Exxon%20Valdez%20oil%20spill%20[EVOS]%20legacy:%20Synthesis%20of%20long-term%20ecosystem%20responses

1
Exxon Valdez oil spill EVOS legacy Synthesis
of long-term ecosystem responses

• Riki Ott, Charles H. Pete Peterson Stanley
  Jeep Rice

2
Theme Chronic effects of decade-long
contamination of key shoreline habitats and
indirect interactions are important
1994 EVOS oil, Prince William Sound, AK
3
Delayed, chronic, and indirect effects of
shoreline oiling/treatment

• Treat EVOS as an ecosystem perturbation
• Capitalize on vast research effort
• Synthesis focused on shoreline habitats
• Contrast of NRDA based on old ecotoxicity risk
  models vs. field-based sampling

4
Assumptions about oil toxicology in 1989

• Alaska's Water Quality Standard for PAHs was 10
  ppb and provided conservative protection of
  natural resources
• Oil toxicity declined very rapidly in a matter of
  days/weeks
• Acute toxicity tests of lab animals adequately
  predicted risk
• Contact with feathers and fur was the only
  significant route of injury to birds and mammals
• Oil spill impacts could be assessed on a
  species-by-species basis with no regard for
  dependencies within the ecosystem

5
Contrasting terms

• Acute vs. Chronic exposure
  ( short- vs. long-term)
• Lethal vs. Sublethal impacts
  ( mortality vs. growth,
  reproduction, body condition)
• Immediate vs. Delayed response
  ( rapid vs. postponed)
• Direct vs. Indirect effect
  ( A ? B vs. A ? C ?
  B)
• Trophic cascade vs. Biogenic habitat loss
  ( change in predator affects its
  prey, which affects its prey, etc. vs. change in
  an organism that provides structural living space
  for other organisms)

6
Benefits of EVOS field sampling approach

• Employs statistical sampling design
• Integrates responses across all mechanisms
• Includes chronic effects on long time scales
• Includes interactions of oil and other stressors
• Includes indirect interactions from trophic
  cascades, habitat modifications, etc.

7
Synthesis of long-term ecosystem responses

• Shows old assumptions of oil ecotoxicity to be
  inadequate
• Weathered oil persists
• Weathered oil remains bioavailable in important
  environments
• Weathered oil (multi-ring PAHs) induces toxicity
  during chronic exposure

8
Water column PAH contamination after EVOS

• Low (1-8 ppb) even
  during weeks 1-5 in
  1989
• Essentially below
  detection by end of
  summer 1989 using
  traditional water sampling
• But filter-feeding mussels revealed exposure and
  bioavailability even into summer 1992 via
  filtration of contaminated particulates

9
Persistence of oil

• Asphalts high on shore - biologically inactive
• Biologically available pockets in protected sites
  for gt10 yrs
• Under armor of mussel beds with relatively
  unweathered oil contaminating mussels at least
  into summer 1994 at studys end
• In groundwater of deltas of anadromous streams
  yrs later
• In sediments among boulders on oiled beaches for
  yrs
• Transported on particles to shallow subtidal
  where elevated PAHs persisted until 1995 at
  studys end

10
Is the oil still there? 2001 Survey
Results 91 sites with 9,000 total
pits - 53 sites with oil - 38 sites
without oil
11
Distribution of oil 12 years later
Tidal zone (m) 4.8 4.3 3.3 2.8 2.3
1.8 lt 1m
Surface oil ( of pits) 37 56 58 60 40 29
Subsurface oil ( of pits)
Upper intertidal
5 28 69 91 123 117
Biological zone (lower intertidal)
Oil below sampling grid Yes How far down ?
12
Shoreline treatments

• Intense in 1989, 1990 summers with some extending
  into 1991
• Invasive including wiping surfaces, pressurized
  washes with hot and cold water, bioremediation,
  rock washing, tilling, and berm relocation
• Had major impacts on shoreline habitat, plants
  and animals

13
Direct effects on rocky intertidal species

• Fucus removal - high and mid shore
• Limpet Tectura persona decline high on shore
• Balanoid barnacle decline
• Blue mussel decline
• Periwinkle Littorina sitkana decline
• Drilling predator Nucella lamellosa decline
• Main cause - pressurized washing

14
Indirect effects on rocky intertidal community
unoiled

• Modest bloom of ephemeral algae in absence of
  Fucus competition and with low grazing
• Absent nearby canopy, Fucus spore arrival is
  limited and recruits desiccate high on shore
• Opportunistic barnacle colonizes heavily
• Fucus colonizing barnacle tests is uprooted
• Fucus expansion into low shore inhibits red algae

Red algae
oiled not cleaned
cover
oiled cleaned
100
Fucus
0
1990 1991 1992
15
Possible indirect effects on rocky intertidal

• Potential induction of unstable cycle in Fucus
  cover as single-aged colonist plants senesce in
  synchrony 5 yrs later
• Reduction of biogenic habitat normally provided
  by Fucus and blue mussels impacts gastropods and
  smaller invertebrates