Marine Ecosystems under Toxic Pressure - Vulnerability of Coastal Ecosystems and Adaptation - page 20

1.4.1.1. Predator-prey interactions (top-down)
The “top-down” effects are triggered when a predator is more
sensitive to a contaminant than its prey (Figure 1.3). This sensitivity,
without consequently directly causing the predator's death, can
modify the ingestion and/or predation rates [GRE 97, WAL 00,
WEI 01, WID 91] and thus causes an increase in the abundance of the
prey (Figure 1.6). “Top-down” effects have thus been used as
evidence in marine benthic systems after contamination by metals,
fungicides and hydrocarbons [BEL 00, CAR 97, LAY 85, JAK 96,
VAN 00]. These different contaminations have all led to trophic
cascades. In addition to reducing pressure from predation, the
contaminants can also benefit producers via the release of nutrients
from the decomposition of deceased animals [KNA 05].
Figure 1.6. Illustration of indirect “top-down” effects
of contaminants (modified from [FLE 03])
C OMMENTARY ON F IGURE 1.6 .- Box 1 represents a community of
primary producers and two species of grazers (A = dominant; B = rare)
before modification by a contaminant. Box 2 shows the result of a
possible direct effect (rapid and selective) of the contaminant on the