Ecopol Project - Portland State University

Dead zones and aquaculture 

Aquaculture, better known as fish farming, is another source of increasing oceanic nutrient pollution. Since 1985, aquaculture production mass has increased worldwide by 600% from 8 million to almost 50 million tons per year. These farms consist of marine life, such as fish or shrimp, concentrated together in nets or cages housed near the shore, often within enclosed bays, generating highly condensed pollutants like nitrogen and phosphorus from excess food and excrement. Improper development and management of these oceanic farms can have severe negative impacts on the surrounding waters and organisms.
This problem wraps full circle as the next generations of farmed animals struggle to survive in the continuously declining oxygen levels of the nearby waters. One proposed idea to help restore more ordinary water conditions is through the utilization of bivalves. Bivalves, such as mussels, could be strategically placed to feed on the increased phytoplankton blooms that result from the nutrient enriched waters beneath the fish farms. As a consequence, bivalves could reduce the overall amount of excess decaying biomass that causes the low oxygen levels.

Image credit: World Resources Institue: Michael L. Webe SeaWeb Aquaculture Clearing House