Allan K. Fukuyama and Jonathan P. Houghton. Pentec Environmental, Inc. ... ABSTRACT: Field surveys were conducted throughout Prince William. Sound in the summers of 1990 through 1992 to evaluate recovery of infauna from the effects of ...
IMPACTS ON INTERTIDAL INFAUNA: EXXON VALDEZ OIL SPILL AND CLEANUP William B. Driskell 6536 20th Avenue NE Seattle, Washington 98115 Allan K. Fukuyama and Jonathan P. Houghton Pentec Environmental, Inc. 120 West Dayton Edmonds, Washington 98020 Dennis C. Lees Ogden Environmental and Energy Services Company, Inc. 5510 Morehouse Drive San Diego, California 92121 Gary Shigenaka and Alan J. Mearns National Oceanic and Atmospheric Administration 7600 Sand Point Way NE Seattle, Washington 98115 Although the detrimental effects of oil on infaunal animals are well known, 2 ' 3 ' 13 the potential effects of oil-removal treatments on infauna are not as well understood. This study was initiated primarily to document the recovery process but also to separate, if possible, the effects of oiling on infauna from the effects of hot-water, high pressure washing. The results presented here are part of a larger study (see J. P. Houghton et al. 6 and in this volume, and D. C. Lees et al. in this volume) funded by the National Oceanic and Atmospheric Administration (NOAA) with support from the Environmental Protection Agency, the U.S. Coast Guard, the Marine Spill Response Corporation, and the American Petroleum Institute.
ABSTRACT: Field surveys were conducted throughout Prince William Sound in the summers of 1990 through 1992 to evaluate recovery of infauna from the effects of oiling and shoreline cleaning treatments following the Exxon Valdez oil spill. Infauna were quantitatively sampled at mixed sandlgravellcobble beaches categorized into treatment groups according to their general degree of disturbance. • Category 1: unoiled reference sites • Category 2: oiled sites, not hot-water-washed • Category 3: oiled sites, "cleaned" with hot-water flushes Shoreline treatments applied in 1989 and 1990 had varied effects on intertidal infauna including organism displacement and burial, thermal stress, oil dispersion, and transformed beach morphology. These treatments resulted in significant reductions in infauna (total abundance and diversity, as well as densities ofpolychaetes, bivalves, and some crustaceans) at Category 3 beaches. In contrast, Category 2 beaches had a richer and more varied infauna than Category 3 beaches. Multivariate analyses indicate some trends in recovery: namely, a convergence by certain Category 2 sites toward the Outside Bay, Category 1 control site. PAH concentrations in 1990 also suggest that treatments acted to move some hydrocarbons downslope from the upper beach into the shallow subtidal. By 1991, PAH concentrations in the shallow subtidal were no longer at the high levels seen in 1990, but PAH levels at other elevations of Category 3 sites remained at about the same levels as in 1990.
Methods and materials Prince William Sound is a protected fjord system located on the southcentral coast of Alaska. The study sites were located throughout most of central and southern Prince William Sound (Figure 1). Beaches in the protected embayments or small coves in Prince William Sound are primarily composed of a mixture of gravel, sand, and silt ("mixed-soft") but may include cobbles and/or scattered boulders. These areas support a diverse infauna of polychaetes, crustaceans, and mollusks, as well as naticid snails and sea stars, both predators on clams. Hard- or soft-shell clams may also occur in high abundance in the low intertidal. A stratified random sampling design was used in 1990 and 1991 to assess infauna at 13 mixed sand/gravel/cobble beaches, including 10 that were oiled to varying degrees in 1989. The sites were categorized by treatment groups according to their general degree of disturbance. • Category 1: unoiled reference sites • Category 2: oiled sites, not treated • Category 3: oiled sites, "cleaned" with hot-water flushes Two general null hypotheses were formulated for testing.
