1. Getting a Grip on the Ecological Effects of the Oil Spill on Alabama’s Coastal Waters:Oysters as an Indicator Bill Walton Assistant Professor/Extension Specialist Auburn University & AL Cooperative Extension Chris Linder, chrislinder.com
2. Potential Ecological Impacts:A Partial Listing Direct Mortality Smothering, poisoning, loss of insulation, etc. Change in growth rates & reproductive patterns Changes in distribution of mobile organisms Indirect Physiological changes Reproductive changes, changes in growth rates, change in disease resistance Behavioral changes Food web changes Changes in community composition (some species up, some down, etc.) Habitat changes E.g., low oxygen zones
3. Factors Affecting the Impacts:Another Partial Listing Contaminant Type of oil Degree of weathering Amount of oil Duration of oil Manner of exposure Questions about dispersant Organisms Life stage Reproductive/physiological state Distribution Ability to move (or not) Credit: LaDon Swann
4. Where Do We Look for Impacts? Diagram of fate of oil spilled from Amoco Cadiz in France in 1979 (Marchand 1979 and Girin 2001)
6. Why Oysters as an Indicator Species? Sessile (= doesn’t move) adult life stage Filter and accumulate particles from water Subject of long-term studies National Oceanic & Atmospheric Administration’s (NOAA) Mussel Watch Program Important keystone species Subject of important commercial fishery
11. Oysters as Habitat Number of restoration projects within the state The Nature Conservancy, Dauphin Island Sea Lab, University of South Alabama, AL Marine Resources Division, Mobile Bay Oyster Gardening Program, Auburn University Shellfish Lab, etc. Focus on environmental benefits of oysters Water clarity, supply of oyster larvae, habitat creation, shoreline protection, etc.
12. Productive Oyster Reefs Oyster reefs in the Gulf of Mexico had recently been classified as in ‘fair condition’, in contrast to most other parts of the world where oyster reef habitat is in severe decline (Beck et al. 2009) Both public reefs and private leases Reliance on natural ‘set’
13. Cultching is a Common Practice Most harvested oysters are shucked before going to market Large quantities of shell are produced by shucking houses This shell is returned to the water to sustain reef habitat both for conservation and fisheries
14. Oysters as a Harvest In 2008, the U.S. eastern oyster industry (Crassostreavirginica) produced over 23 million pounds of oysters, valued at almost $82.5 million (NMFS). By volume, the Gulf of Mexico dominated the harvest, accounting for over 89% of the harvest By value, however, the Gulf of Mexico obtained only 73% of the total dollar value of the US harvest (NMFS) Credit: Jim Gossen
15. Primarily Commodity Market Focused on the commodity, shucked product market, the 5-year average value of Gulf of Mexico oysters is $2.88/pound, almost an order of magnitude lower than the 5-year average value of New England oysters (almost entirely aquacultured product intended for the premium, half-shell market) of $24.42/pound (NMFS)
16. Ups & Downs in Harvest Tremendous variation in salinity Too much freshwater can be fatal to oysters Too much saltwater favors oyster predators and diseases Siltation can smother oysters Variations in natural set Hurricanes
17. Effect on the Safety of Seafood First priority is to protect human heath; therefore, closures are aggressive and pro-active Testing has so far confirmed that the closure areas have been adequate Contaminants associated with oil spills are dangerous Concerns about use of dispersant Corexit
18. Effect on the Safety of Seafood Process for re-opening First, no signs (sheen, smell) of oil on water Second, sensory tests of different species of seafood By species and area Smelled raw, smelled cooked, tasted cooked Trained field screeners can detect down to 10 ppm, while trained experts can detect down to 0.5 ppm Finally, analytical chemical tests to look for contaminants, including polycyclic aromatic hydrocarbons (PAHs) Testing is being done for the presence of the components of Corexit
19. Effects on the Safety of Seafood Potential long-term closures Very possibly re-openings on species by species basis, possibly varying by region Long-term monitoring to evaluate risks of recontamination
20. Impacts on Consumer Confidence and Demand Again, this was an immediate effect of the DHOS Affected consumption of crawfish, which are not a marine species and raised well inshore Will consumers believe government tests that indicate that seafood is safe? Opportunity for the region to embrace a very high standard of safety and quality?
21. Monitoring of Biological Effects is Also Being Aggressively Pursued Natural Resource Damage Assessment Legal process to determine damages for litigation across the region Mussel Watch Program Historically, two sites in Alabama (Dog River & Cedar Point Reef) Large number of natural resource agencies, universities and conservation organizations have begun assessment programs
22. Potential Biological Effects: a Partial List Mortality To my knowledge, only mortalities of adult oysters observed to date have been attributed to freshwater diversions to keep oil away from shore in LA Changes in growth Reproductive impacts Change in resistance to disease Reduction in larval survival/settlement
24. Data Collection: Methods Hatchery-reared, single oysters are deployed for a 2 month duration. One cage per site, four 15-oyster replicates in each cage. Salinity and temperature are collected from deployment sites by way of data-loggers. Oyster shell metrics, weights and survival are recorded prior to and post deployment.
26. Average Change in Shell Metrics Variations among growth measurements were significantly different between sites
27. Study Plan Monitor oyster growth, survival and condition at field sites along AL coast Possibly expand to FL and MS Do these vary among sites? Analyze degree of contamination of tissues Possibly add sediment and water samples Do biological responses correlate with contamination? Conduct this seasonally for at least 3 years to document changes over time Do these responses change over time? May also be useful for determining the effects of efforts to prevent contamination Awaiting research permit
