Marine Ecosystems under Toxic Pressure - Vulnerability of Coastal Ecosystems and Adaptation - page 18

Figure 1.5. Direct and indirect effects of environmental stress
on biological systems (taken from [ADA 05a])
The direct effects affect organisms by acting on the biochemical
and metabolic processes; indirect effects disrupt the biota 2 via the
availability of food and habitat, and via intra- and inter-species
interactions.
1.4. Consequences of toxic pressure on ecosystems
When pollutants are ejected into aquatic ecosystems, direct (toxic)
effects on biota are possible. These direct effects of toxic substances
tend to reduce the number of organisms (by an increase in mortality
and/or a decrease in fertility). The biota of a given habitat often show
a large range of tolerance to specific toxic substances (for example,
insecticides and herbicides target specific organisms in a community),
the toxin can have lethal effects on certain species, but have no
observable effect on others. Pollutants can, however, have effects on
tolerant species through a number of ecological mechanisms. These
2 A group of living organisms present in a particular habitat or more generally in a
given region.