Effects of the “Amoco Cadiz ” oil spill on an eelgrass community at roscoff (france) with special reference to the mobile benthic fauna

HELGOJ.~qDER MEERESUNTERSUCHUNGEN Helgol~inder Meeresunters. 33, 182-191 (1980)

Effects of the " A m o c o Cadiz" oil spill on an e e l g r a s s

c o m m u n i t y at Roscoff (France) with s p e c i a l r e f e r e n c e to

the m o b i l e benthic fauna

C. den Hartog & R. P. W. M. Jacobs

Laboratory of Aquatic Ecology, Catholic University; Toernooiveld, 6525 t~D Nijmegen, The Netherlands

ABSTRACT: In October 1977 an investigation w a s initiated of the qualitative a n d quantitative composition of the fauna of the eelgrass (Zostera marina) b e d s at Roscoff. Samples w e r e t a k e n in 2 seagrass b e d s at different tidal levels in order to follow numerical c h a n g e s in the course of the year. In March 1978 the area of study w a s struck b y the oil slick of the tanker "Amoco Cadiz". For this reason s a m p l i n g has b e e n c o n t i n u e d at the same frequency. The t a b u l a t e d results show d e a f l y that the oil slick h a d a profound but selective influence on the various animal groups; some of t h e m d i s a p p e a r e d w h i l e others w e r e a p p a r e n t l y unaffected. Rapid recovery of some species has t a k e n place, but r e - e s t a b l i s h m e n t of other species, particularly the filter f e e d e r s has not b e e n observed. The very diverse a m p h i p o d fauna has d i s a p p e a r e d , a n d has b e e n r e p l a c e d by a population of Pherusa fucicola a n d Garnmarus locusta; the latter was a b s e n t in the year before the oil disaster took place.

I N T R O D U C T I O N

Since the beginning of 1976 an ecological study of structural and functional aspects

of the eelgrass communities in the surroundings of Roscoff (France) has been in progress.

F r o m February 1976 to February 1977 the productivity, the biomass fluctuations, and the

growth pattern of the dominant species, Zostera marina L, have been studied (Jacobs,

1979). Furthermore the epiphytic algae, including the diatoms, on Zostera were

examined with special emphasis on their colonization patterns, and their dependence on

the rhythm of leaf production and leaf shedding of the host plant. A quantitative study of

the macrofauna w a s started in M a y 1977.

Unfortunately, in M a r c h 1978, this ecological p r o g r a m m e was drastically disturbed

by the stranding of the tanker " A m o c o Cadiz" which released its cargo of 216 000 tons of

crude oil and 4000 tons of bunker fuel and thereby polluted a considerable stretch of the

coastline of northern Brittany.

O n 20 M a r c h the oil slick reached the surroundings of Roscoff and c.overed our study

area. As w e were in the position to m a k e a comparison with the original situation, w e

decided to continue the sampling programme, although with a changed objective, viz.

the effect of the oil spill on the Zostera community.

This paper deals with the preliminary results of this study, with respect to the mobile

invertebrates. T h e benthic infauna results are discussed by Jacobs (1980).

Effects of oil spill 183

STUDY AREA

Eelgrass b e d s are a p r o m i n e n t f e a t u r e i n the coastal a r e a of Roscoff. T h e y cover 12.Y k m 2 of w h i c h almost 80 % is s i t u a t e d a b o v e the m e a n low w a t e r m a r k at s p r i n g tide (MLWS). T h e u p p e r l i m i t of the e e l g r a s s b e d s c o i n c i d e s more or less w i t h the m e a n low w a t e r m a r k at n e a p tide (MLWN}. t n the s u b l i t t o r a l

Zostera marina

d e s c e n d s to ca. 4 m b e l o w MLWS (Jacobs, 1979}.

T h e history of t h e e e l g r a s s b e d s of the Roscoff area is r e a s o n a b l y w e l l k n o w n ; t h e y w e r e m a p p e d b y Pruvot (1897), J o u b i n {1909}, a n d later b y Blois et al. {1961} a n d J a c o b s {1979); a d e t a i l e d report w a s p r e s e n t e d b y De B e a u c h a m p (1914). More d e t a i l e d observa- tions o n the

Zostera

b e d s c a n b e f o u n d scattered i n the e x t e n s i v e l i t e r a t u r e o n t h e Roscoff a r e a .

