Native Oyster Restoration in the Chesapeake Bay: Lessons for the

Delaware Estuary

Roger MannVirginia Institute of Marine Science

Gloucester Point, VA 23062

Generic lessons on oysters to be considered in

designing restoration protocols.

• 100,000 mollusc species, 8,000 bivalves.• Primitive form with a complex life

history [benthic sessile adult, pelagic larva (primitive, not derived form) and global distribution.]

• The form can be traced to the Cretaceous – the time of the Tyrannosaur.

• Most bivalves have adductor muscles and a foot - only the oysters and scallops have lost both the foot and one muscle, and at least the scallops generally learned how to swim.

• Oyster survival is all about occupation of space, aggregation, building of habitat, plastic form, predator protection for the juveniles, longevity, and arguably protandric hermaphroditism.

Specific lessons on the genus Crassostrea: part 1

• The genus succeeded over geological time by opportunistic invasion of ephemeral (geological time frame) coastal habitats.

• Invasion is by pelagic larvae and maintained by long lived adults in aggregated, complex, geologically stable populations -Reefs. Oyster create and maintain their own habitat (so much for essential fish habitat analogs).

• Reef aggregations increase fertilization efficiency at the population level. There are arguable advantages for protandry in combination with reefs (= parasitic or precocious males).

• Reefs form critical protective habitat for early post settlement stages given that these stages cannot move. This is facilitated by the plastic form of the adult.

Specific lessons on the genus Crassostrea: part 2

• Over time populations can expand, remain stable, or exhibit local extinction.

• Success is demonstrated by longevity in the geological record, latitudinal range, occupancy of a broad range of localized habitats (implies broad genotypic diversity and/or phenotypic plasticity.

• Probably DOES NOT include capability to rapidly evolve new genotypes in response to the ephemeral habitat changes -instead they go locally extinct.

• I suggest conservatism to include larval behavior. Pelagic larvae evolved primarily to allow exploitation of feeding in the water column, and secondarily to effect dispersal and genetic exchange between populations.

Chesapeake Bay facts • 10,000 years old• 298 km long• 8484 sq km area• 71.5 x 109 m3 volume• 165,700 km2 watershed

The current upstream problem• 15 million people, add 3 million more

by 2025.• 90% forested watershed in colonial

times, 60% now The current downstream status

• The oyster harvest in 1885 would cover a soccer pitch 600 ft deep.

• The current Virginia annual dock side landings of oysters vary in the 25-100,000 bushel range.

Lesson #1: Do the math before making public statements on expected end products.

Question #1: Restoration for water quality oyster is proffered to “clean up” the Bay - is this the case?

Examine question #1: Restoration water quality.

• The “Newell” number - the bay was filtered in 3 days.• Bay volume 71.5x 109 m3. Assume 75% is in the main stem and

unavailable for oyster filtration, and the impacts of any restoration will be in the remaining 25% of the volume in the sub estuaries and the shallow regions (where turbidity is higher challenging filtration, exacerbated by focus on nutrient rather than turbidity reduction).

• Consider 45, 000 acres of oyster habitat (restorable total in VA and MD combined) stocked with 100 adult oyster/square meter (higher than the most productive reefs in the James River) filtering at summer rates (1-2 L/hr based on Powell et al 1992, Figure 1, low rate) produces an estimated ability to filter all the water in that 25% in approximately 14 –28 days.

• Impacts on water quality will at best be modest and local.

Lesson #2: Do not underestimate cost.Question #2: How much will it costs to restore habitat to provide ecological services andhabitat complexity?

Examine question #2: Habitat restoration costs

• 45, 000 acres of restorable oyster habitat for VA and MD. • De novo shell planting to a basal 2D status requires <

10,000 bushels/acre at $2-$2.50/bushel planted costs, or approximately $20,000 - $25,000 per acre.

• These are higher costs than paid by the Virginia repletion program but the latter include discount prices and a planting near the source material.

• Assume unlimited supply of shell - de novo application of 45,000 acres costs one billion dollars.

• Maintenance application of shell at 1,000 bushels/acre every ten years requires S10 million /year.

Lesson #3. Unattended oyster habitat goes away.

Question #3: Is restoration about biology or shell budgets.

Examine question #3: oysters or shell (or both?)

• Fisheries rebuilding is typically about R > M + F• Not so in oysters where R > F + M + “shell habitat”.• Habitat requires regular and sustained recruitment in addition to

regular and sustained mortality to balance loss processes.• Dead oysters (shells) decay. With enough decay the habitat

disappears - and restoration fails. • It is about BOTH oysters and shell habitat.

SHELL RESOURCES: JAMES RIVER 1996-2003……...

0.0

5.0

10.0

15.0

20.0

25.0

30.0

35.0

1996 1997 1998 1999 2000 2001 2002 2003

Year.....

HIGH DENSITY REEFSMEDIUM DENSITY REEFSLOW DENSITY REEFS

Lesson #4: Data on R, M, F and shell is basic.Question #4: What is the periodicity of recruitment and mortality, and are they related?

Age specific mortality, HIGH density reefs

0.00

0.10

0.20

0.30

0.40

0.50

0.60

0.70

0.80

0.90

1998 1999 2000 2001 2002 2003

year

age 2, HIGHage 3, HIGHage4, HIGH

Examine question #4: recruitment and mortality.REPLACEMENT RATIO V AGE SPECIFIC MORTALITY

MEDIUM: y = 0.1167Ln(x) + 0.6517

R2 = 0.6258

HIGH: y = 0.2063Ln(x) + 0.6705 , R 2 = 0.5647

0.00

0.20

0.40

0.60

0.80

1.00

0.00 0.50 1.00 1.50 2.00 2.50 3.00 3.50 4.00

REPLACEMENT RATIO

HIGH

MEDIUM

LOW

• There is a relationship between salinity, recruitment, disease related mortality and habitat maintenance (shell budgets) that serve to both reduce individual, longevity and truncate year class structure.

• Habitat or broodstock alone will not insure recruitment. The stock:habitat:recruitment balance must be understood for the system to be maintained or restored.

Lesson #5: “Restoration”of a commercial fishery is different.

This is also about shell budgets but these are one time investments and ARE NOT comparable to the restoration budget issues. This is about an economic return and the estimators to evaluate options are fluid.

Lesson #6: We should consider large scale aquaculture - but it has “issues”.“Cultural issues”, common property law, multi-user conflicts, 3D water column

use/ leasing (zoning of the shallow water zone), and trophic impacts.

Conclusions to the lesson• The oyster is both remarkable and unusual - even as a

bivalve (one adductor, no foot, makes its own habitat).• With that “unusual” label comes limitations of evolved life

history strategy (propensity to go locally extinct).• The current situation in the Chesapeake Bay has conspired

to provide a series of challenge to these limitations. • The “media” expectations are high, sometimes unfounded

and sometimes too high.• We must set both reasonable expectations for what we can

achieve, and be prepared to venture into unfamiliar and controversial territory if we are to succeed.