Indirect effects
Marine plants and animals do not live in isolation from each other. They
develop in an environment teeming with a wide variety of biological interaction.
This interaction goes from predator/prey relationships to situations of
dependence, symbiosis, parasitism and other situations in which an organism
or group of organisms provides a shelter or another necessity for one or
several species in the community.
Members of all the groups of organisms - algae, bacteria, invertebrates,
fish, birds, mammals – can be affected by an oil
spill. All damages caused by oil to individuals of a group may lead
to changes in the structure and functioning of the biological community.
Four broad types of indirect effects can be distinguished:
• death by starvation of organisms whose usual source of food is polluted,
and where alternative food supplies are not available
• disturbance of certain interactions between species, due to the
elimination or reduction of certain species
• large-scale proliferation of organisms which prey on the food usually
consumed by other species present in the environment
• modification of habitats due to the loss of key species, such as
seagrasses or mangroves, or the impacts of clean-up operations, such as
the alteration or disappearance of the substrate.
A reference condition of
vegetation on land (France)
In 2000-2002, the French National Botanical Conservatory in Brest
coordinated the development of a reference
condition for shoreline flora and fauna in Brittany and the Pays de
la Loire (France). This work came as a response to the need, which had become
apparent in the aftermath of the Erika oil spill, for a specialised tool
to provide information on the issues affecting vegetation, which could act
as a decision-making aid in the use of contingency
plans for marine pollution. This reference condition made use of previously
acquired knowledge and provided a diagnosis of the flora (species) and the
patrimonial shoreline vegetation (vegetation communities or habitats), with
a particular focus on formatting the information necessary for those responsible
for the fate of the natural heritage. To the information which was already
available was added an interpretation of aerial digital photos georeferenced
by the work of botanists and phytosociologists who listed, mapped and described
in detail the sites of different species of vegetation and their habitats
of high patrimonial value. The map below shows the Roscanvel peninsula in
Finistère, France, on a scale of 1:25.
More information
The website of the French National Botanical Conservatory in Brest www.cbnbrest.fr/botalittoral/
(French only).
All these effects are temporary. After the imbalance caused by the pollution, then the proliferation of resistant, recolonising organisms, the former balance is gradually restored, except if new pollution arrives. However, this return to normal can take years.
Did you know?
Reference condition
The contamination of the environment and the ecological impact of pollution
can only be fully appreciated when compared to reference values providing
an accurate representation of the situation before the accident. The creation
of reference conditions is the only way of demonstrating the causal relationship
between the spill of pollutant and the effects subsequently observed. This
implies that the information provided by these reference conditions must
be coherent with the particular needs of the ecological follow-up, in order
to provide an objective impact report.
To fulfil this need, and due to a growing demand for information on the
state and evolution of benthic flora and fauna, Ifremer (the French Research
Institute for Exploitation of the Sea), for example, launched and coordinated
in 2001 and 2002 a strategy for setting up a new surveillance and reference
data network for coastal benthic populations, known as the Rebent network.
This network has been up and running since 2003.
For more information, see www.rebent.org.
Follow-up of botanical restoration