T h e s t u d y of the f a u n a of the eelgrass c o m m u n i t y w a s c o n c e n t r a t e d i n two h o m o g e n e o u s beds, o n e s i t u a t e d just b e l o w t h e l e v e l of MLWN, a n d the other approxi- m a t e l y 0.5 m lower. T h e former w a s c h a r a c t e r i z e d b y r e l a t i v e l y m a n y

Zostera

shoots (700-800 p e r m 2) w h i c h w e r e n o t l o n g e r t h a n 30 cm. T h e r h i z o m e m a t w a s ca. 9 cm thick, a n d t h e r e w a s n o m a t of l o o s e - l y i n g algae. This b e d b e c a m e e x p o s e d d u r i n g almost e v e r y low w a t e r period.

T h e l o w e r eelgrass b e d w a s c h a r a c t e r i z e d b y fewer b u t l o n g e r shoots (500-600 p e r m2; u p to 50 cm long) T h e r h i z o m e m a t w a s ca. 6 c m thick. This b e d w a s s i t u a t e d i n a n e n o r m o u s t i d a l pool t h a t r e t a i n e d a few c e n t i m e t r e s of w a t e r d u r i n g e a c h low w a t e r period. B e t w e e n the shoots a m a t of e n t a n g l e d , l o o s e - l y i n g a l g a e w a s present~ it c o n s i s t e d m a i n l y of

Coralllna officinalis L., Cladostephus spongiosus

(Huds.) C. Ag. a n d

Sphacelaria

species.

I n this p a p e r o n l y t h e r e s u l t s o b t a i n e d from t h e l o w littoral e e l g r a s s b e d w i l l b e discussed. I n the other b e d the n a t u r a l process of s a n d i n g - u p , c a u s i n g a d e c r e a s e i n s p e c i e s a n d i n d i v i d u a l s , i n t e r f e r e d w i t h the effect of the oil pollution, a n d the d a t a could b e e a s i l y m i s i n t e r p r e t e d .

M E T H O D S

A l t h o u g h the s t u d y of the f a u n a of the e e l g r a s s b e d w a s b e g u n i n M a y 1977, t h e first m o n t h s w e r e d e v o t e d to i d e n t i f i c a t i o n of species, i m p r o v i n g t h e s a m p l i n g t e c h n i q u e , a n d s e l e c t i n g the most r e p r e s e n t a t i v e sites. T h e data o b t a i n e d i n the p e r i o d M a y - S e p - t e m b e r 1977 h a v e n o t b e e n u s e d i n t h e p r e s e n t analysis.

From O c t o b e r 1977 u n t i l April 1979 a b o t t o m s a m p l e of 20 X 20 c m 2 w a s t a k e n m o n t h l y i n t h e h i g h a n d i n t h e l o w littoral e e l g r a s s beds. T h e s e s a m p l e s w e r e s i e v e d (1- m m m e s h size) a n d all i n d i v i d u a l s w e r e collected, p r e s e r v e d a n d i d e n t i f i e d . T h e s a m p l e size c h o s e n w a s i n fact a compromise. For the s m a l l e r species it w a s more t h a n sufficient, for some l a r g e r s p e c i e s p r o b a b l y too small. A l a r g e r s a m p l e size, however, w o u l d h a v e i n c r e a s e d the w o r k to such a d e g r e e that its e x e c u t i o n w o u l d h a v e b e e n i m p o s s i b l e w i t h i n a r e a s o n a b l e time.

F~

a~

Table

1.

General

data

of

the

fauna

in

the

low

littoral

Zostera

marina

bed

at

Roscoff

(numbers

per

400

cm

2)

Parameters

1977

1978

O

N

D

J

F

M

A

M

J

J

A

S

O

N

D

1979

J

F

M

A

Number

of

individuals

N

540

899

577

Number

of

species

S

48

46

47

Diversity

index

H'

