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: rmann@vims.edu

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• 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 MDDo 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?

• 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.

0

50

100

150

200

250

300

350

400

Mea

n N

umbe

r P

er M

eter

1997 1998 1999 2000 2001Years

SpatSmallMarket

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.

Data courtesy of J. A. Wesson, Virginia Marine Resources Commission.

0

100

200

300

400

500

600

700

800

900

Mea

n N

um

ber

Per

Met

er

1997 1998 1999 2000 2001Years

SpatSmallMarket

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)

1993

0.0

5.0

10.0

15.0

20.0

25.0

30.0

35.0

40.0

45.0

3 13 23 33 43 53 63 73 83 93 103

113

123

1994

0.0

5.0

10.0

15.0

20.0

25.0

30.0

35.0

40.0

45.0

50.0

3 13 23 33 43 53 63 73 83 93 103

113

123

1995

0.0

10.0

20.0

30.0

40.0

50.0

60.0

70.0

3 13 23 33 43 53 63 73 83 93 103

113

123

1996

0.0

10.0

20.0

30.0

40.0

50.0

60.0

3 13 23 33 43 53 63 73 83 93 103

113

123

1997

0.0

5.0

10.0

15.0

20.0

25.0

30.0

35.0

40.0

45.0

3 13 23 33 43 53 63 73 83 93 103

113

123

1998

0.0

5.0

10.0

15.0

20.0

25.0

30.0

35.0

40.0

3 13 23 33 43 53 63 73 83 93 103

113

123

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

Estimated oyster growth in the James Riverusing field observations and an oscillating

Von Bertalanffy growth descriptor

-20.00

0.00

20.00

40.00

60.00

80.00

100.00

0.42

0.84

1.25

1.67

2.09

2.50

2.92

3.33

3.75

4.16

4.58

5.00

5.42

5.84

6.25

6.67

YEAR

She

ll he

ight

(m

m)

L(t)

Horsehead year class structure: 1993-1998

0.0

20.0

40.0

60.0

80.0

100.0

120.0

140.0

160.0

1993 1994 1995 1996 1997 1998

year

oyste

rs/s

q.m 0

1

2

3

4

5+

data in press: Roger Mann and David A. Evans. J. Shellfish Research, Sheridan Press

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 (1- Jmort)dp

then we need to expand this to age specific mortality

• 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

• (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

0

20

40

60

80

100

120

1 2 3 4 5

Disease challenge with successive years

#/s

q.m

Cumulative mortality

0.00

0.20

0.40

0.60

0.80

1.00

1.20

0 1 2 3 4 5 6 7 8

Year class%

cu

mu

lati

ve m

ort

ality

A

B

C

D

E

Example #1 of estimated recruitment at 25mm data in press: Roger Mann and David A. Evans. J. Shellfish Research, Sheridan Press

A B C D E0.25

0.07

0.05

0

1000

2000

3000

4000

5000

6000

7000

8000

9000

recr

uit

ment:

#/s

q.m

population structure

larval mortality

rate

10% loss per tidal exchange, 21 day larval period

8000-9000

7000-8000

6000-7000

5000-6000

4000-5000

3000-4000

2000-3000

1000-2000

0-1000

A B C D E0.25

0.07

0.05

0

10

20

30

40

50

60

recr

uit

ment:

#/s

q.m

population structure

larval mortality

rate

20% loss per tidal exchange, 21 day larval period

50-60

40-50

30-40

20-30

10-20

0-10

A B C D E0.25

0.07

0.05

0

500

1000

1500

2000

2500

recr

uit

ment:

#/s

q.m

population structure

larval mortality

rate

10% loss per tidal exchange, 25 day larval period

2000-2500

1500-2000

1000-1500

500-1000

0-500

Example #2: where stress causes 25% reduction in fecundity data in press: Roger Mann and David A. Evans. J. Shellfish Research, Sheridan Press

A B C D E0.25

0.07

0.05

0

1000

2000

3000

4000

5000

6000

7000

recru

itm

en

t: #

/sq

.m

population structure

larval mortality

rate

10% loss per tidal exchange, 21 day larval period

6000-7000

5000-6000

4000-5000

3000-4000

2000-3000

1000-2000

0-1000

A B C D E0.25

0.07

0.05

0

100

200

300

400

500

600

recru

itm

en

t: #

/sq

.m

population structure

larval mortality

rate

15% loss per tidal exchange, 21 day larval period

500-600

400-500

300-400

200-300

100-200

0-100

A B C D E0.25

0.07

0.05

0200400

600

8001000

1200

1400

1600

1800

2000

recru

itm

en

t: #

/sq

.m

population structure

larval mortality rate

10% loss per tidal exchange, 25 day larval period

1800-2000

1600-1800

1400-1600

1200-1400

1000-1200

800-1000

600-800

400-600

200-400

0-200

The lesson for Chesapeake Bay and Strangford Lough

• 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 youCome 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.