| ... | ... | @@ -39,72 +39,4 @@ The shellfish populations are controlled by a variable mortality (MortShellfish) |
|
|
|
[top](NPZ model)
|
|
|
|
|
|
|
|
[top](NPZ model)
|
|
|
|
# Shellfish scope for growth
|
|
|
|
Processes related to the physiology of the shellfish are described by a scope for growth model.
|
|
|
|
|
|
|
|
## Clearance
|
|
|
|
For each shellfish species (i) the individual clearance rate (〖CR〗_i, l h-1) is calculated using the allometric relation:
|
|
|
|
〖CR〗_i=a_i∙〖W_i〗^(b_i )
|
|
|
|
Where W_i is the average weight of the shellfish species i (g AFDW), and a_i and b_i are species-specific coefficients. The total clearance rate (〖Clearance〗_i) [m3 m-2 d-1] for species i is calculated by
|
|
|
|
〖Clearance〗_i=〖CR〗_i∙N_i∙24/1000
|
|
|
|
With N_i is the number of individuals per m2 of species i. The factor 24/1000 is to convert from l h-1 to m3 d-1.
|
|
|
|
The total clearance rate is the sum of the clearance rates of all shellfish species.
|
|
|
|
Clearance=〖Clearance〗_MUS+〖Clearance〗_OYS+〖Clearance〗_COC
|
|
|
|
|
|
|
|
## GrazingPhy
|
|
|
|
The grazing rate of the shellfish on phytoplankton (〖Grazing〗_(Phy,i)) [mmol N m-2 d-1] is calculated from the clearance rate (〖Clearance〗_i) multiplied by the phytoplankton biomass.
|
|
|
|
〖Grazing〗_(Phy,i)=〖Clearance〗_i∙Phyto
|
|
|
|
|
|
|
|
## GrazingZoo
|
|
|
|
The grazing rate of the shellfish on zooplankton (〖Grazing〗_Zoo) [mmol N m-2 d-1] is calculated from the clearance rate (Clearance) multiplied by the zooplankton biomass.
|
|
|
|
〖Grazing〗_(Zoo,i)=〖Clearance〗_i∙Zoo
|
|
|
|
|
|
|
|
## GrazingDet
|
|
|
|
The grazing rate of the shellfish on detritus (〖Grazing〗_Det) [mmol N m-2 d-1] is calculated from the clearance rate (Clearance) multiplied by the detritus biomass.
|
|
|
|
〖Grazing〗_(Det,i)=〖Clearance〗_i∙Det
|
|
|
|
|
|
|
|
## Ingestion
|
|
|
|
The total concentration of food for the shellfish [mgC m-3] is the sum of phytoplankton, zooplankton and detritus in units of carbon. This is calculated from Phyto, Zoo and Det, respectively, from the molecular weight of C and assuming a fixed C/N ratio. The total food concentrations in units of C is calculated from:
|
|
|
|
FoodC=PhyC+ZooC+DetC
|
|
|
|
Ingestion rate [mg C d-1] for each inidivdual of species i is a function of the size of the shellfish, the food concentration described by a Holling type-II functional response.
|
|
|
|
〖Ingestion〗_i=I_(m,i)∙〖W_i〗^(b_(m,i) )∙FoodCk_i+FoodC∙Tfac
|
|
|
|
Where I_(m,i) is the reference ingestion rate for shellfish i, W_i is the mean individual weight [mg AFDW] and b_(m,i) is the allometric exponent for ingestion. k_i is the half-saturation coefficient for shellfish i [mg C m-3],
|
|
|
|
|
|
|
|
## Assimilation
|
|
|
|
A fraction of the ingestion is used for assimilation [mg C d-1]:
|
|
|
|
〖Assimilation〗_i=ε_i∙〖Ingestion〗_i
|
|
|
|
With ε_i is the dimensionless species specific feeding efficiency.
