Ecasa Toolbox

Public Environment Management: Planning considerations

Aquaculture can impact on the environment on 3 scales. 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. On the regional scale, the spread of aquaculture may interact with other human activities to bring about extensive disturbance of the sea-bed and eutrophication. Three main EU directives must be taken into account: the Shellfish Directive (maintainance of water quality where shellfish are exploited); the Species & Habitats Directive (protection of certain species and habitats); and the Water Framework Directive (maintainance of good ecological and water quality).

Because of the potential for conflicts amongst different uses of coastal waters, it is desirable to develope plans that identify zone C scale regions that are most suitable for aquaculture of various sorts. Within these regions will be water bodies, each of which has a certain capacity to assimilate waste, or to carry (support) a harvest of filter-feeding shellfish, without significant effects on ecological quality. Ecologically sustainable aquaculture in coastal waters can be ensured by managing developments to stay within these capacities. See: Management for sustainability.

ECASA did not study regional-scale sustainability in any detail, but we have tested models that can be used to estimate assimilative capacity or carrying capacity on water body (zone B) scales. The following models will be useful for planning on this scale. All need information on 'boundary conditions'.

EnvironmentScaleSpeciesRelevant CapacityModel alphabetical order
See also: Choosing a model.
Regions of Restricted Exchange (Fjords, sea-lochs, voes, rias, barrier lagoons)B: water-bodymussels, oystersCarryingEcoWin + ShellSIM
Needs information on water movements.
Regions of Restricted Exchange (Fjords, sea-lochs and voes)B: water-bodysalmon, codAssimilativeFjordEnv
Both include 3-layer hydrodynamic model.
Open meso- or macro- tidal watersB: water-bodymussels, scallopsCarryingLonglines
Needs information on water movements