Development of the Lipid Accumulation Window hypothesis to explain Calanus finmarchicus dormancy Jeffrey Runge School of Marine Sciences, University of Maine and Gulf of Maine Research Institute Andrew Leising NOAA, Southwest Fisheries Science Center Catherine Johnson University of British Columbia

Objectives: Identify environmental processes that control dormancy in Calanus finmarchicus Develop a mechanistic understanding of dormancy for inclusion in population dynamics modeling Approach: Compile Calanus and environmental data across regions in the NW Atlantic Look for common patterns and cues Using an individual-based model, develop quantitative hypotheses to explain patterns

Data Sources and Collaborators Data from: DFO – AZMP: 1999 – 2005 (E.Head, P.Pepin) DFO – IML:1990 – 1991 (S. Plourde, P. Joly) US-GLOBEC: 1995 – 1999 (E. DurbIn, M. Casas) PULSE – NEC: 2003 – 2005 (R. Jones)

Proxies for dormancy entry and exit Entry (Onset) Fifth copepodid (CV) half-max proxy Dormant when… CV proportion ≥  x / 2 where  x = average max. CV proportion over all years Exit (Emergence) Emergence when… 1. Adult (CVI) proportion ≥ Back-calculation from early copepodid appearance, using development time-temperature relationship Dormancy

AG: Anticosti Gyre, NW Gulf of St. Lawrence Stage Proportion Abundance (no. m -2 ) Onset Emergence

Possible dormancy cues Onset Photoperiod (Miller et al., 1991) Temperature (Niehoff & Hirche, 2005) Food availability (Hind et al., 2000) Lipid accumulation (hormonal link?) (Irigoien, 2004) Emergence Photoperiod (Miller et al., 1991; Speirs et al., 2004) Disturbance (Miller & Grigg, 1991) Development (Hind et al., 2000)

Climatological temperature at 5 m Onset Emergence Day of Year Temperature (°C) Rimouski Anticosti Gyre Newfoundland Scotian Shelf

Mean chlorophyll-a, 0 – 50 m Chl-a (mg m -3 ) Rimouski Anticosti Gyre Newfoundland Scotian Shelf Onset Emergence Day of Year --- half-saturation [Chl-a]

Analysis of variance Fp Multiple comparisons OnsetYear day22.32<0.001S27=AG; AG=RIM Day length18.38<0.001S27=AG; AG=RIM Temperature8.059<0.001S27=AG,H2; AG=H2 Chlorophyll

Conclusions No single observed environmental cue explains dormancy patterns Dormancy entry and emergence occur over a broad range of times, both among individuals and years The mechanistic understanding of dormancy transitions must involve interaction of multiple environmental factors. We develop a “lipid-accumulation window” hypothesis to explain observed life history patterns.

Miller et al Growth rules in the marine copepod genus Acartia. L&O. 22: Lipid accumulation window hypothesis: Development rate increases faster with temperature than growth rate Lipid production integrates temporally variable food and temperature history We hypothesize cue for entry occurs prior to stage CV. Mortality also influences probability of reaching CV dormant stage Individuals can only enter dormancy if their food and temperature history allows them to accumulate sufficient lipid

Lipid accumulation window hypothesis: Step 1:Decision to enter dormancy in stage CV is made in stage CIV. Criterion is attainment of 30% lipid content by wt. Food index

Durbin et al. 2003: Gulf of MaineRunge et al. (2006.): Georges Bank Calanus finmarchicus: Relationship of egg production to phytoplankton biomass

Lipid accumulation window hypothesis: Step 2 - Temporal Filter Time Favorable Env. Conditions Cumulative conditions that will allow dormancy in CIV and CV Lipid Threshold

Lipid accumulation window hypothesis: Step 2 - Temporal Filter Time Favorable Env. Conditions Cumulative conditions that will allow dormancy Resulting period when they go dormant

Lipid accumulation window hypothesis: Step 3 - Emergence Timing linked to Entry Emergence survival linked to entry and Env. Time Favorable Env. Conditions Jan Population entering dormancy Population exiting dormancy Successful females Dormancy Length, f(T during dormancy,% lipids at entry)

AG

Anticosti Gyre climatology

Anticosti Gyre Model simulation Observed climatology

Rimouski Observed climatology Model simulation

Next Steps Work on parameters for model for C. finmarchicus; development of general set for all of NW Atlantic Test LAW model against C. finmarchicus life cycle data sets in the NW Atlantic. Does the model reproduce variability in individual years? Test refined and alternative hypotheses- Additional conditions required? Examine mechanisms for emergence from dormancy: parameterization of Saumweber and Durbin functions for potential diapause duration Examine influence of climate change scenarios on Calanus life cycle and population dynamics Further testing with time series observations, include measures of lipid levels in CIV and CV