Exxon Valdez oil spill EVOS legacy Synthesis of

Exxon Valdez oil spill [EVOS] legacy: Synthesis of long-term ecosystem responses Riki Ott, Charles H. “Pete” Peterson & Stanley “Jeep” Rice

Theme: Chronic effects of decade-long contamination of key shoreline habitats and indirect interactions are important 1994 EVOS oil, Prince William Sound, AK

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

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

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)

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.

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

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

Persistence of oil • Asphalts high on shore - biologically inactive • Biologically available pockets in protected sites for >10 yrs – Under armor of mussel beds with relatively unweathered oil contaminating mussels at least into summer 1994 at study’s 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 study’s end

Is the oil still there? 2001 Survey Results: 91 sites with 9, 000 total pits - 53 sites with oil - 38 sites without oil N

Distribution of oil 12 years later Upper intertidal Tidal zone (m) Surface oil (# of pits) Subsurface oil (# of pits) + 4. 8 + 4. 3 + 3. 3 + 2. 8 + 2. 3 + 1. 8 37 56 58 60 40 29 5 28 69 91 123 117 Biological zone (lower intertidal) < 1 m Oil below sampling grid = Yes How far down = ?

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

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

Fucus % cover Red algae Indirect effects on rocky intertidal community unoiled 100 • Modest bloom of ephemeral algae in absence of Fucus competition and with low grazing 0 • Absent nearby canopy, Fucus spore arrival is limited and recruits desiccate 100 oiled & not cleaned high on shore • Opportunistic barnacle colonizes heavily 0 • Fucus colonizing barnacle tests is 100 oiled & cleaned uprooted • Fucus expansion into low shore inhibits red algae 0 1991 1992

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