2.49

2.58

2.47

Evenness

J

0.64

0.67

0.64

566

1162

802

393

101

222

115

133

194

214

444

395

255

439

529

686

49

73

70

39

26

37

22

30

30

28

26

33

31

51

56

44

2.66

2.71

2.62

2.28

2.64

2.55

2.46

2.85

2.45

2.37

1.86

1.98

2.36

2.79

2.67

2.01

0.68

0.63

0.62

0.62

0.81

0.71

0.80

0.84

0.72

0.71

0.57

0.56

0.69

0.71

0.66

0.53

Table 3. Amphipoda in the low littoral Zostera bed at Roscoff, before and after the oil spill of the "Amoco Cadiz" (numbers per 400 cm 2) Species 1977 1978 1979 O N D J F M A M J J A S O N D J F M A Pherusa fucicola Leach 9 4 1 64 58 3 1 5 2 9 25 19 30 10 Stenothoe monoculoides (Montagu) 1 1 9 11 1 6 2 Harpinia pectinata O. Sars 3 1 1 13 7 2 1 Melita obtusata Montagu 3 3 1 1 Dexamine rhea Boeck 6 1 1 13 2 2 1 Ampefisca spinipes Boeck 1 2 1 Harpinia crenulata Boeck 1 5 11 2 Apherusa bispinosa (Bate) 2 Nototropis guttatus (A. Costa) 1 1 4 ~lasmopus rapax A. Costa 1 1 Dexamine spinosa (Montagu) 1 Aora typica Kr6yer 1 1 1 1 Lembos websteri Bate 3 5 6 3 26 9 Microprotopus longimanus Chevreux 2 3 Eurystheus maculatus (Johnston) 1 1 4 Amphithoe vaillanti Lucas 1 1 1 Amphithoe rubricata (Montagu) 4 1 Pleonexes gammaroides Bate 1 Sunamphithoe pelagica ,(Milne-Edwards) 1 1 1 Jassa falcata (Montagu) 1 1 1 1 2 Erichthonius brasiliensis (Dana) 2 Podocerus variegatus Leach 1 5 Coremapus versiculatus Norman 5 1 1 Phtisica marina Slabber 1 1 CapreHa sp. 2 5 Lysianassidae sp. 2 3 1 3 1 Gammarus locusta (L.) 8 13 1 3 Leucothoe spinicarpa (Abildgaard) 1 Leucothoe incisa D. Robertson 1 2 Apherusa jurinei (Milne-Edwards) 2 Number of individuals 25 28 16 16 160 120 5 3 8 5 2 10 39 31 37 12 Number of species 10 8 9 11 21 20 2 3 1 1 1 2 3 6 5 2

Table 4. Cumacea, Tanaidacea, Isopoda and Echinodermata in the low littoral Zostera bed at Roscoff, before and after the oil spill of the "Amoco Cadiz" (numbers per 400 cm 2) Species 1977 1978 1979 O N D J F M A M J J A S O N D J F M A

Cumacea Iphinoe

tenella G. O. Sars 10 11 7 30 21 1 13 8 11 7 Cumella pygmaea G. O. Sars 1 Bodotria scorpioides (Montagu) 1 - 2

Tanaidacea Apseudeslatreillei(Milne-Edwards)

203 190 100 51 353 278 56 6 10 6 5 42 68 238 214 91 113 117 337 Apseudes telpa (Montagu) 28 69 20 27 57 3 5 2 1 9 Leptochelia dubie Kr6yer 1 2 6 1 1

Isopoda Parenthure

costana Bate et Westwood 2 1 1 2 1 Dynamene bidentete (Adams) 1 1 1 Janira meculosa Leach 1 1 6 1 1 Idotea pelegica Leach 1 1 Astecille longicornis (Sowerby) 1 Munne minute Hansen 2 Idotea chelipes (Pallas) 1

Echinodermata Amphipholissquemate(Delle

Chiaje) 72 210 190 120 178 134 164 20 12 7 19 37 27 20 43 41 47 82 85 Asterina gibbose (Pennant) 1 Ophiure albide Forbes 1

188 C. d e n H a r t o g & R. P. W. M. J a c o b s

RESULTS

T h e e e l g r a s s itself r e m a i n e d a l m o s t u n a f f e c t e d b y t h e oil spill. A l t h o u g h d u r i n g t h e first w e e k s after t h e s p i l l m a n y p l a n t s h a d b l a c k " b u r n t " l e a v e s , t h e s e w e r e s h e d a c c o r d i n g to the p a t t e r n n o r m a l for t h e s p e c i e s . A p a r t from this s h o r t - t e r m effect no o t h e r d a m a g e w a s o b s e r v e d . T h e g e n e r a l s t r u c t u r e of t h e e e l g r a s s b e d s w a s not h a r m e d at all. C h a n g e s o b s e r v e d i n t h e f a u n a , therefore, c a n n o t b e a s c r i b e d to d a m a g e to t h e frame p l a n t of the c o m m u n i t y .

