Table 3. Model state variables and main terms (see also Fig. 4)


State variable(s) and units subject to ex-change external inputs & outputs local gains local losses effects on Reference
chlorophyll
mg m-3
yes light and nutrient controlled growth mesozoo-plankton and benthic grazing itself(-), via transparency; nutrients (-); mussels (+) dCSTT model (Tett et al. 2003, Laurent et al 2006)
nutrients (N, P, Si)
mmol m-3
yes recycling from grazing uptake by phytoplankton chlorophyll (+) dCSTT model, as above
POM
mg m-3
yes mussel pseudo-faeces feeding by mussels; sinking mussels (+)
AFC(s)
g m-3 [ as mg/L]
yes from yachts in marinas none none chlorophyll (-) MAMPEC (van Hattum et al. 2002)
individual mussel biomass
mg C
no initial biomass at seeding feeding on algal C (from chlorophyll) and POM C respiration chlorophyll (-); POM (-); farm revenue (+) Grant & Bacher 1998
mussel numbers
(c x lines)
no seeding (+), harvest (-) natural mortality as above, mussel biomass (effect = numbers x biomass)
mussel farm revenue no selling harvested mussels (unit price depends on biomass) pay to employees; taxation; replacing depreciated capital; cost of seed [employment in local community]§
marina revenue no renting moorings (to yachts) pay to employees; taxation; replacing depreciated capital AFCs release (+)
[employment in local community]§
In each sector the simulated number of employees was set by the size of the enterprise. Mussel farms had 1 full-time employee per 4 lines, and 12 lines were simulated in loch Fyne. Marinas had 10 full-time employees per 250 berths, plus seasonal employees up to 10 when the berths were full.
A line is a mussel farm unit, comprising a line of moored buoys, each supporting a rope containing c mussels when seeded at the start of year 1; simulated harvest took place in year 2.
§Employment in the local community by the enterprises: we used the annual total of wages paid to people directly employed as a proxy for social benefit;