VERTIMAR-2005
Symposium on Marine Accidental Oil Spills
Effect of a simulated oil spill on natural assemblages of marine
phytoplankton enclosed in microcosms
J. GONZÁLEZ1, M. ARANGUREN1, E. FERNÁNDEZ1, X.A.G. MORÁN2,
X.A. ÁLVAREZ-SALGADO3, F.G. FIGUEIRAS3 and M. NIETO-CID3
1
Departamento de Ecoloxía e Bioloxía Animal, Universidade de Vigo, Facultade de Ciencias, 36200, Vigo,
Spain
2 Instituto Español de Oceanografía. Centro Oceanográfico de Xixón. Camín de L’Arbeyal s/n. 33212
Xixón. Spain
3 CSIC, Instituto de Investigacións Mariñas, Eduardo Cabello 6, E-36208, Vigo, Spain.
ABSTRACT Two microcosms experiments were carried out to assess the effect of a simulated oil spill on the
species composition, biomass and photosynthetic activity of natural phytoplankton assemblages. Both photosynthetic
activity and phytoplankton biomass decreased after 24-48 h of exposure to the oil spill. Thereafter, these variables
progressively recovered values close to the control. A marked shift in phytoplankton species composition was also
observed throughout the experiments. The magnitude of the phytoplankton response to the oil spill differed between the
two communities assayed. An inverse relationship was found between the initial growth rate of the phytoplankton
community and the decline in phytoplankton biomass and activity after the addition of the oil soluble fraction.
1. INTRODUCTION
Current knowledge on the effect of oil spills on the taxonomic composition, biomass, size
structure and physiological activity of natural phytoplankton communities is still scarce. Several
investigations have focussed on the effect of single PAHs on cultured phytoplankton species
(e.g. Ostgaard et al., 1984). However, few studies addressed the response of natural
phytoplankton to episodic inputs of oil to the marine environment. Recently, attempts have been
conducted aiming to understand the impact of oil pollution on pelagic primary producers using
experimental mesocosms (Ohwada et al., 2003). In this study we examine the effect of
experimental oil spills on two different natural coastal phytoplankton assemblages enclosed in
microcosms.
2. RESULTS AND DISCUSSION
Two microcosms experiments were carried out with the aim of evaluating the effect of the oil
soluble fraction on a natural phytoplankton community. Nine borosilicate glass flasks (4 l of
capacity) were filled with surface water collected from the Ría de Vigo. Three of these flasks
were maintained as controls. Two experimental treatments, low and high oil concentration were
tested. Microcosms were maintained in a culture chamber, at 18ºC, an irradiance of 70 µE s-1
m-2 under a 14L:10D photoperiod.
Samples were drawn from the flasks to determine the concentration of Polycyclic Aromatic
Hydrocarbons (PAHs) by fluorescence, dissolved inorganic nutrient concentration,
phytoplankton species composition, size-fractionated (20, 2 and 0.2 µm) chlorophyll a
concentration, photochemical efficiency of photosystem II (Fv/Fm), and size-fractionated (20, 2
and 0.2 µm) primary production rates measured by the radiocarbon incorporation method. The
photosynthetic efficiency of the Photosystem II (PSII) was measured daily. The rest of variables
were measured at 0 h, 24 h, 72 h and 120 h after the addition of oil.
Initial concentrations of total polycyclic aromatic hydrocarbons were 60 µg PAHs/l and 30 µg
PAHs/l for the high and low concentration treatments respectively. These initial concentrations
decrease rapidly over the first 48 h after oil addition. At the end of the experiments, the
concentrations of PAHs were approximately half of the initial values.
In both experiments, a significant decrease was observed for all measured variables 24-48
h after the experimental (see figure 1). The magnitude of this negative effect was dependent on
the concentration of oil added. After the initial negative effect, all the measured variables
recovered their initial values. Thus, 120 h after the addition of oil, the magnitude of chlorophyll a
concentration, primary production and photosynthetic efficiency of the Photosystem II in the low
and high oil treatments did not differed significantly from those determined in the control
treatments.
VERTIMAR-2005
Chl a (µg/l)
Symposium on Marine Accidental Oil Spills
1.80
1.60
1.40
1.20
1.00
0.80
0.60
0.40
0.20
0.00
Experiment I
0h
24 h
72 h
120 h
72 h
120 h
Time
7.00
Chl a (µg/l)
6.00
Experiment II
5.00
4.00
3.00
2.00
1.00
0.00
0h
24 h
Time
Figure 1: Temporal evolution of chlorophyll a concentration in both experiments. White bars
represent chlorophyll a concentration at control microcosms, light grey at low oil concentration
microcosms and dark grey at high oil concentration microcosms.
Both phytoplankton size structure and picoplankton and microplankton taxonomic
composition changed dramatically at microcosms where oil was added.
REFERENCES
Ohwada, K., Nishimura, M., Wada, M., Nomura, H., Shibata, A., Okamoto, K., Toyoda, K.,
Yoshida, A., Takada, H., Yamada, M. (2003) Study of the effect of water-soluble fractions of
heavy-oil on coastal marine organisms using enclosed ecosystems, mesocosms. Marine
Pollution Bulletin 47:78-84.
Ostgaard, K., Eide, I., Jensen, A. Exposure of phytoplankton to Ekofisk crude oil. (1984) Marine
Environmental Research 11:183-200.