In T a b l e 1 t h e total n u m b e r s of s p e c i e s a n d i n d i v i d u a l s c o l l e c t e d m o n t h l y are p r e s e n t e d . It is o b v i o u s t h a t b o t h d e c r e a s e d after t h e oil spill, a d e c r e a s e w h i c h b e c a m e e v e n m o r e a p p a r e n t in M a y 1978. H o w e v e r , in the c o u r s e of 1978 t h e n u m b e r s of i n d i v i d u a l s i n c r e a s e d a g a i n , a l t h o u g h in s p r i n g 1979 t h e h i g h m a x i m a of t h e p r e c e d i n g s p r i n g w e r e not r e a c h e d . T h e n u m b e r of s p e c i e s r e m a i n e d c o n s i d e r a b l y l o w e r t h a n b e f o r e t h e oil spill.

T h e S h a n n o n - W i e n e r i n d e x v a l u e s for d i v e r s i t y

(H)

a n d e v e n n e s s

(J]

w e r e c a l c u -

l a t e d m o n t h l y . In t h e p e r i o d b e f o r e t h e oil s p i l l t h e s e w e r e r e a s o n a b l y constant, H r a n g i n g from 2.5 to 2.7 a n d J v a r y i n g b e t w e e n 0.62 a n d 0.68, i n d i c a t i n g a s t a b l e w e l l - b a l a n c e d c o m m u n i t y . A f t e r t h e oil s p i l l t h e f l u c t u a t i o n s of H w e r e b e t w e e n 2.0 a n d 2.8 a n d t h o s e of J b e t w e e n 0.53 a n d 0.84, i n d i c a t i n g a d i s t u r b e d b a l a n c e .

In T a b l e s 2 - 4 t h e d a t a of s o m e g r o u p s of m o b i l e a n i m a l s a r e p r e s e n t e d . D a t a on fish a n d d e c a p o d c r u s t a c e a n s h a v e not b e e n c o n s i d e r e d b e c a u s e t h e s a m p l i n g t e c h n i q u e w a s not a d e q u a t e for t h e s e groups.

G a s t r o p o d a

T h e G a s t r o p o d a w e r e l i t t l e a f f e c t e d b y t h e oil s p i l l ( T a b l e 2). M o s t of t h e m a r e b o u n d to t h e bottom; s o m e of t h e m c r a w l on t h e e e l g r a s s l e a v e s , b u t w h e n t h e t i d a l c u r r e n t s b e c o m e too s t r o n g t h e y u s u a l l y d r o p to t h e bottom, w h e r e t h e y r e m a i n u n t i l t h e n e x t l o w w a t e r p e r i o d .

F r o m T a b l e 2 it is o b v i o u s t h a t a l m o s t a l l s p e c i e s f o u n d b e f o r e t h e oil s p i l l w e r e f o u n d also l a t e r . T h e g r e a t e s t r i c h n e s s i n s p e c i e s w a s f o u n d in F e b r u a r y 1978 a n d in

M a r c h 1979. T h e m o s t n u m e r o u s s p e c i e s w a s

Cingula semicostata,

w i t h t h e h i g h e s t

n u m b e r of i n d i v i d u a l s in w i n t e r .

In g e n e r a l the n u m b e r of i n d i v i d u a l s a n d of s p e c i e s i n the w i n t e r of 1978 a n d 1979 a p p e a r e d to b e of t h e s a m e m a g n i t u d e . In 1978 t h e n u m b e r of s p e c i m e n s h a d a l r e a d y d r o p p e d c o n s i d e r a b l y b e f o r e the oil s p i l l t o o k p l a c e . S o m e s p e c i e s w e r e not f o u n d after t h e oil p o l l u t i o n t o o k p l a c e , a n d o t h e r s w e r e n o t s e e n after the s u m m e r of 1978. T h e s e species, h o w e v e r , w e r e not c o m m o n in e e l g r a s s ~ e d s , a n d t h e i r a b s e n c e is p r o b a b l y m e r e l y a c c i d e n t a l .

