productivity

[garytse86]

is there any reason that there is a great capacity for high productivity in the water in estuaries?

[iansmith]

Estuaries are nutrient rich. The nutrient richness is due to river runoff and the mixing of salt and fresh water. The nutrient allows microorganism to grow easily and not in a limited fashion. These microorganism becomes food for the zooplankton. Phytoplankton will also grow well. The plankton then become food for the bigger fauna such as fish.