Jo King: Mechanisms relating the ocean-scale distribution of Calanus finmarchicus to environmental heterogeneity Douglas Speirs 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 finmarchicus Omnivorous, 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 (<200m). Overwinters in a resting state at depths of m.

Coupling Life-Cycle to Physical Oceanography

The modelling challenge The 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 (  10 4 speed-up relative to Lagrangian ensemble)

A Calanus-focussed model

Representing Physical Transport Update at regularly spaced times: T i Class abundance just before update Class abundance just after update Transfer matrix element from y to x for period to T i. 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 Model Update all classes in given group at given location at times {U x,i } such that according to where Survival of individual in q at x over increment up to u

Updating the system state Collect all un-processed updates from the adult, surface developer and diapauser groups Form the union of the subsets of each sequence which fall before the next transport update Process 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 - Environment Flow (HAMSOM) Temp. (HAMSOM) Food (SeaWiFS) Winter (day 42) Spring (day 133) Summer (day 217) Autumn (day 308)

Prototype – diapause control hypotheses

Stonehaven Foinaven Murchison Ocean Weathership M Faroe shelf Saltenfjorden Westmann Islands N.E. Atlantic - test data Overall plausibility test Continuous Plankton Recorder surveys (SAHFOS) Winter surveys of resting stages

Hypothesis Testing - OWS Mike Surface Copepodites Diapausers Newly surfaced overwinterers No diapausers in spring Sharp drop at awakening H1 H3

Plausibility test – Diapausers H1: H3: Winter (day 28) Spring (day 154) Summer (day 224) Autumn (day 336)

Plausibility test – Surface Copepodites H1: 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 Mike surface C5-C6 diapause C5

Prototype Model – CPR Test observed Jan./Feb. May/Jun. Jul./Aug. observedpredicted

C5’s & phytoplankton carbon at OWSM Diapause occurs at end of C5 stage Fixed fraction of each generation

Annual Mean Temperature & Food Labrador Sea is cold => temperature-dependent background mortality

Revised Model - Time Series Test Gulf of MaineOWS Mike surface C5-C6 diapause C5

Revised Model – CPR Test Jan./Feb. May/Jun. Jul./Aug. observedpredicted

Yearly Population Cycle

The Impact of Transport

Domain Connectivity Year 1 Year 3 Year 6

Conclusions Fractional diapause entry Diapause entry late in C5 Photoperiod-cued diapause exit Temperature-dependent mortality Limited impact of transport High domain connectivity Matching Calanus demography => Fitted model => Ocean-scale population model feasible Numerical efficiency is key