The Bahia las Minas Oil Spill

Volume 20/Number 8/August 1989 Marine Pollution Bulletin, Volume 20, No. 8, pp. 391-398, 1989. Printed in Great Britain.

0025-326X/89 $3.00+0.00 0 1989 Pergamon Press plc

The Bahia las Minas Oil Spill Hydrocarbon Uptake by Reef Building Corals KATHRYN A. BURNS and ANTHONY H. KNAP Bermuda Biological Station for Research hw., 17 Biological Station Lane, Bermuda GEO1

We report the analyses of hydrocarbons in the tissues of reef building corals, reef sediments and seawater samples collected in September 1986 as part of the initial impact assessment of a major oil spill in Panama. The patterns of gas chromatograms indicated the oil residues were highly modified in comparison with the oil spilled only 5 months before: volatile fractions and predominant n-aikanes were missing. Oil levels in corals from the heavily oiled areas were 25-50 mg g-t lipid as measured by UV fluorescence, while corals in control sites showed nearly non-detectable levels (0.1 mg g-l). Oil concentrations correlated with coral mortality rates as measured by decrease in area coverage. Concentrations of petroleum hydrocarons in reef sediments were also elevated in areas of high oiling (393 ~tg g-i dry wt) compared to control areas (0.1 gg g-t). High concentrations of oil in seawater surrounding the contiguous mangroves (5-29 p.g I-I) imply that leaching of oil from heavily oiled sediments will provide a source of contamination to the coral communities for an unknown time in the future. Modifications in the protein/lipid ratios of coral tissues were evident in these preliminary data indicating that oiling affected the lipid biochemistry of the surviving corals.

In April 1986 more than 50 000 barrels of mediumweight crude oil spilled from a ruptured storage tank into a complex region of mangroves, seagrasses and coral reefs on the Caribbean coast of Panama just east of the entrance to the Panama Canal. This spill, which is the largest recorded into coastal habitats in the tropical Americas, happened close to the Smithsonian Tropical Research Institute's marine laboratory at Galeta. As populations of plants and animals in both oiled and unoiled areas had been previously documented, the study of this spill affords a unique opportunity to assess the effects of oil on tropical coastal ecosystems. Investigations were begun immediately and initial ecological effects were summarized by Jackson et al. (1989). Intertidal mangroves, seagrasses, algae and associated invertebrates were covered by oil and died soon after. There was also extensive mortality of subtidal reef corals and infauna of seagrass beds. These dramatic effects stand in sharp contrast to conclusions based on

laboratory dosing experiments and small-scale field experiments which indicated that corals suffer only transient physiological effects and should not be expected to exhibit mortality associated with oil spills unless the oil is dispersed into subsurface waters (Knap, 1987; Ballou et aL, 1987). Small amounts of dispersants were sprayed from aircraft over offshore areas and in restricted channels. Cubit et al. (1987) reported that refinery officials estimated less than 21 000 1. of Corexit 9527 were used. This amount of dispersant and the limited areas over which it was sprayed, would have been inadequate to disperse the large amount of oil spilled. Thus chemical dispersion would not account for the mortality seen in subtidal corals over the extended areas documented in the study of this spill. In this report we present preliminary analyses of hydrocarbons in coral tissues, reef sediments and seawater samples collected in September 1986 as part of the initial impact assessment of this oil spill. Methods Sampling sites The coastline is convoluted, with strips of beach bordering exposed areas and mangroves lining sheltered areas. Offshore, there are subtidal seagrass beds with coral reefs to seaward. A photograph of the affected coastline and a map of the study area are given by Jackson et al. (1989). Samples of coral and associated sediments were collected from reefs undergoing intensive biological observations of growth and mortality. Samples were taken from the same reefs, close to, but just outside the areas marked for assessment studies. Palina West is an unoiled control reef in a relatively pristine area of the coast approximately 40 km northeast of the spill site. No oil from this spill was seen along this coast during the spill, but frequent shipping traffic to and from the Panama Canal is an occasional source of tar balls and other contamination. Naranjos South is located about 18 km upwind of the site of the spill and was visually categorized as moderately oiled. Sediments in pockets on these two reefs were coarse coral rubble, indicating high-energy sorting despite the relatively close proximity of seagrass beds in the landward direction. Galeta Channel, about 20 km downwind of the spill site, and Payardi North, at the spill site, were heavily oiled. Their associated sediments con391

Marine Pollution Bulletin

tained a large portion of small particles indicating they retained more of the fine sediments eroded from seagrass and mangrove areas landward. No oil slicks were observed on the days corals were collected, although on other occasions slicks were observed to emanate from highly polluted mangrove areas due to runoff during heavy rains.

