Using shellfish to clean up excess nutrients and pollution from water bodies

Shellfish aquaculture is gaining acceptance as a method to remove excess nutrients and contaminants from coastal and estuarine waters, says a recent report.

Excess nutrients such as nitrogen that end up in rivers and streams as the result of human activities can cause algal blooms, loss of seagrass and low oxygen levels, which can lead to large numbers of fish and other organisms dying.

According to the American Chemical Society, many studies have examined how to prevent this runoff, but not much attention has been paid to removing the nutrients from the water.

Geukensia demissa, known as the ribbed mussel, is one type of shellfish proposed for these nutrient removal programs. This mussel lives in various habitats and can filter bacteria, microalgae, and detritus containing nutrients and contaminants. In addition, this shellfish is not for sale on the commercial market, so these mussels aren’t directly consumed by humans.

To see whether G. demissa could clean up dirty water in an urban environment, a raft stocked with local ribbed mussels was deployed in late June 2011 in an estuary at an industrial setting near New York City. The raft is a floating platform with beams and underwater ropes to which the mussels attach. The next spring, the researchers harvested the raft and studied the mussels.

Overall, the mussels were healthy, and their tissues had high amounts of a local nitrogen isotope, indicating that they removed nitrogen from the water. Based on their study, the group estimates that a fully stocked raft would clean an average of 11,356 m³ of water and remove about 159 kg of particulate matter, like dust and soot, daily. In addition, when the mussels were harvested, 62.6 kg of nitrogen would be sequestered in mussel tissue and shell.

The report, titled “Cultivation of the Ribbed Mussel (Geukensia demissa) for Nutrient Bioextraction in an Urban Estuary” was published in Environmental Science & Technology on November 8, 2017.