METALS - Marine Pollution: What Everyone Needs to Know - page 92

it is not bioavailable. However, under low pH (acidic) condi-
tions in freshwater that can result from acid rain, it becomes
available. If a freshwater stream is affected by acid rain, young
salmon get exposed to Al as well as to acidity, both of which
cause toxic effects. Short-term Al-exposure and moderate
acidification increase mortality in fish migrating downstream,
and can reduce Atlantic salmon populations, according to
Frode Kroglund and Bengt Finnstad. Al reduces their ability
to adjust to salinity changes, so these young fish die when they
approach seawater. Al also decreases growth hormone levels,
and can cause stress and death.
Behavior is a particularly sensitive response to contami-
nants. Noticeable changes in behavior can be found at low con-
centrations of chemicals such as methylmercury (meHg), lead
(Pb), or copper (Cu). In addition to being sensitive, behavioral
changes can produce ecological effects at the population and
community level, as shown by Weis and colleagues. Behaviors
that have been studied include swimming, burrowing, migra-
tion, prey capture, predator avoidance, reproductive behav-
iors, aggression, and social interactions. Effects on behavior
may be direct or indirect. Indirect effects include alteration of
activity or reproductive success due to reduced feeding, and
thus less energy. Behavior can be seen in larval or older stages
after earlier exposure to pollutants during embryonic stages.
It is also possible to trace behavioral alterations back to
underlying neurological effects of the contaminants. For exam-
ple, Cu is especially toxic to the olfactory system of fish, which
means that species that rely on their sense of smell for naviga-
tion or detecting the presence of predators (or prey) cannot do
so as well. If salmon streams are contaminated with Cu, the
very sensitive early stages of these migratory fish are dam-
aged and their navigation during subsequent migration can
be impaired, according to James Hansen and colleagues. Cu is
also especially toxic to snails, which retreat into their shells and
remain inactive while it is present. Oysters, on the other hand,
can accumulate high concentrations of copper, so much that in