Obey the LAW: Calanus finmarchicus dormancy explained

Jeffrey RungeSchool of Marine Sciences, University of Maine and

Gulf of Maine Research Institute

Andrew LeisingNOAA, Southwest Fisheries Science Center

Catherine JohnsonUniversity 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 individual-based models, develop quantitative hypotheses to explain patterns

Proxies for dormancy entry and exit

Entry: Fifth copepodid (CV) half-max proxy

Dormant when… CV proportion >= x-bar /2 where x-bar = average max. CV

proportion over all years

1. Exit:Emergence when…

1. Adult (CVI) proportion >= 0.1

2. Back-calculation from early

copepodid appearance, using

development time-temperature

relationship

Copepodids Nauplii

AdultsDormancyat CV stage

Data sources

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)

AG: Anticosti Gyre, NW Gulf of St. LawrenceS

tage

Pro

port

ion

Abu

ndan

ce (

no.

m-2)

Photoperiod at emergence and onset

Rimouski

Anticosti Gyre

Newfoundland

Scotian Shelf

Day

leng

th (

h)

Day of Year

Emergencedate

Previousand nextdate

Temperature at 5 m

Tem

pera

ture

(°C

)

Rimouski

Anticosti Gyre

Newfoundland

Scotian ShelfOnsetEmergence

Climatological temperature at

5 m

OnsetEmergence

Rimouski

Anticosti Gyre

Newfoundland

Scotian Shelf

Tem

pera

ture

(°C

)

Mean chlorophyll-a, 0 – 50 m

Chl

-a (

mg

m-3)

Rimouski

Anticosti Gyre

Newfoundland

Scotian Shelf

Chl-a values truncated at 1.6 mg m-3

(threshold forgrowth)

Onset

Emergence

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 propose a “Lipid-Accumulation Window” hypothesis to explain observed life history patterns.

Growth of Neocalanus plumchrus copepodids in the southeastern Bering Sea

Development time is a function of temperature and food concentration in Calanus finmarchicus

Campbell, R. M. Wagner, G. Teegarden, C. Boudreau and E. Durbin. 2001. Growth and development rates of the copepod Calanus finmarchicus reared in the laboratory. Mar. Ecol. Prog. Ser. 221: 161-183

Miller et al. 1977.Growth rules in the marine copepod genus Acartia. L&O. 22: 326-335.

Lipid Accumulation Window hypothesis:Step 1 - Conditions allowing dormancy: suppose only copepods with > 50% lipid content can enter

Integrated Temperature

Integrated

Food

Fraction lipid content at end of CV stage

0.0

0.5

0.1

0.2

0.3

0.4

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 - Predation Filter

Time

Favorable Env. Conditions

Predation Removal here

Resulting population entering dormancy

Missing cohort here

Lipid accumulation window hypothesis: Step 4 - Emergence Timing linked to Entry

Emergence survival linked to entry and Env.

Time

Favorable Env. Conditions

JanJan

Population entering dormancy

Population exiting dormancy

Successful females

Dormancy Length, f(T during dormancy,% lipids at entry)

Testing the hypothesis1. Identify lipid accumulation windows by starting individual-based

model runs, driven by temperature and chlorophyll, at each date

Time

Chl

orop

hyll

(mg

m-3)

Tem

pera

ture

(°C

)

…

Pot

entia

l lip

id

accu

mul

atio

n

Time

Threshold for onset of dormancy

2. CVs produced during the lipid accumulation window can enter dormancy

Utility of the model for this calculation• Growth and development are decoupled• Ability to include temporally variable forcing data (food

and temperature)• Can include or ignore predation filter• Mechanistic and physiological basis for growth and

developmentExample for Calanus pacificus

0

20

40

60

80

100

120

140

0 10 20 30 40 50

Time (days)

Weig

ht

(µg

C)

Model 8 DegreesModel 12Model 16Observed Data 8Observed Data 12Observed Data 15.5

Example Results for C. pacificus

•Top figure is based on climatology from NH20, Newport Line, OR; Bottom figure based on SCB climatology

•In the south, copepods spawned as early as day 50 can enter dormancy, whereas in the north, it’s 40 days later.

•Peak dormancy entrance date is between days 125-175 in the S, and between days 175-225 in N.

•Predation during the “Green” period would remove potentially successful copepods

•Suboptimal cold temperatures(and low food) in the N during the early part of the year limit success then, whereas overly warm temperatures later in the year limit success in S during that time (recall the optimal window)

Final Conclusions• Our findings for C. finmarchicus, C. pacificus and C.

marshallae strongly suggest that multiple environmental factors are the likely cues for dormancy, as these copepods enter and exit dormancy over a wide range of times and conditions.

• Our modeling results (for C. pacificus so far) suggest that lipid accumulation (or some equivalent storage compound) is a likely player in how dormancy is triggered.

• OBEY THE LAW!!!!

Implications

• Previous coupled 3-d physical-biological models of Calanus have forced dormancy transitions empirically using an advective-diffusive approach

• While these models provide diagnostic insight, they cannot be used for prediction

• A mechanistic, coupled IBM-physical model that tracks lipid accumulation is needed to understand and predict Calanus population responses to climate changes