A m p h i p o d a

Effects of oil spill 189

t h e s u m m e r of 1978 a m p h i p o d s w e r e p r a c t i c a l l y a b s e n t , b u t i n the a u t u m n

Pherusa

[ucicola,

the s p e c i e s most a b u n d a n t before the oil spill, r e a p p e a r e d , f o l l o w e d b y

Gammarus locusta,

a u b i q u i s t formerly n o t o b s e r v e d i n this a m p h i p o d c o m m u n i t y ; a few i n d i v i d u a l s of a few other species w e r e found, b u t a recovery h a d n o t t a k e n p l a c e b y April 1979.

C u m a c e a

This g r o u p w a s i n fact r e p r e s e n t e d b y o n e f r e q u e n t species

Iphinoe tenella

(Table 4). In t h e p e r i o d N o v e m b e r 1 9 7 7 - M a r c h 1978 it w a s fairly a b u n d a n t ; after the oil spill only 1 s p e c i m e n w a s f o u n d i n A p r i l a n d since t h e n it w a s a b s e n t for 8 months. I n t h e w i n t e r of 1979 it r e a p p e a r e d i n n u m b e r s c o m p a r a b l e to those before t h e oil spill.

T a n a i d a c e a

Before the oil spill 3 species of T a n a i d a c e a w e r e present.

Apseudes latreillei,

w h i c h w a s b y far the c o m m o n e s t , s h o w e d a g r e a t d e c r e a s e i n n u m b e r s after the oil spill b u t r e c o v e r e d c o m p l e t e l y i n the f o l l o w i n g a u t u m n . T h e s e c o n d species,

A. talpa,

h a d d e c r e a s e d i n n u m b e r s before the oil spill; i n w i n t e r of 1979 a few i n d i v i d u a l s w e r e present. T h e d e c r e a s e i n n u m b e r s of t h e s e two species i n s p r i n g is a n a t u r a l p h e n o m e - non, a l t h o u g h the d e c r e a s e i n 1978 w a s more p r o n o u n c e d d u e to the oil pollution. T h e rarest species,

Leptochelia dubia,

w a s f o u n d o n l y once after t h e oil spill.

I s o p o d a

T h e n u m b e r of Isopoda i n the

Zostera

b e d w a s u s u a l l y v e r y low w i t h a slight i n c r e a s e i n w i n t e r . This g r o u p w a s also affected b y the oil slick.

Paranthura costana,

w h i c h w a s f o u n d also o n s e v e r a l occasions i n s p r i n g a n d s u m m e r 1977, w a s s e e n o n l y once after the oil disaster. For 8 m o n t h s n o t a s i n g l e isopod was s e e n ; i n the f o l l o w i n g w i n t e r o n l y 4 s p e c i m e n s , r e p r e s e n t i n g 4 species, w e r e collected. A l t h o u g h this g r o u p w a s n o t c o m m o n , t h e oil p o l l u t i o n c a u s e d a n o b s e r v a b l e r e d u c t i o n i n the n u m b e r s of species a n d i n d i v i d u a l s .

E c h i n o d e r m a t a

Amphipholis squamata

a p p e a r e d to b e c o m m o n i n t h e e e l g r a s s bed. R e m a r k a b l y , it d i d n o t d e c r e a s e directly after the oil spill, b u t a m o n t h later. T h e n u m b e r s r e m a i n e d low b u t i n c r e a s e d g r a d u a l l y t o w a r d s t h e e n d of the o b s e r v a t i o n period; the m a x i m a o b s e r v e d i n the w i n t e r 1977-1978 w e r e not reached.

DISCUSSION

190 C. d e n H a r t o g & R, P. W. M. J a c o b s

b e f o r e t h e oil spill. S o m e i n f l u e n c e of t h e oil spill on t h e I s o p o d a c o u l d b e d e t e c t e d , but as this g r o u p w a s n e v e r n u m e r o u s in t h e e e l g r a s s b e d u n d e r i n v e s t i g a t i o n , t h e result is not c o n v i n c i n g . T h e effect of t h e oil spill on t h e A m p h i p o d a , h o w e v e r , w a s s p e c t a c u l a r .

