Transcript Belfast - Department of the Environment

Restoration of keystone species of benthic filter
feeders in temperate estuaries and embayments:
application of lessons from oyster restoration in the
Chesapeake Bay to mussel restoration in Strangford
Lough, Ireland.
Roger Mann
Professor and Director for Research and Advisory Services
Virginia Institute of Marine Science
Gloucester Point, VA 23062 USA
e-mail: [email protected]
phone 804/684-7108
Restoration:
1. you are not alone
2. It’s a whole watershed
problem.
map copyright to:
Chesapeake Bay Foundation,
Annapolis MD.
Do not use without permission.
Chesapeake Bay facts
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10,000 years old
298 km long
8484 sq km area
71.5 x 109 m3 volume
165,700 km2 watershed
15 million people, add 3 million more by 2025
90% forested watershed in colonial times,
60% now
The oyster harvest in 1885 would cover a
soccer pitch 600 ft deep.
The current Virginia annual dock side landings
of oysters from the wild fishery are worth less
than one exotic car.
map copyright to:
Chesapeake Bay Foundation, Annapolis MD
Do not use without permission.
If restoration is our goal we
need a benchmark to start.
(what is your benchmark?)
for oysters…..
Consider (1) the evolution of
the species, and (2) its recent
undisturbed habitat prior
period to European
colonization: what do we
want to restore it to?
Art copyright to:
Virginia Institute of Marine
Science. Do not use without
permission.
Start at the beginning - what is an oyster? A few
thoughts on the evolution of the Crassostrea form
(when I say oyster you think Modiolus)
• The genus Crassostrea is a primitive bivalve form with a complex life history
(benthic sessile adult, pelagic larva) and global distribution.
• The Crassostrea form can be traced to the Cretaceous – the time of the
Tyrannosaur. They have forsaken one adductor muscle and the foot to adopt a
sessile monomyarian form. Other than some of the scallops they are
effectively the only family within the 8,000 or so species of bivalves that
have done this. How have they overcome the apparent deficiencies
associated with these losses? They form reefs! Despite the primitive form
their longevity and abundance illustrate that fact that their life history
characteristics serve the “occupied”niche very well.
More thoughts on the oyster form and evolution
• Current life history theory argues there is a high level of independence
in the selection and adaptive response of the larval and adult forms BUT we must view these in appropriate time frames.
• Pelagic larval forms are considered primitive rather than derived there is remarkable conservatism among bivalve larval form.
• Members of the genus Crassostrea and their predecessors have
succeeded over geological time by opportunistically invading
ephemeral (in a geological time frame) coastal habitats.
And yet more evolution thoughts
• Ephemeral habitats are invaded by pelagic larval stages , and maintained by
long lived adults in aggregated, complex, geologically stable populations reefs. Without reefs fertilization efficiency at the population level would be
terminally low and the genus would have probably suffered extinction.
•
Reefs form critical protective habitat for early post settlement stages given
that these stages cannot move.
• With changes in climate, sea level and other environmental forces such
populations can expand, remain stable with limitations, or exhibit local
extinction.
• Despite local extinction there is little chance of species (within a genus) or
genus (as a whole) extinction given the demonstrated longevity in the
geological record, the latitudinal range of establishment (biogeography)
and the implied broad genetic diversity in either a genotypic or phenotypic
sense.
And final oyster evolution thoughts
• The underlying observation must be proffered that the genus (and
therefore included species) have inherent capability to occupy a broad
range of localized habitats.
• This capability probably DOES NOT have inherent capability to rapidly
evolve to include new genotypes (why should it given the demonstrated
capability to survive over evolutionary time?) in response to the
ephemeral habitat changes. This argument is then against a continued
rapid and “fluctuating” evolution in response to selective pressure from
ephemeral environments - they respond badly to rapid increases in stress.
• Finally (!), I extend the suggestion of conservatism to include larval
behavior. While are fascinated by 3D hydrodynamic models of larval
dispersal,but remember that pelagic larvae evolved primarily to allow
exploitation of feeding in the water column, and secondarily to effect
dispersal and genetic exchange between populations.