Collections Siderastrea siderea is a common massive coral while Agaricia tenuifolia forms thin plate-like colonies which project from the reef surface. Samples of these scleractinian corals were collected from the reefs by a diver at 3-6 m depth using hammer and chisel. Each piece was brought to the surface, using care not to touch the living portions. The corals were sealed in solvent-washed aluminum foil. Surface sediments were collected by the diver using solvent cleaned glass jars as scoops. These were sealed with screw cap lids lined with foil. High-volume seawater samples were taken in areas of mangroves just west of Payardi North (Largo Remo North) and at Galeta Channel by passing water through a glass column packed with Amberlite XAD-2 resin. Columns were attached to mangrove roots with the intakes positione d below the estimated low tide mark. Sampling took approximately 5 h at flow rates of 150-400 ml min -1 over the bed volumes of 100 ml resin. Upon retrieval, columns were sealed with glass caps and wrapped in foil. Samples were transported on ice to the laboratory at Galeta where all but the water samples were frozen at -20°C. Coral and sediment samples and the refrigerated water sample columns were packed in ice chests and flown to the Bermuda Biological Station for Research for chemical analysis.

Analysis Corals were thawed and tissue was blown off the coral skeleton with compressed air into clean glass beakers (Knap & Sleeter, 1984). (This technique removes most of the coral tissue of these species, but we have found in subsequent work on other species that scraping coral surfaces with stainless steel scalpels increases tissue recovery.) Enough pieces of S. siderea were available for triplicate analysis whereas the A. tenuifolia had to be processed as single composite samples from each station. Because fragments of coral skeleton were included in the samples, it was not possible to determine an accurate wet weight of the tissues. Tissues were ground with precombusted NazSO4 into a homogeneous paste. Protein determinations were made on aliquots of the sample paste as a measure of tissue mass using the Folin-phenol procedure (Lowry et aL, 1951). The procedure allowed enough dilution of the aliquots to preclude any interference of the Na2SO 4 in the protein assays as determined by including the same amount of salt in the standards and blanks. Sediment samples were thawed, large rocks and plant matter were removed and the samples were spooned into a 500 ml round bottom flask and extracted for 8 h using a hydrolysis reflux procedure with NaOH/MeOH as the extraction solvent (UNESCO, 1982). Extracts were separated into non-saponifiable (NSL) and saponifiable (SL) lipid 392

fractions, dried with NazSO 4, and concentrated to 1 ml by rotary evaporation. Total extractable lipid determinations were made by evaporating 10 gl aliquots of the extracts onto the pan of a microbalance. Elemental sulphur was removed from sediment extracts by percolating them over a small column of activated copper. Water samples were extracted in a specially designed continuous extractor using acetone with 10% water (Ehrhardt, 1987). Total lipid extracts from the water samples and the NSL extracts from sediments and corals were separated into 'saturated' and 'unsaturated' hydrocarbon fractions by adsorption chromatography using alumina and silica gels (Bums & Smith, 1982). Hydrocarbons were analysed by capillary gas chromatography (GC) with flame ionization detection on SE 52 fused silica columns with H 2 carrier gas. N-octadecene was added to extracts as an internal GC quantification standard. Compounds resolving into single peaks were quantified by means of response factors calculated from external standards over the GC elution range of C~2 through C34 and naphthalene through picene. Unresolved components, typical of petroleum residues, were quantified by determining the GC areas gravimetrically and relating them to an average response factor over the appropriate elution range. Aromatic fractions were also analysed by ultraviolet fluorescence (UVF) using hexane dilutions of samples of the spilled oil to generate the standard response curve. Extracts were made up to appropriate dilutions to be read on the linear range of fluorescence emission versus concentration at 310 nm-360 nm for the excitation and emission monochromators respectively (UNESCO, 1984). Further compositional detail was obtained by coupled excitation-emission spectra with wavelengths set 23 nm apart (Burns & Smith, 1977). After extraction of the lipids, residual sediments were dried at 90°C and sieved to determine the size distribution of particles. Sieves were stainless steel of standard mesh sizes 63, 125,250,500, and 1000 pan.