T h e s i t u a t i o n of t h e e e l g r a s s b e d s b e l o w the l e v e l of m e a n l o w w a t e r n e a p t i d e i m p l i e d that t h e contact b e t w e e n t h e oil slick a n d t h e e e l g r a s s l a s t e d o n l y for at m o s t 6 hours a day. D u r i n g this t i m e t h e f l a t - l y i n g e e l g r a s s l e a v e s f o r m e d a buffer b e t w e e n the oil s l i c k a n d t h e bottom. D u e to t h e firm r h i z o m e mat, m i x i n g of oil a n d s e d i m e n t w a s not p o s s i b l e in t h e e e l g r a s s bed. In fact o n l y t h e d i s s o l v e d fraction of the oil c o u l d p e n e t r a t e u n d e r t h e e e l g r a s s a n d in t h e i n t e r s t i t i a l ' w a t e r . This m a y e x p l a i n the fact that just t h e filter f e e d e r s s u c h as m o s t A m p h i p o d a a n d s o m e f a m i l i e s of P o l y c h a e t a (Jacobs, 1980) w e r e struck, w h i l e o t h e r g r o u p s of o r g a n i s m s r e m a i n e d r e l a t i v e l y u n a f f e c t e d .

T h e buffer effect of t h e e e l g r a s s also b e c o m e s e v i d e n t w h e n the n u m b e r s of oil v i c t i m s are c o m p a r e d w i t h those from o p e n b e a c h e s a n d s h e l t e r e d a r e a s w h e r e t h e r e w a s no c o v e r of e e l g r a s s , a n d w h e r e t h e b o t t o m a n d the oil c a m e into direct c o n t a c t (Hyland, 1978).

A s i m i l a r f u n c t i o n m a y h a v e b e e n f u l f i l l e d by t h e P u c a c e a e in t h e i n t e r t i d a l belt; h o w e v e r , d u e to t h e i r h i g h e r p o s i t i o n on the shore, t h e i r contact w i t h the oil w o u l d h a v e b e e n of l o n g e r duration, a n d t h e d e g r e e of p r o t e c t i o n of t h e o r g a n i s m s u n d e r the P u c a c e a e c o v e r m a y h a v e d e p e n d e d on t h e t h i c k n e s of that cover.

Prom t h e results o b t a i n e d it is a p p a r e n t that t h e effect of the oil spill on v a r i o u s a n i m a l g r o u p s w a s only a t e m p o r a r y d i s t u r b a n c e w h i c h c o u l d b e o v e r c o m e by the h i g h r e p r o d u c t i v e p o t e n t i a l of t h e survivors. In t h e c a s e of t h e A m p h i p o d a it c a n n o t b e p r e d i c t e d w h e t h e r t h e effect of t h e oil spill w i l l b e t e m p o r a r y or p e r m a n e n t b e c a u s e t h e y n u r s e t h e i r b r e e d and, t h e r e f o r e , h a v e a l o w r e p r o d u c t i v e p o t e n t i a l . T h e " A m o c o C a d i z " d i s a s t e r has a t t r a c t e d m u c h a t t e n t i o n b e c a u s e of the e n o r m o u s scale of t h e oil p o l l u t i o n it caused. Less s p e c t a c u l a r oil spills m a y c a u s e l o c a l l y s i m i l a r d a m a g e . T h e d a t a o b t a i n e d g i v e an i m p r e s s i o n of t h e i n f l u e n c e of an oil spill on a

Zostera

c o m m u n i t y in t h e e a r l y spring, just after t h e w i n t e r p e a k of a n u m b e r of littoral o r g a n i s m s , a n d b e f o r e t h e start of t h e r a p i d d e v e l o p m e n t of t h e e e l g r a s s . It is not c e r t a i n w h e t h e r t h e effect on the f a u n a w o u l d h a v e b e e n s i m i l a r h a d a spill o c c u r r e d in the s u m m e r .

Acknowledgements.

We would like to thank J. Stassen, W. Huisman, W. Buys, L. Pierson, N. Manders and T. de Jong, who provided practical assistance throughout this study. A great part of the practical work was carried out at the Station Biologique at Roscoff and we thank the director, Prof. Dr. J. Bergerard, and his staff for their hospitality. The identification of the representatives of the various crustacean groups has been checked by Dr. J. Dieleman. - The first part of this investigation (until April 1978) was made possible by financial support from the Netherlands Organization for the Advancement of Pure Research (ZWO) and the second part was financed by the Shell Internationale Research Maatschappij.

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E f f e c t s of o i l s p i l l 191

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