Public Environment Management: Monitoring aquacultural impacts

On the scale of a farm, finfish and bivalve shellfish consume oxygen and release ammonia (and phosphate); their particulate waste can perturb, and in the worst case destroy, sea-bed communities. Filter-feeding shellfish remove phytoplankton. On the scale of a waterbody, nutrients released into the water can stimulate increased growth of phytoplankton or seaweed, with consequences such as harmful algal blooms and deep water deoxygenation. Consequential changes in transparency can impact on seaweed or seagrass distributions. In order to ensure sustainable use of the natural environment, these effects must be kept within tolerable levels - i.e. within the assimilative capacity of the site or water body. For some variables (such as oxygen concentration at the farm), it is in the interests of the farmer to do this. Other impacts need to be monitored by the public authorities. Below, we suggest indicators that can be used to monitor the effects of aquaculture on environmental quality.