Results Quantitative Results of triplicate analysis of the S. siderea corals are shown in Table 1. These triplicates establish the expected means and standard deviation for the field samples which were collected over an area of several tens of square metres at depths ranging 3-6 m. Horizontal bars break the data into statistically different groups based on one way analysis of variance using group means and a 95% confidence limit. The data includes two estimates for the content of 'petroleum' hydrocarbons in samples. These are the amount of unresolved compounds (URE) as determined by GC and the UVF oil equivalents of the aromatic fractions. The GC estimates expressed as mg URE g-i protein break the data into two groups: low and high pollution areas; while the same data expresed as mg URE g-i lipid break the data into low, medium and high contamination areas. The UVF oil equivalents g-I lipid break the data into unoiled, low, medium and high contamination areas. In all cases the relative ranking of contami-

Volume 20/Number 8/August 1989 TABLE 1

Concentrations of hydrocarbons in Siderastrea siderea. Biogenics* mg g-t lipid

Saturates URE t mg g-~ lipid

URE t mg g-~ protein

Palina West

1.4 0.3 0.2

1.8 0.6 0.6

0.40 0.11 0.15

0.2 >0.1 >0.1

2.8 1.8 0.2

Norangos

2.4 0.6 0.6

1.6 1.2 1.3

0.30 0.29 0.40

1.8 0.9 1.0

2.5 0.5 0.6

Galeta Channel

3.8 2.1 1.5

2.6 2.5 2.5

0.82 0.58 0.71

5.8 4.4 2.7

2.5 2.6 1.9

Payardi West

2.8 3.8 3.3

4.6 3.9 6.8

0.72 0.93 0.63

23.6 21.3 41.4

2.8 4.0 4.3

Reef

Unsaturates U V F oil* mg g-~ lipid

UREt mg g-~ lipid

*Biogenics are the sum of multiple peaks with RRI near 1500, 1700, and 1900 which are common biogenic hydrocarbons produced by marine algae. tURE is the GC signal generated by the complex mixture of hydrocarbon residues which cannot be resolved into individual peaks. This is a conservative estimate of 'petroleum' hydrocarbons in samples. *UVF oil units were determined against a standard curve made of the originally spilled oil. TABLE 2

Concentrations of petroleum hydrocarbons expressed as mg URE g-a lipid and mg g-~ protein, protein to lipid ratios, and overall assessment of severity of reef oiling based on tissue analysis of reef building corals. URE mg g-J lipid

URE mg g-~ protein

Palina West Siderastrea Agaricia

1.0 O.3

0.2 O.1

Naranjos South Siderastrea Agaricia

1.4 0.4

Galeta Channel Siderastrea Agaricia Payardi North Siderastrea Agaricia

Reefs

UVF mg g-~ lipid

Protein/ Lipid

Oiling severity

0.1 > O.1

4.6 2.5

none

0.3 0.1

1.3 0.4

4.3 2.6

lightmoderate

2.5 2.8

0.7 1.0

5.0 3.1

4.2 4.5

moderate -heavy

5.1 8.3

0.8 1.2

25.3 49.7

6.1 6.4

very heavy

TABLE 3

Hydrocarbons in surface sediments collected from coral reefs in the Bahia las Minas oil spill area and a control site plus associated physical composition data. wet/dry

lag Lipid/ g dry wt

% size composition*

Palina West

1.4

101

77/22/1/0.1/0/0

1

0.9

< 1

0.2

0.1

Naranjos South

1.4

133

52/44/3/0.2/0.1/0

4

0.4

2

0.5

2.7

Galeta Channel

2.2

603

13/8/25/37/12/5

85

nd

48

6.4

393

Payardi North

1.6

526

49/10/18/16/4/2

110

nd

53

0.2

343

Reef

Saturates t URE Biogenics

Unsaturates t URE Biogenics

UVF*

*Size composition determined by seiving the residue left after N a O H - M e O H extraction of 100 g wet sediment. Size fractions are: > 1 m m / > 500 ~tm/>250 ~tm/> 125 ~tm/>63 lain/