• Against this background we will track the decline and
attempts at restoration of the Virginia oyster.
Post colonial
exploitation was
uncontrolled
Art copyright to:
Virginia Institute of Marine Science.
Do not use without permission.
The Virginia tradition of hand tonging for oysters: fishing is not
the problem - fishing regulation and enforcement is the problem.
Art copyright to:
Virginia Institute of Marine Science. Do not use without permission.
Pursued with enthusiasm until the mid 1980’s, when diseases became
overwhelming and restoration needs were finally acknowledged.
Art copyright to: Virginia Institute of Marine Science. Do not use without permission.
The practical approach at landscape scale
Art copyright to:
J.M. Harding and Center for Coastal Resources Management respectively,
Virginia Institute of Marine Science. Do not use without citation.
We are here today to talk about restoration
strategies, what are they?
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Simple! A resource management equation
In decline R < M + F
In rebuilding R > M + F
How do we increase R, and decrease both M and F ?
What are the components of each and how do we
manipulate them?
• The important point is to think in common currency.
Target systems: Piankatank and Great Wicomico Rivers
(note the history and the basin morphology, circulation)
Art copyright to: Center for Coastal Resources Management,
Virginia Institute of Marine Science. Do not use without citation.
The simplest concept - just rebuild habitat
This appreciates but
minimizes issues of
long lived life history
strategy, multiple
year classes, periodic
recruit failure, and
non linearity of the
time course of
community response
to stress. But let’s try
it anyway!
Artwork by Kent Forrest with
copyright to Virginia Institute
of Marine Science. Do not
reproduce or use without
permission.
“If you build it they will come.” Kevin Costner, Field of Dreams..
and $100,000 later you get a reef.
Art copyright to:
J.M. Harding, Virginia Institute of Marine Science and J. A. Wesson, Virginia Marine
Resources Commission. Do not use without citation.
In some instances we do observe >1 year of oyster recruitment in
succession, but it is not consistent.
Consider the Piankatank River at Palaces Bar Point, before 1999 only reef
building, 1999 onwards included addition of brood stock oysters on
adjacent reefs.
Data courtesy of J. A. Wesson, Virginia Marine Resources Commission.
400
Mean Number Per Meter
350
300
250
Spat
Small
Market
200
150
100
50
0
1997
1998
1999
Years
2000
2001
Shell Bar in the Great Wicomico ($50,000 in shell) - the serendipitous brood
stock addition experiment ($50,000 of oysters) of 1996 resulted in egg
production of 4.5 billion m-2 and 37,000 larvae m-3 ! Aggregation works!
Art copyright to:
J.M. Harding, Virginia Institute of Marine Science. Do not use without citation.
Q: Can we manipulate recruitment?
A: Both Yes and No.
Consider the Great Wicomico at Shell Bar after 1996 brood stock oyster
additions.
Mean Number Per Meter
Data courtesy of J. A. Wesson, Virginia Marine Resources Commission.
900
800
700
600
500
400
300
200
100
0
Spat
Small
Market
1997
1998
1999
Ye ars
2000
2001
And the remainder of the
system is not simple
either!
Reefs really are the
structural and biological
cornerstones of the
estuarine ecosystem.
Figure from:
O’Beirn, F, Luckenbach, M, Mann, R,
Harding, J, and Nestlerode, J. 1999.
Ecological functions of constructed
oyster reefs along an environmental
gradient in Chesapeake Bay. Final
report submitted to Chesapeake Bay
Program, Annapolis, MD by the
Virginia Institute of Marine Science,
Gloucester Pt., VA.
Do not reproduce or use
without proper citation.
So what have we learned so far?
• We have increased recruitment immediately following sanctuary
construction, particularly when broodstock are added
• Natural mortality remains higher than stable reefs in the low salinity
sanctuary of “upriver” in the James, especially early post settlement
mortality.
