Long Term Stability of Marine Ecosystems
John F. Dower
Department of Earth & Ocean Sciences
University of British Columbia
Abstract: Throughout most of history, the scientific community and the public at large
have tended to view marine ecosystems as static. Of course, this is not to say that
significant changes were never observed in the oceans, merely that it was generally
believed that, over long time-scales, thing stayed more or less the same. We assumed
that from year to year, decade to decade, the amount and distribution of fish in the
oceans should look roughly the same. This may stem from the fact that, historically, we
have usually only been interested in a single species in a given ecosystem. As long as
these species remained commercially abundant we assumed that everything was OK.
In fact, this belief in the stability of marine ecosystems is still popular today, as
evidenced by the use of fishing moratoria as the primary tool to deal with overfishing.
The underlying belief is that by stopping fishing, the ecosystem will necessarily go back
to “normal”.
In fact, marine ecosystems are not static. They can and do change, sometimes in very
dramatic ways, and sometimes over surprisingly short time scales. Understandably,
and particularly given our preoccupation with commercial species, such changes are
usually not noticed until they affect either the composition or the productivity of fish
communities. What causes these changes?
We now know that ecosystem change is both natural and, for the most part,
unavoidable. Much of what we are now learning about ecosystem change is coming
from advances in the use of paleo-techniques that ebable us to look at the structure of
marine ecosystems from 1000's of years ago. One particularly interesting finding is the
fact that many of the species that are commercially valuable to us today underwent
large natural cycles of productivity long before any significant fishing pressure was ever
exerted. In addition to natural factors such as climate change, however, we must also
face the grim fact that, in recent years, the most dramatic changes in marine ecosystem
structure have been brought about by human activities; primarily those of overfishing
and pollution.
Will it be possible to predict ecosystem changes in the future? Possibly. However, at
this point in time we still have a long way to go to even understand how and why
marine ecosystems change.