Oyster reefs can remove over 1,000kg of nitrogen per hectare per year.

Oyster reefs mitigate Eutrophication, the leading cause of coastal dead zones worldwide.

How it works:

Biological Nutrient Removal

Through their filter-feeding activity, oysters extract suspended organic material - including nitrogen-rich phytoplankton - from the water. These nutrients are either assimilated into oyster tissue and shell, deposited in biodeposits (pseudofaeces and faeces), or transformed into nitrogen gas via microbial processes such as denitrification.

Biodeposits settle into reef sediments, where bacteria convert reactive nitrogen into inert nitrogen gas (N₂), effectively removing it from the ecosystem.

This makes oyster reefs a powerful nature-based tool to combat nutrient pollution from urban runoff, agriculture and sewage discharge.

Benefits at a glance:

• Nitrogen Removal: Filters and transforms reactive nitrogen

• Phosphorus Reduction: Sequesters phosphorus in shell and tissue

• Eutrophication Mitigation: Prevents algal blooms and oxygen depletion

• Microbial Cycling Support: Promotes denitrification via reef sediments

• Ecosystem Health: Helps maintain water quality and biodiversity

Balancing the Nutrient Budget

In healthy oceans, oysters act like kidneys — helping to maintain nutrient balance and water quality. But when reefs are lost, excess nitrogen and phosphorus can fuel eutrophication, leading to low-oxygen zones and biodiversity collapse.