|
|
|
|
ε_i=((ε_(i,PhyZoo)∙(PhyC+ZooC)+ε_(i,Det)∙μ_i∙DetC)/((PhyC+ZooC)+μ_i∙DetC))
|
|
|
|
ε_(i,PhyZoo) is the dimensionless phytoplankton and zooplankton assimilation efficiency for shellfish species i and μ_i is the dimensionless feeding preference coefficient for species i. PhyC, ZooC and DetC are phytoplankton, zooplankton and detritus concentration in units of gC m-3.
|
|
|
|
|
|
|
|
## Respiration
|
|
|
|
Respiration rate is the CO2 production by an individual organism [mg C d-1] and is composed of basal respiration (R_(B,i)) and costs for growth (R_(G,i)).
|
|
|
|
〖Respiration〗_i=R_(B,i)+ R_(G,i)
|
|
|
|
The costs for growth is assumed to be a fixed fraction of the assimilation rate:
|
|
|
|
R_(G,i)=σ_i∙〖Assimilation〗_i
|
|
|
|
Basal respiration is a function of the size of the animal and increased with the water temperature:
|
|
|
|
R_(B,i)=β_(RS,i)∙〖W_i〗^(b_(m,i) )∙T_fac
|
|
|
|
β_(RS,i) is the standard respiration rate for species i [d-1] and b_(m,i) is a coefficient.
|
|
|
|
Respiration rate is expressed in units of mg C d-1.
|
|
|
|
|
|
|
|
## DINprod
|
|
|
|
〖DINprod〗_i is the respiration rate of the total shellfish stock of a particular species within the compartment in units of mmol N m-2 d-1 and is calculated from the respiration rate of an individual organism.
|
|
|
|
〖DINprod〗_i=(〖Respiration〗_i∙N_i)/(C⁄N∙M_c )
|
|
|
|
Where N_i is the number of shellfish species i per m2, C⁄N is the C/N ratio of the food and M_c is the molar weight for carbon (g mole-1).
|
|
|
|
|
|
|
|
## Growth
|
|
|
|
Growth [mmol N m-2 d-1] of the total stock is calculated from the difference between the individual assimilation rate [mg C d-1] and respiration rate [mg C d-1]. The difference is multiplied by the average density of the species within the compartment (N_i) [# m-2] and corrected for the C/N ratio and the molar weight of C to obtain growth in units of mmol N m-2 d-1.
|
|
|
|
〖Growth〗_i=(〖Assimilation〗_i-〖Respiration〗_i )∙(N_i/(C⁄N∙M_c ))
|
|
|
|
|
|
|
|
## Faeces
|
|
|
|
Faeces production is of the total stock [mmol N m-2 d-1] is calculated from the difference between individual ingestion rate [mg C d-1] and assimilation rate [mg C d-1]. The difference is multiplied by the average density of the species within the compartment (N_i) [# m-2] and corrected for the C/N ratio and the molar weight of C to obtain faeces production in units of mmol N m-2 d-1.
|
|
|
|
〖Faeces〗_i=(〖Ingestion〗_i-〖Assimilation〗_i )∙(N_i/(C⁄N∙M_c ))
|
|
|
|
|
|
|
|
## Pseudofaeces
|
|
|
|
Pseudofaeces production of the total stock is calculated from the difference between individual filtration rate [mg C d-1] and ingestion rate [mg C d-1]. The difference is multiplied by the average density of the species within the compartment (N_i) [# m-2] and corrected for the C/N ratio and the molar weight of C to obtain pseudofaeces production in units of mmol N m-2 d-1.
|
|
|
|
〖Pseudo_faeces〗_i=(〖Filtration〗_i-〖Ingestion〗_i )∙(N_i/(C⁄N∙M_c ))
|
|
|
|
Where individual filtration rate [mg C d-1] is calculated from the total clearance rate [m3 m-2 d-1] and the amount of food [mgC m-3]
|
|
|
|
〖Filtration〗_i=(〖Clearance〗_i∙FoodC)/N_i
|
|
|
|
|
|
|
|
|
|
|
|
[top](NPZ model) |