The T/V Exxon Valdez ran aground on Bligh Reef on March 24, 1989. Over the next several weeks, much of the 10.8 million gallons of spilled North Slope oil was deposited on beaches in the southern and western portions of Prince William Sound, as well as on Gulf of Alaska beaches to the southwest. Beach cleanup activities began in the sound in May 1989 and continued with varying degrees of intensity throughout the summer, with some additional efforts at selected locations in 1990 and 1991. 1>4
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Figure 1. Prince William Sound study area and sampling locations
HQ1
Diversity, total abundance, or number of infaunal taxa in mixed-soft substrates do not differ significantly between site categories. 2 H0 Density of selected invertebrate species in mixed-soft substrates does not differ significantly between site categories. Sampling was stratified within two intertidal tidal elevations following Zeh, Houghton, and Lees; 17 but only the lower level data are presented here. Corers (10.7 cm diameter by 15 cm deep) were used to obtain samples from five permanently marked points randomly located along a 30 m horizontal beach transect. The five samples from each site were field sieved through a 1.0 mm screen and preserved in 10 percent formalin. An additional sample was taken for grain size analysis. The samples collected in 1992 are currently being analyzed and are not reported here. At lower elevations, up to four additional randomly located 0.25 m2 quadrats were excavated and hand sorted to collect the larger bivalves. This method has been found to provide more efficient quantitative sampling of larger hard-shell clams than methods employing screens. 5 Butter and littleneck clams (Saxidomus giganteus and Protothaca staminea) larger than 5 mm were retained and frozen for length and age analyses in the laboratory. Whole sediment samples collected from mid transect at 11 lower elevation mixed-soft sites in July 1991 were analyzed for grain size distribution using a wet-sieve/volume-displacement technique. 10 Composite samples for sediment chemistry were taken at each sampling elevation, using standard hydrocarbon collection techniques to avoid sample contamination, and frozen for analysis of PAH content. At most sites, the chemistry sample was composited from surface sediments scooped approximately 3 cm deep at five locations immediately adjacent to the locations of the five infaunal cores. Sediment hydrocarbon analyses were performed at the Institute for Environmental Studies, Louisiana State University, Baton Rouge, Louisiana.
Statistical analyses. Typical of constrained sampling plans, the infauna sampling design has its own strengths and weaknesses. The design was established to allow monitoring of long-term recovery trends at specific sites; it is also well suited (by the number of replicated samplings at each site) for comparisons of oiling/treatment effects at specific points in time between sites. Because of the limited number of sites that could be sampled in each oiling/treatment category, however, it is less well suited to inference regarding the generalized impacts of oiling and treatment over all sites with similar history. Various metrics were applied to describe the data quantitatively (number of species, S; number of individuals, N; Shannon-Weiner species diversity, H') and to evaluate the significance of the findings. Nonparametric tests, randomization analyses of variance (ANOVAs), and t-tests were used to evaluate the significance of differences observed between site categories. Principal components analysis (PCA), a multivariate ordination technique, was used for tracking site recovery trends (details in Houghton et al. 6 ).
Results Sediment hydrocarbons. Total PAH concentrations were lower by at least an order of magnitude at Category 1 elevations than at Category 2 or Category 3 elevations (Table 1). In 1990, the average total PAH concentrations at the Category 2 sites were lower at the middle and shallow sub tidal elevations than at the Category 3 sites. The 1990 shallow subtidal Category 3 sites had the highest PAH values of all the elevations and categories. By 1991, concentrations were lower at all Category 2 elevations except at the lower elevation, but all Category 3 elevations remained at about the same levels as in the previous year except in the shallow subtidal, where there was a dramatic decrease in
FATE AND EFFECTS
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Table 1. Mean sediment PAH (ppm) from mixed-soft stations by category, 1990-1991 Category 1i Elevation
1990
Upper Middle Lower Shallow subtidal 1. 2. 3. 4.
0.0004 (n 0.0007 (n 0.002 (n 0.012 (n
± = ± = ± = ± =
0.0004 5) 0.001 4) 0.002 5) 0.006 2)
Category 3 3
Category 22 1991 4
4
0.0006 (n 0.0032 (n
± = ± =
0.0003 2) 0.0023 3)
1990 2.590 (n 1.624 (n 0.725 (n 0.448 (n
± = ± = ± = ± =
1991
5.6 8) 3.753 8) 1.91 11) 0.11 4)
0.068 (n = 1) 0.180 ± 0.22 (n = 4) 0.890 ± 1.50 (n = 6) 0.050 ± 0.05 (n = 4)
1990 0.994 (n 2.593 (n 0.07 (n 3.487 (n
± = ± = ± = ± =
1991
1.30 3) 5.454 7) 0.15 6) 3.01 3)
0.890 (n = 1) 2.400 ± 3.70 (n = 3) 0.050 ± 0.05 (n = 4) 0.200 ± 0.30 (n = 5)
Unoiled Oiled, untreated Oiled, treated Not analyzed Table 2. Regression equations for infauna parameters versus abiotic factors, lower mixed-soft intertidal stations
Year(s) 1991 1991 1991 1990, 1991 1990, 1991 1990, 1991 1991 1991
Dependent variablei N H' S N H' S Protothaca survival (%>--all stations Protothaca survival (%)- -Block Is.
Independent variable
Regression equation
fines (%) sands (%) sands (%) LnTPAH LnTPAH LnTPAH LnTPAH
N H' S N H' S Survival
= = = = = = =
621.1 fines - 52.2 2.57 - 4.55 sands 25.2 - 73.0 sands 85.3 - 9.28 LnTPAH 1.91 - 0.063 LnTPAH 13.8 - 0.879 LnTPAH 97.5 - 0.0225 LnTPAH
LnTPAH
Survival = 96.2 - 0.021 LnTPAH
r-squared (%) 36.9 55.2 34.2 45.6 28.4 32.3 83.0
P 0.05 0.01 0.06
