Plankton Extraction
GreenshellTM mussels feed by filtering plankton (small free-floating plants and animals) from the water column. This means mussel farmers don’t need to feed their crop, but it also means farmed mussels depend on the plankton naturally available in the water column.
The amount of plankton uptake by the mussel crop is an essential part of the assessment of effects of a proposed farm because it influences how much food is available to wild species and how much plankton may be removed from an ecosystem.
If there is more than one existing mussel farm in a bay, applications for new farms will often be required to investigate the cumulative effects of further mussel farms on the marine environment.
It is difficult to calculate the actual effects of mussel farming on plankton availability and the flow-on effects to the ecosystem. However, New Zealand researchers use the best available methods to estimate the effects of mussel farming on plankton, both on a site-specific and a cumulative scale.
This includes Geographic Information System (GIS) modelling of the ‘footprint’ of potential phytoplankton uptake, using the percentage of water processed by the mussels as a proxy for plankton depletion. Researchers also measure the actual concentrations of chlorophyll a (which is a proxy for phytoplankton) in the water around mussel farms as a good indicator of phytoplankton levels.
While mussels remove both plant and animal plankton from the water, they also excrete nutrients into the water, which stimulates the growth of plant plankton.
