Blue crab: ecology and exploitation in a changing

climate.

Thomas Miller and Hillary Glandon Chesapeake Biological Laboratory

University of Maryland Center for Environmental Science Solomons, MD

miller@umces.edu @tomatcbl

Sustainable Fisheries GIT

Najjar et al. 2010

Chesapeake Bay Climate

Boesch et al. 2008

Climate Change in Estuaries

Kelly et al. 2011

pH variability (1985-2012)

Estuarine environments naturally variable Gradients within

estuaries spatially, seasonally and inter-annually

O.A. v3.0

Blue crab are complex calcifiers Mobilize Ca++ and HCO3-

on every molt Energetically costly

http://mddnr.chesapeakebay.net/eyesonthebay/index.cfm

7.8

7.4

8.1

Ocean Acidification

Growth Growth by molting May molt up to 20

times to reach adult size

Characterized by periods of stasis and rapid increases in size, during which the shell is soft

0

2

4

6

8

10

12

14

5/30/1997 7/19/1997 9/7/1997 10/27/1997

Inter-molt period

Growth per molt

Growth per molt

y = 1.2678x - 4.4108R² = 0.9257

y = 1.286x - 3.9252R² = 0.9568

y = 1.2237x - 2.8213R² = 0.9609

0

20

40

60

80

100

0 20 40 60 80

16 C

20 C

24 C

Brylawski et al. 2006 Initial Size (mm)

Fina

l Siz

e (m

m)

Bilen et al. 2014

Y=1.16x + 1.08 R2=0.993

Intermolt period Intermolt period

decreases significantly with temperature

Development rate increases with temperature and predicts overwintering at ~10-11oC

IMP increases slightly with size

0

0.01

0.02

0.03

0.04

0.05

0.06

8 13 18 23 28 33Temperature (oc)

Deve

lopm

ent r

ate

(/day

)

0

20

40

60

80

100

120

140

160

180

IMP

(Day

s)

Temperature (oC)

Methods: Acidification Growth Experiment

Results: Growth Experiment

05

1015202530

Ambient High

Gro

wth

per

Mol

t (%

)

Temperature

Molt 1 AmbpCO2Molt 2 AmbpCO2Molt 1 HighpCO2Molt 2 HighpCO2

0

2

4

6

8

10

12

14

16

Ambient High

Inte

r-m

olt P

erio

d (D

ays)

Temperature

Ambient pCO2High pCO2

0

5

10

15

20

25

30

Ambient High

Food

Con

sum

ptio

n (%

of C

rab

Mas

s)

Temperature

P>0.05

Temp: P=0.002 pCO2: P>0.05

Temp: P=0.007 pCO2: P>0.05

Conclusions: Temperature Effects Response Temperature

Growth per Molt No effect Growth Rate Increase Consumption Increase

Gut Energy Content No effect Muscle Energy Content No effect Carapace Thickness Decrease*

Carapace [Ca] Decrease Carapace % CaCO3 Decrease

Carapace [Mg]# Increase

In warmer water, crabs grew faster and ate more food but did not change their energy storage patterns These crabs had thinner shells with less [Ca], lower %CaCO3, and more [Mg].

Bigger in less time Increased food consumption Molting more frequently Less protective shell

= Faster Growth

Conclusions: pCO2 Effects

Crab growth was not impacted in more acidic water, but energy storage was decreased. These crabs also had thinner shells but with more [Ca], higher %CaCO3, and more [Mg].

Less stored energy Less protective shell (?) = Maintenance of

Growth

Response pCO2 Growth per Molt No effect

Growth Rate No effect Consumption No effect

Gut Energy Content Decrease Muscle Energy Content Decrease Carapace Thickness Decrease*

Carapace [Ca] Increase* Carapace % CaCO3 Increase*

Carapace [Mg]# Increase

So what is the impact on the population

Seasonal model Stage based

probabilities are functions of M, F, and f, the “growth” rate

Projection matrix A=Aw*As

Eigen analysis of A provides r=0, an index of Fmsy

Megalopae

Small Age 1

Large Age 1

Adult

O/WJuvenile

O/W SmallAge1

O/W LargeAge 1

O/W Adult

Summer Winter

Current conditions r=0 occurs at F=0.55

0 0.5 1 1.5 2-0.6

-0.5

-0.4

-0.3

-0.2

-0.1

0

0.1

0.2

0.3

F

r

Miller 2001

Changing conditions r=0 occurs at Fcrit=0.55 If increasing “growth”

rate doesn’t affect time to maturity then increasing

growth rotates the iscolines, leaving Fcrit relatively unaffected

0 0.5 1 1.5 2-0.7

-0.6

-0.5

-0.4

-0.3

-0.2

-0.1

0

0.1

0.2

0.3

F

r

Changing conditions r=0 occurs at Fcrit=0.55 If increasing “growth”

rate decreases time to maturity then increasing

growth shifts the isoclines, more than doubling Fcrit

0 0.5 1 1.5 2-0.6

-0.5

-0.4

-0.3

-0.2

-0.1

0

0.1

0.2

0.3

0.4

F

r

Changing conditions r=0 occurs at Fcrit=0.55 Decreasing winter

mortality increasing productivity of the stock, almost doubling the Fcrit value.

But this “benefit” only accrues provided the winter remains a “closed” period

0 0.5 1 1.5 2-0.6

-0.5

-0.4

-0.3

-0.2

-0.1

0

0.1

0.2

0.3

0.4

F

r

Stochasticity

Detection of patterns revealed in deterministic projections may be masked by stochasticity.

0 0.5 1 1.5 2-0.8

-0.6

-0.4

-0.2

0

0.2

0.4

0.6

F

r

Conclusions Growth and mortality are strongly temperature

dependent Population dynamics are highly variable, and

show latitundinal patterns Climate change has potential to dramatically

change timing of key life history transitions Ocean acidification imposes energetic costs on

blue crab – consequences remain to be quantified

Population dynamics of blue crab will change dramatically in next 30-50 yrs, presenting opportunities and challenges

http://hjort.cbl.umces.edu