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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 • • • • • • • • • 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? • • • • • 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 Years 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 3 11 93 10 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 Estimated oyster growth in the James River using field observations and an oscillating Von Bertalanffy growth descriptor 10 0.00 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 2 3 4 5+ 100.0 80.0 60.0 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 • • • • • • 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 Cumulative mortality 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 challenge with successive years 5 0 1 2 3 4 5 Year class 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 larval period 20% loss per tidal exchange, 21 day larval period 9000 5000 4000 3000 2000 0.05 A B C D 40-50 la rval morta lity rate 0.07 0 0.25 E 50-60 50 recruitment: #/sq.m 6000 40 30-40 20-30 30 10-20 0-10 20 10 0.05 0.07 0 A B C popula tion structure popula tion structure 10 % loss pe r tidal exc hange, 2 5 day larva l pe riod 2500 2000-2500 1500-2000 1000-1500 500-1000 0-500 2000 recruitment: #/sq.m recruitment: #/sq.m 7000 1000 60 8000-9000 7000-8000 6000-7000 5000-6000 4000-5000 3000-4000 2000-3000 1000-2000 0-1000 8000 1500 1000 500 0.05 0.07 0 A B C popula tion structure D 0.25 E la rval morta lity rate D 0.25 E la rval morta lity 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% lo ss p er tidal e xchan ge, 21 day lar val p er iod 1 0% los s pe r tidal exc hange, 2 1 da y larval period 600 7000 6000-7000 5000-6000 500 5000 recruitment: #/sq .m 4000-5000 3000-4000 4000 2000-3000 1000-2000 3000 0-1000 2000 0.05 1000 lar val m o rtality r ate 0.07 0 A B C 0.25 D 500-600 400-500 400 300-400 200-300 300 100-200 0-100 200 100 0.05 0.07 0 A E B C po pulation str uctur e po pulation str uctur e 10 % loss per tidal exchange , 25 day la rval period 2000 recruitment: #/sq.m recruitment: #/sq .m 6000 1800 1600 1400 1200 1000 800 600 400 200 0 0.05 0.07 A B C po pulation str uctur e D 0.25 E 1800-2000 1600-1800 1400-1600 1200-1400 1000-1200 800-1000 600-800 400-600 200-400 0-200 lar val m o rtality r ate D 0.25 E lar val m o rtality r ate 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 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.