salinity in oceans.
- 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.