STAC Workshop 28 March 2017 Blue crab ecology and exploitation in a changing climate. Thomas Miller Chesapeake Biological Laboratory University of Maryland Center for Environmental Science Solomons, MD miller@umces.edu @tomatcbl
Global Warming
Variability in the Chesapeake Bay Mean ph 1985-2012 7.8 7.4 8.1 http://mddnr.chesapeakebay.net/eyesonthebay/index.cfm
Blue crab life history
Climate and recruitment Recruitment mechanisms poorly understood Recruitment strongly influenced by stock size Role of coastal currents Active behavior Stock recruit modeling suggests roles for June Sept wind stress in lower Bay River discharge (other systems)
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 14 12 10 8 6 4 Growth per molt Inter-molt period 2 0 5/30/1997 7/19/1997 9/7/1997 10/27/1997
100 80 16 C 20 C 24 C Growth per molt Final Size (mm) 60 40 20 y = 1.2678x - 4.4108 R² = 0.9257 y = 1.286x - 3.9252 R² = 0.9568 y = 1.2237x - 2.8213 R² = 0.9609 Y=1.16x + 1.08 R 2 =0.993 0 0 20 40 60 80 Brylawski et al. 2006 Initial Size (mm) Bilen et al. 2014
Intermolt period Intermolt period decreases significantly with temperature Development rate increases with temperature and predicts overwintering at ~10-11 o C IMP increases slightly with size Development rate (/day) IMP (Days) 180 160 140 120 100 80 60 40 20 0 0.06 0.05 0.04 0.03 0.02 0.01 0 8 13 18 23 28 33 Temperature (oc)( o C)
Overall growth Hines et al. 2010 Temperaturedependent increases in growth decrease time to specific life history events Increases in population productivity expected.
Reproduction From Hines et al. 2010 Period suitable for principal reproductive events increases with temperature Size at maturity tends to decrease with temperature Impacts on fecundity less clear
Climate and growth Limiting temperature (~9-11 o C) for growth induces overwinter dormancy. Above limiting temperature, growth well described by stochastic degree-day model Faster growth reduces time to key life history events Data needs: high spatial (<1 km) and temporal (daily) resolution bottom water temperature
So what in an acidified estuary?
Ocean Acidification CO 2(aq) + H 2 O (l) 11 H 2 CO 3(aq) 22 + H (aq) + HCO 3(aq) 33 + H (aq) 2 + CO 3(aq)
Methods: Acidification Growth Experiment
No effect of ph on growth
Conclusions: pco2 Effects Response Growth per Molt Growth Rate Consumption Gut Energy Content Muscle Energy Content Carapace Thickness Carapace [Ca] Carapace % CaCO3 Carapace [Mg] # pco2 No effect No effect No effect Decrease Decrease Decrease* Increase* Increase* Increase 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]. Maintenance of Growth = Less stored energy Less protective shell (?)
Climate and acidification For juvenile and adult crabs, acidification likely has little effect on growth Effects of larval stages unknown Potential energetic effect of acidification on ration and on carapace structure, suggesting impacts of acidification on predator-prey interactions. Data needs: Uncertain
But what about winter mortality?
