Environmental Engineering Reference
In-Depth Information
ecosystems. Thus, for example, in the sea, short-term variability is damped
out by very large heat capacity of the ocean. In turn, this large thermal
capacity and the long period exchange rates between deep and near-surface
waters leads to relatively large-amplitude changes at the long term scales
(Steele 1985). As a result, less robust internal ecosystem processes are
needed to handle the smaller amplitude variability at short periods. The
possible absence of such mechanisms, combined with increase variance
with period, can mean that pelagic marine populations or ecosystems have
to continually adapt to physical variability in the short as well as the long
term (Holling et al. 1995).
The absence of well structured recycling routes, the low recycling and
reduced stability of upwelling ecosystems can be considered a result of a
longer-term adaptation of biological community to the physical variability
and transitory nature of these systems. Bakun (1996) considered variability
itself as a key asset for the massive small pelagic wasp-waist populations
inhabiting upwelling systems, which must rely on pulsing its abundance
to cope with the temporal and spatial patterns presented by their prey,
while simultaneously presenting patterns to their predators that overcome
growth of intolerable levels of predation.
For instance, while the internalization of system activity by recycling
renders resistance to change (increasing stability), the lack of redundancy in
the recycling pathways could make it very diffi cult for a highly organized
system to reestablish broken pathways (Ulanowicz and Wulff 1991). In
this sense, the environmental price for stability would be a decrease in the
resilience of the studied ecosystem (Holling 1973), that is of their ability to
absorb changes and still persist in a state of high biomass.
The vulnerability of marine ecosystems, the value of the ecosystem
services they provide, and the need for different approaches in
understanding and managing human activities that affect oceans have
recently received much attention (Levin and Lubchenco 2008). Reports
from the Pew Oceans Commission (2003), the US Commission on Ocean
Policy (2004), the Joint Ocean Commission Initiative (2006), the Millennium
Ecosystem Assessment (2006), among others, draw attention to the seriously
disrupted state of marine ecosystems, a result of climate change, coastal
development, overexploitation of ocean resources, nutrient and chemical
pollution from the land, and other anthropogenic infl uences. Disruption of
marine ecosystems diminishes ecosystem services such as the provision of
fi sh and other seafood, the maintenance of water quality, and the control
of pests and pathogens (Levin and Chan 2012). The collective conclusion
of these reports is that if people wish to have safe seafood, stable fi sheries,
abundant wildlife, clean beaches, and vibrant coastal communities, priority
must be given to protecting and restoring the coupled land-ocean systems
that provide these services (Levin and Lubchenco 2008).
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