VERTIMAR-2005
Symposium on Marine Accidental Oil Spills
The effect of the Prestige oil spill on the phytoplankton in the
N-NW Spanish coast during spring
Manuel VARELA*1, Antonio BODE1, M Teresa ALVAREZ-OSSORIO1, Ricardo
ANADÓN2, Marcos LLOPE2 and Luis VALDÉS3
1
Instituto Español de Oceanografía. Muelle de Animas s/n. A Coruña. Spain
2 Laboratorio de Ecología. Universidad de Oviedo. Spain
3 Instituto Español de Oceanografía. Paseo del Arbeyal s/n. Gijón. Spain
ABSTRACT
Changes phytoplankton variables were studied during spring 2003, after the Prestige shipwreck, in
the N-NW Spanish coast using historical data available for the area. Some minor changes were occasionally observed,
but they did not show any clear pattern and were related to natural variability of the ecosystem. The phytoplankton
community structure did not change. The higher abundances of a few species were related to the high temperatures
measured during 2003 that resulted in an advance of summer-like conditions to spring. The lack of effects is discussed
in relation to the mechanisms removing fuel from surface waters to the sea floor. Zooplankton and diatoms play a key
role in removing both oil particles and emulsions form surface waters. Presently, it is not possible to determine even
some minor effects on plankton because the large variability of phytoplanktonic cycles.
1. INTRODUCTION
Traditionally, there have been two main approaches to study the effects of oil on plankton:
controlled laboratory conditions, and studies undertaken in natural conditions. The first
approaches yield a good idea on the potential toxicity on planktonic species but the conclusions
are often difficult to extrapolate to the natural environment. A more realistic approach is the in
situ study. However, this approach is often difficult due to the appropriate temporal and spatial
coverage, type of contaminants or characteristics of ecosystems. The response of plankton to
fuel is species specific and dependent of the environmental conditions. Besides, trophic
relationships among organisms can obscure the effects of contaminants (Johansson et al.,
1980).
The natural variability is the key factor to determine the effects of oil spills on plankton. The
variability of phytoplankton is especially marked in the N-NW Iberian Peninsula (Bode et al.,
2002) limiting our ability to differentiate anthropogenic from natural effects. A good knowledge of
this variability is essential for a correct evaluation of oil impact. In 1989 the Spanish Institute of
Oceanography (IEO) implemented the research core project Studies on Time Series of
Oceanographic Data. (Valdés et al., 2002) The data set obtained during the last years, allowed
for a quantification of the effects caused by the Prestige oil spill as relevant information on the
ecosystem variability is available. Additional information from opportunistic cruises (Pelacus,
core surveys from the IEO) and satellite data has been used likewise. The study has covered
the spring bloom the first important production period occurring at annual scale (Varela et al.,
2001) after the accident. This period coincides with the spawning of many species of high
commercial interest, so that any catastrophic impact on the first links of the pelagic food web
would result in failed or reduced recruitment.
2. RESULTS AND DISCUSSION
No detectable effects on phytoplankton were observed during spring 2003, after the
accident. The changes in chlorophyll were not noticeable as compared to previous years and
fitted to range variation of previous data. ANOVA showed no statistically significant differences
for both areas of study (Galicia and Asturias). Phytoplankton community structure showed minor
changes with only four species showing higher abundances after the spill. However, these
differences seem to be related to natural ecosystem variability as most of species of the spring
bloom do not change after the accident.
Large scale study in the whole NW-N Spanish coast carried out during Pelacus cruises in
spring from 2000 to 2003 showed not significant differences in chlorophyll concentration for
different areas of Galicia and Bay of Biscay after the accident as compared to previous years.
VERTIMAR-2005
Symposium on Marine Accidental Oil Spills


A Coruña shelf station chlorophyll
300
250
250
mg Chl a m-2



100

1993
2003
2002
2001
2000
1999
1998
1997
1996
1995
1994
1993
1992
1991
1990






0
0



2002
50

2001

2000


1999

1998

50



1997
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
150
1996

100
1995
150
200
2003
200
1994
mg Chl a m -2
Cudillero shelf station chlorophyll
300
Figure 1: Chlorophyll concentrations during spring before (white boxes) and after spill (2003, grey) in
Galicia and Asturias.
Dominant phytoplankton species were also similar. Sea-WiFS derived primary production for the
area in front of Rias Bajas from Galicia showed also not significant differences for the period
1998-2003

Satellite Primary Production
Integrated Chl a Pelacus Cruises
180
350
Bf: 00-02
160
She lf
250
120
100
80
gC m-2 y-1
-2
140
mg Chl a m
Oce an
300
Af: 03




60


40
200
150
100


50
20
0
0
SG Bf
SG Af
NG Bf
NG Af WB Bf WB Af
EB Bf
EB Af
1998-2002
2003
Figure 2: Chlorophyll for Pelacus Cruises before (Bf) and after the Prestige spill (Af) in the N-NW Spanish
coast. Derived satellite primary production for the area of Rias Bajas. SG: south Galicia, NG: north Galicia,
WB: Western Bay of Biscay, EB: Easter Bay of Biscay.
The lack or reduced effects are related to physical, chemical and biological factors. The high
dynamic of water masses favours the dispersion of oil and the transport of phytoplankton
populations from unaffected areas. The crude of Prestige had a low solubility and a low
concentration of aromatic hydrocarbons, the most toxic for plankton. On the other hand,
bacteria can degrade up to 60-80% of crude oil. Zooplankton is able to feed oil particles
(Johansson et al 1980), which are incorporated to faecal pellets and eventually sediment to sea
floor. In addition, vertical transport of oil emulsions can be conducted after adsorption to detritus
and living diatoms (Ohwada et al 2003), both abundant in the studied area. Therefore plankton
acts as biological pump removing from pelagic system, both, particulate and dissolved fuel. The
combination of these described effects favours the dispersion, degradation and sinking of fuel
reducing the effects and the fast recovery of possible losses in the pelagic system.
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Bode A., Varela M., Casas, B. and Gonzalez, N. (2002) Intrusions of eastern North Atlantic
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Johansson S., Larsson U., and Boehm, P. (1980) The Tsesis oil spill. Impact on the pelagic
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A., Takada H., Yamada M (2003) Study of the effect of water-soluble fractions of heavy-oil
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Coruña Ria) and its adjacent shelf (NW Spain). Continental Shelf Research, 21:1815-1838.