Mechanisms relating the ocean-scale distribution of Calanus finmarchicus to environmental heterogeneityDouglas Speirs
Jo King:
Acknowledgments: Bill Gurney (Strathclyde) Mike Heath (FRS Aberdeen) Simon Wood (Glasgow University) SOC, PML, SAHFOS
Why Calanus finmarchicus ?2 mm
Widespread & Abundant
Links to Fish Stocks
Extensively studied
Continuous Plankton Recorder Surveys
Calanus abundance and Circulation
The life-cycle of Calanus finmarchicusOmnivorous, but feeds mainly on phytoplankton.
x1000 difference in body weight between eggs and adults.
Stage duration strongly dependent on temperature
Naupliar survival strongly dependent on food.
Reproduction & growth in upper layers (
Coupling Life-Cycle to Physical Oceanography
The modelling challengeThe Challenge Physiologically and spatially explicit demographic model Ocean-basin scale advection plus diffusion Hypothesis tests require wide parameter exploration Need exceptional computational efficiency
The Solution Focus on Calanus (physical and biotic environment as given) Separate computation of physical and biological components Discrete-time approach ( 104 speed-up relative to Lagrangian ensemble)
A Calanus-focussed model
Representing Physical TransportUpdate at regularly spaced times: TiClass abundance just before updateClass abundance just after updateTransfer matrix element from y to x for period to Ti. Determine by particle tracking in flow fields from GCM plus random (diffusive) component.
The Biological Model Uniform physiological age for each group of stages Development rate a function of temp. and food Diapause entry from start of C5 stage cued by low food
Updating the Biological ModelUpdate all classes in given group at given location at times {Ux,i} such thataccording towhereSurvival of individual in q at x over increment up to u
Updating the system stateCollect all un-processed updates from the adult, surface developer and diapauser groupsForm the union of the subsets of each sequence which fall before the next transport updateProcess the new sequence in time order, updating all classes in that group at that location at each operation. For each cell, in turn:Do next transport update, Output state variables.Produces model realisations in good agreement with PDE and Lagrangian ensemble solutions, but MUCH faster.
Prototype - EnvironmentFlow(HAMSOM)Temp.(HAMSOM)Food(SeaWiFS)Winter (day 42)Spring(day 133)Summer(day 217)Autumn(day 308)
Prototype diapause control hypotheses
Entry
Exit
H1
low food
development at depth
H2
photoperiod
development at depth
H3
low food
photoperiod
H4
photoperiod
photoperiod
N.E. Atlantic - test dataOverall plausibility testContinuous Plankton Recorder surveys (SAHFOS) Winter surveys of resting stages StonehavenFoinavenMurchisonOcean Weathership MFaroe shelfSaltenfjordenWestmann Islands
Hypothesis Testing - OWS MikeSurface CopepoditesDiapausersNewly surfaced overwinterersNo diapausers in springSharp drop at awakeningH1H1H3H3
Plausibility test DiapausersH1:H3:Winter (day 28)Spring (day 154)Summer (day 224)Autumn (day 336)
Plausibility test Surface CopepoditesH1:H3:Winter (day 28)Spring (day 154)Summer (day 224)Autumn (day 336)
Prototype - Conclusions Spatially and physiologically resolved model on an ocean basin scale can be made fast enough for wide-ranging parameter exploration
Current data on C. finmarchicus abundance in the N.E. Atlantic is best fitted by a model which assumes diapause is initiated by low food conditions.
Models which assume diapause duration is determined by development are invariably falsified
Awakening must be conditioned on a highly spatially correlated cue such as photoperiod.
Test Data Time Series & CPR
Prototype Model - Time Series Test Gulf of MaineOWS MikesurfaceC5-C6
diapauseC5
Prototype Model CPR TestobservedJan./Feb.May/Jun.Jul./Aug.observedpredicted
C5s & phytoplankton carbon at OWSM Diapause occurs at end of C5 stageFixed fraction of each generation
Annual Mean Temperature & FoodLabrador Sea is cold=> temperature-dependent background mortality
Revised Model - Time Series Test Gulf of MaineOWS MikesurfaceC5-C6
diapauseC5
Revised Model CPR TestJan./Feb.May/Jun.Jul./Aug.observedpredicted
Yearly Population Cycle
The Impact of Transport
Domain ConnectivityYear 1Year 3Year 6
ConclusionsFractional diapause entryDiapause entry late in C5Photoperiod-cued diapause exitTemperature-dependent mortality
Limited impact of transportHigh domain connectivityMatching Calanus demography =>Fitted model =>Ocean-scale population model feasibleNumerical efficiency is key