• Recruitment is not maintained in subsequent years at initial levels in
higher salinity - is this a substrate issue, a disease issue, or a larval
supply issue?.
• Only limited populations of spawning oyster, both in terms of numbers
and year class representation, develop on the sanctuary reefs - this is
both a predation and a disease issue.
• We need lower natural M at all ages to increase the number and size of
the spawning stock and sustain recruitment to form stable populations
• Continued egg production from these reefs is modest, and even basic
simulations suggest this is inadequate to sustain a dense population.
Look again - Its all about metapopulation dynamics!
Art copyright to: Center for Coastal Resources Management,
Virginia Institute of Marine Science. Do not use without citation.
• Patchy environment within a semi closed circulation
• Consider Birth, Immigration, Emigration and Death models (BIDE)
stable population states in each patch, some sources and some sinks in
larval exchange.
• So we need to think at the holistic approach, but what is the scale and
can we model it?
I think we can model it in a design mode….
• We need an age structured
growth and mortality model.
• We need to divide M into
components of predation,
disease and anything else….
• We need better maps of
bottom habitat.
• THEN, we need to link R, M
and F in a rebuilding model.
Can we do this? I think yes,
we just have to use a
common currency.
Art copyright to:
J.M. Harding Virginia Institute of Marine
Science and Carl Cerco, US Army Coprs
of Engineers. Do not use without citation.
So, we model it - An example from Horsehead in the James River
(unpublished data, Roger Mann, Virginia Institute of Marine Science)
1995
1994
1993
70.0
50.0
45.0
45.0
40.0
60.0
40.0
35.0
50.0
35.0
30.0
30.0
40.0
25.0
25.0
30.0
20.0
20.0
15.0
15.0
10.0
10.0
5.0
5.0
20.0
10.0
3
3
12
11
3
10
93
83
73
63
1998
1997
60.0
53
43
33
23
3
3
3
3
12
11
10
93
83
73
63
53
43
33
23
3
13
3
3
3
12
11
93
10
83
73
63
53
43
33
23
13
3
1996
13
0.0
0.0
0.0
45.0
40.0
40.0
35.0
50.0
35.0
30.0
30.0
40.0
25.0
25.0
20.0
30.0
20.0
15.0
15.0
20.0
10.0
10.0
5.0
5.0
3
12
3
11
3
10
93
83
73
63
53
43
33
3
3
3
3
12
11
93
10
83
73
63
53
43
33
23
13
3
3
3
3
12
11
93
10
83
73
63
53
43
33
23
13
3
23
0.0
0.0
0.0
13
10.0
Est im at ed oyster growth in t he James River
using field observat ions and an oscillat ing
Von Bert alanffy growt h descript or
100.00
60.00
L(t)
40.00
20.00
-20.00
YEAR
6.67
6.25
5.84
5.42
5.00
4.58
4.16
3.75
3.33
2.92
2.50
2.09
1.67
1.25
0.84
0.00
0.42
data in press: Roger Mann and
David A. Evans. J. Shellfish
Research, Sheridan Press
80.00
Shell height (mm)
Then start with a
growth curve and
re-cast size
demography as age
demography
data in press: Roger Mann and David A. Evans. J. Shellfish Research, Sheridan Press
Horsehead year class structure: 1993-1998
160.0
140.0
oysters/sq.m
120.0
0
1
100.0
2
80.0
3
4
60.0
5+
40.0
20.0
0.0
1993
1994
1995
1996
year
1997
1998
To summarize and simplify Mann and Evans (1998, 2004, Journal of Shellfish
Res.), recruitment to the 25mm size class is estimated from larval supply thus:
(Ftot x Fq x Fs x Fd x Ff ) x (1- exch)2d x (1-Lmort)d x Psub x Pfoul x Pmet x (1Jmort)dp
then we need to expand this to age specific mortality
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Ftot I total egg production
Fq is sex ratio
Fs modifies for salinity
Fd modifies for disease
Ff fertilization efficiency
(1- exch)2d accounts for
loss by dispersal
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(1-Lmort)d is larval mortality
Psub is substrate availability
Pfoul is fouling
Pmet is % metamorphosis
(1- Jmort)dp is juvenile mortality
Start with population demographics and abundance,
vary age specific M, then estimate R…..
