Marine Ecosystems under Toxic Pressure - Vulnerability of Coastal Ecosystems and Adaptation - page 3

trophic oceanic chain, which feeds not only the sea birds... but also
people.
First, these are the details of the ocean environment that are
affected vis-à-vis the toxic pressure. Then, the biological responses
will be described at the level of individuals exposed to toxic pressure,
independent of each another (“direct effects”). Finally, the focus turns
to the group of effects known as “indirect effects”, that is to say, those
that affect the relationships between the individuals of which an
ecosystem is composed. Little is yet known about these indirect
effects, but initial observations have tended to show that they are the
primary impact; understanding the behavior of these systems under
toxic pressure has to be taken into account.
1.2. Details of the marine environment
All aquatic environments are subject to pollution of anthropogenic
origin, and all the associated ecosystems are subject to the toxic stress
that results. The ocean, because of its dimensions - it is the most vast
of the biosphere's ecosystems (1.4 billion km 3 ) whose depth reaches,
on average 3,800 m - and because of its distance from the continents
appears relatively protected in comparison to rivers and lakes. Rivers
and lakes are often very directly impacted by human use: runoff from
agricultural land or soil that has been made impermeable, sources of
diverse phytosanitary products, hydrocarbons, dioxins, metals, etc.;
they are the recipients of more or less well-treated collection
networks, sources of molecules from pharmaceutical synthesis,
cosmetics, detergents, products from eroded materials, etc.; outlets,
finally, of the widespread contamination of our environment by
extremely varied products (see also Chapters 2 and 3). Locally, the
impacts of these contaminations can be very pronounced (for example
[DED 09], chemosphere), even if they are difficult to prove, because
of the mobility of flowing water [FEC 14] and the physico-chemical
variability of these environments: diurnal variations in pH and
temperature, seasonal variations in organic matter and in shade from
forest cover, regional variations in the concentration of eroded
minerals, etc., all are modulating factors in the bioavailability of the
contaminants [TUS 07].