In aquatic ecosystems, the limiting factor for the productivity is_______.

Sunlight

Limiting factors are environmental influences that constrain the productivity of organisms, populations, or communities and thereby prevent them from achieving their full biological potential which could be realized under optimal conditions. So if the amount of light entering in the pond decreases it will affect the productivity of the ponds as the phytoplankton and other aquatic plants would not be able to perform the photosynthesis and ultimately the productivity of pond will decrease.