1 0.8 Females % Survival 0.6 0.4 0.2 0 3C, 10ppt 3C, 25ppt 5C, 10ppt 5C, 25ppt 0 20 40 60 80 100 120 Time (days) 1 0.8 Males % Survival 0.6 0.4 0.2 0 3C, 10ppt 3C, 25ppt 5C, 10ppt 5C, 25ppt 0 20 40 60 80 100 120 Bauer and Miller 2010 Time (days)
Survival prediction Survival probability in each cell calculated by inputting the parameter estimates into the survival equation S(t) [ ] λ(β + β Temp+ β Sal β - t λ exp 0 1 2 + = exp Size) 3 Winter duration Average Temperature Average Salinity
Adjusted abundance Baywide Abundance (10 6 ) 1600 1400 Original 1200 Adjusted 1000 800 600 400 200 0 1990 1993 1996 1999 2002
Climate and mortality Strong temperature dependency on mortality Decrease in overwinter mortality with increasing winter temperature Assumed increase in mortality during growing season with temperature Data needs: (i) high resolution winter temperature maps, (ii) prediction of when overwintering will cease (underway), (iii) high resolution temperature fields during growing season
Life history patterns Growth seasonal Maturation within 24 months Prolonged exposure to sizedependent cannibalism Temperature-induced winter mortality limitation Growth continuous Maturation within 10-12 months Size-dependent cannibalism No temperature-induced winter mortality Growth seasonal Maturation within 18-24 months Moderate exposure to sizedependent cannibalism Temperature-induced winter mortality regulation in cold years Brylawski and Miller 2006 Bauer and Miller 2010 Hines et al. 2010
So what are the unknown questions Impacts of climate change on offshore portion of life-cycle largely unknown Impact of climate change on ecosystem components unclear Habitat Predators Is the space for time substitution valid for projections
Environmental gradients Average monthly temperature varies considerably over species range What is the consequence on growth and survival? Average temperature (oc) 25 20 15 10 5 Savannah, GA Chesapeake Bay Long Island Sound 0 Dec Feb Jan Mar Month
Quantifying spatial pattern
The Winter Dredge Survey (WDS) Conducted yearly since 1990 Winter crabs are dormant, no movement 1 minute tow of a crab dredge ~1,500 stations per year
1990-1991
2000-2001
Crab distribution maps 1990-91 2000-01 2008-09
300 Control rule - adult female abundance 250 Number of crabs (x 10 6 ) 200 150 100 50 0 1990 1995 2000 2005 2010 2015 Age 1+ females Threshold Target Year
Exploitation fractions (age-0+ females) 0.6 0.5 0.4 0.3 0.2 0.1 0.0 2016 Stock status N=70M 2016 0 50 100 150 200 250 300 Abundance of female age-1+ crabs (millions) U=0.34 U=0.25 N=215 M
http://hjort.cbl.umces.edu
Distribution Callinectes is a tropical genera that is widely distributed worldwide. Callinectes sapidus, the blue crab, is distributed from Venezuela, throughout the Caribbean, and up the eastern seaboard to New England.
Stochasticity 0.6 Detection of patterns revealed in deterministic projections may be masked by stochasticity. r 0.4 0.2 0-0.2-0.4-0.6-0.8 0 0.5 1 1.5 2 F
Number of crabs (x 10 6 ) 700 600 500 400 300 200 100 0 1990 1992 1994 1996 1998 2000 2002 2004 2006 2008 2010 2012 2014 2016 Year Age 0 abundance
Number of crabs (x 10 6 ) 600 500 400 300 200 100 Age 1+ abundance 0 1990 1992 1994 1996 1998 2000 2002 2004 2006 2008 2010 2012 2014 2016 Year
350 300 Age 1+ female abundance Number of crabs (x 10 6 ) 250 200 150 100 50 0 1990 1992 1994 1996 1998 2000 2002 2004 2006 2008 2010 2012 2014 2016 Year
Number of crabs (x 10 6 ) 300 250 200 150 100 50 Control rule - adult female abundance Age 1+ females Threshold Target 0 1990 1992 1994 1996 1998 2000 2002 2004 2006 2008 2010 2012 2014 2016 Year
Female blue crab harvest (x 10 6 ) 45 40 35 30 25 20 15 10 5 Maryland Virginia Potomac R MD average VA average PR average 0 1990 1992 1994 1996 1998 2000 2002 2004 2006 2008 2010 2012 2014 Year
Fraction females removed 80 70 60 50 40 30 20 10 0 Percent of females removed Female-specific target (25.5%) Female-specific threshold (34%) 1996 1998 2000 2002 2004 2006 2008 2010 2012 2014 Year
2016 Stock status 0.6 N=70M 0.5 2000 Exploitation fractions (age-0+ females) 0.4 0.3 0.2 0.1 2004 1999 2001 1998 2002 2007 1995 2003 1994 2006 1990 2005 1997 1996 2008 2014 2015 2012 2013 1992 1993 2009 2011 2016 1991 2010 U=0.34 U=0.25 0.0 0 50 100 150 200 250 300 Abundance of female age-1+ crabs (millions) N=215 M