data in press: Roger Mann and David A. Evans. J. Shellfish Research, Sheridan Press
Year class structure
Cum ulative m or tality
1.20
100
1.00
% cumulative mortality
120
#/sq.m
80
60
40
20
0.80
0.60
A
0.40
B
C
D
0.20
E
0.00
0
1
2
3
4
Disease chal lenge wi th successi ve year s
5
0
1
2
3
4
5
Ye ar clas s
6
7
8
Example #1 of estimated recruitment at 25mm
data in press: Roger Mann and David A. Evans. J. Shellfish Research, Sheridan Press
10% loss per tidal exchange, 21 day l ar val per iod
9000
60
8000-9000
7000-8000
6000-7000
8000
7000
5000
4000
2000-3000
1000-2000
0-1000
3000
2000
0.05
1000
larv al
mortalit y
rate
0.07
0
A
B
C
D
recruitment : #/sq.m
5000-6000
4000-5000
3000-4000
6000
0.25
E
50
50-60
40
40-50
30-40
30
20-30
10-20
0-10
20
10
0.05
0.07
0
A
B
C
populat ion st ruct ure
populat ion st ruct ure
10% loss per tidal exchange, 25 day larv al period
2500
2000-2500
recruitment : #/sq.m
recruitment : #/sq.m
20% loss per tidal exchange, 21 day lar val per iod
2000
1500-2000
1000-1500
1500
500-1000
0-500
1000
500
0.05
0.07
0
A
B
C
populat ion st ruct ure
D
0.25
E
larv al
mortalit y
rate
D
0.25
E
larv al
mortalit y
rate
Example #2: where stress causes 25% reduction in fecundity
data in press: Roger Mann and David A. Evans. J. Shellfish Research, Sheridan Press
15% loss per tidal exchange, 21 day larv al per iod
10% loss per tidal exchange, 21 day larv al period
600
7000
5000-6000
5000
4000-5000
recr uitment: #/sq.m
6000
3000-4000
4000
2000-3000
3000
1000-2000
0-1000
2000
0.05
1000
larv al
mor tality
rate
0.07
0
A
B
C
0.25
D
500
500-600
400-500
400
300-400
200-300
300
100-200
0-100
200
100
0.05
0.07
0
A
B
E
population structure
population structure
10% loss per tidal exchange, 25 daylarval period
1800-2000
2000
recr uitment: #/sq.m
recr uitment: #/sq.m
6000-7000
1800
1600-1800
1400-1600
1600
1400
1200-1400
1000-1200
1200
1000
800
600
800-1000
600-800
400-600
200-400
0-200
400
200
0
0.05
0.07
A
B
population structure
C
D
0.25
E
larv al
mor tality rate
C
D
0.25
E
larv al
mor tality
rate
The lesson for Chesapeake Bay and Strangford Lough
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Restoration is a whole watershed issue
Whole ecosystem processes over extended periods can be causative
Long term responses of keystone organisms to cumulative stress can be very non linear
Immediate signals of ecosystem failure are difficult to see with long lived species
where individual year class signatures are subsumed in population demogaphics.
Failure of keystone species has cascading impacts on the remainder of the system
Restoration cannot be achieved on a piece by piece basis
Metapopulation processes and local circulation patterns can make or break your project
Watershed activities must be commensurate with in water activity
This is large scale ecological engineering, and biologists have only modest experience
in this field
The regulatory environment must support efforts. Public education is vital to make the
public stakeholders in the process.
Don’t assign blame, look forwards not backwards.
It is going to be very expensive.
Thank you
Come and visit our web site:
www.vims.edu/mollusc
Art copyright to:
J.M. Harding, Virginia Institute of Marine
Science. Do not use without permission.