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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
[email protected] @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