INTRODUCTION TO THE MARINE ENVIRONMENT AND POLLUTION - Marine Pollution: What Everyone Needs to Know - page 14

allow for replication, so dose-response relationships under
controlled conditions can be studied. These kinds of studies
can show the differential sensitivity of different species and
can be used to learn about biological interactions. There is
much to be learned from such approaches. However, dosing
of complex mesocosms with known concentrations of specific
chemicals still does not really duplicate the natural environ-
ment in which organisms are subjected to many different pol-
lutants at different concentrations (which vary over time), and
where some of the species may have evolved increased resis-
tance to some contaminants. Thus, there remains uncertainty
with ecological risk assessments and with translating meso-
cosm results to real-world field situations.
It is usually very difficult to attribute problems seen in
the field to particular contaminants, because generally there
are many different contaminants at a site. In some rare cases,
observations on natural populations in the field called atten-
tion to effects of certain chemicals. This was the case with tri-
butyltin's (TBT) effects on oysters in Europe (see Chapter 8).
Since the abnormalities produced by TBT are unique and not
produced by other chemicals, the causal connection between
observed effects (abnormal shells in oysters) and the particu-
lar chemical (TBT) could be seen more easily.
Why are some species more sensitive to pollution than others?
Differences in sensitivity are due to differences in physiol-
ogy, generation time, and life cycle among species, which can
all affect initial responses and the ability to recover from the
effects. Species that are short-lived and produce large numbers
of offspring can exploit changing environments, including
contaminated ones. Such species with short generation times
also are more likely to be able to evolve tolerance to contami-
nants. High metabolic rates can lead to more rapid breakdown
of pollutants. In contrast, species that are long-lived, slow to
mature, and have relatively few offspring are less likely to be