Ecologically, shellfish provide two distinct ecosystem services. Primarily, they are a food source for humans and other animals in the estuarine ecosystem. Shellfish provide a cost-effective, high quality protein-based food for humans. Because shellfish are filter feeders, eating low on the trophic level, they could be considered a more energy efficient food source.
The second ecosystem service is their filter feeding mechanism. Bivalves have the ability to clean water through the filtration and consumption of solid particulate matter, primarily phytoplankton (microscopic algae.) This service is becoming increasingly valuable as coastal areas continue to develop because runoff of fertilizers and nonpoint source pollution become more pronounced. Fertilizers usually contain nitrogen and phosphorous, which create algal blooms in the water. An abundance of algae depletes dissolved oxygen in the water, a process known as eutrophication. Eutrophication disrupts the entire ecosystem and can deplete populations of a variety of valuable species.
Accurate knowledge of bivalve filter feeding ecology is important for selection of shellfish farm location and designing the layout of the farm, calculating yield and carrying capacity, and for assessing ecosystem services and impacts. When depending on the filtering service for water quality, one must take into account the variability of filter feeding. Filter feeding rates vary according to spatial and temporal conditions. As a nonlinear function, this has implications for predicting the amount of pollution that shellfish can filter. As with any organism, there needs to be a balance between the food source and the consumer. Overloading the ecosystem with runoff waste would lead to eutrophication regardless of the presence of shellfish. By contrast, planting oysters or other shellfish above their carrying capacity – without enough food—would affect the yield of the farm.