110
A.J. Underwood . M.G. Chapman
cult to interpret. If data from a long enough time-course before and after a marina is
built are not available, comparisons can still be made between ongoing facilities and
control locations (Glasby 1997b). Careful consideration needs to be given to the location of appropriate controls (Green 1979) and spatial and temporal scales of sampling
(Underwood 1992, 1994a). Future management of such facilities will also be improved
if each marina is not treated on a case-by-case basis. In busy estuaries, environmental
decisions about the development and functioning of marinas are being made continuously. Each of these decisions is an experiment, with a predicted outcome. If these decisions and tests of their predicted outcomes can be amalgamated, managers could
develop more powerful (and general) methods of assessing effects of facilities such as
marinas. This requires, however, a very different approach on the part of planners and
managers to the way in which environmental impact is assessed.
,Note that, as is the case with many ongoing activities, such as recreational boating,
it is often assumed that any impacts are due to current activities. This needs more careful consideration by managers. For example, if developments, such as marinas, are carefully built in particular parts of estuaries (perhaps because of shelter from waves or
wind), then these areas may contain different assemblages of animals and plants, prior
to any development. It will then be very difficult to distinguish between prior differences in the assemblages and ongoing differences cased by the activities of the marina
itself, unless data are obtained prior to the development.
Finally, there is an increasing tendency to change from pylons and fixed jetties to
walkways with free-floating pontoons for attachment of the boats. This. is, in part, due
to decreased costs of maintenance and in part due to the perception that free-floating
structures will allow greater flow of water and therefore be more "environmentally
friendly". The surfaces of floating structures may support dense assemblages of animals (Fletcher 1980), many of which may not generally be found in nearby natural structures. Similar structures, such as racks for cultivation of mussels, have very deleterious effects on the sediments below the racks, because of the large quantities of waste
produced (Kaspar et al. 1985). The consequences of the decision to change from jetties
to floating pontoons are not known and do not necessarily appear to be under consideration. The necessary experiments to test for the environmental effects of this decision are straightforward, but relatively expensive (testing environmental effects on
assemblages in sediments is generally expensive because of the time needed to sort
samples). They are, however, necessary. Mangers need to recognize the potential consequences of their decisions and to plan experimental tests of these consequences before decisions become widespread and generally accepted as "good for the environment".
6.3.3
Restoration of Wetlands
As another example, consider the managerial decision to restore (rehabilitate) wetlands
or other degraded and damaged habitats. The reasons for such a decision are usually
specific to each project and often driven by societal (rather than ecological) needs. For
example, damaged habitats may be restored to provide recreational or aesthetic amenities. Even when the stated need is restoration of habitat for wildlife (Zedler 1996), it is
not always dear that the process of restoration will achieve this. Restoration is frequently
A.J. Underwood . M.G. Chapman
cult to interpret. If data from a long enough time-course before and after a marina is
built are not available, comparisons can still be made between ongoing facilities and
control locations (Glasby 1997b). Careful consideration needs to be given to the location of appropriate controls (Green 1979) and spatial and temporal scales of sampling
(Underwood 1992, 1994a). Future management of such facilities will also be improved
if each marina is not treated on a case-by-case basis. In busy estuaries, environmental
decisions about the development and functioning of marinas are being made continuously. Each of these decisions is an experiment, with a predicted outcome. If these decisions and tests of their predicted outcomes can be amalgamated, managers could
develop more powerful (and general) methods of assessing effects of facilities such as
marinas. This requires, however, a very different approach on the part of planners and
managers to the way in which environmental impact is assessed.
,Note that, as is the case with many ongoing activities, such as recreational boating,
it is often assumed that any impacts are due to current activities. This needs more careful consideration by managers. For example, if developments, such as marinas, are carefully built in particular parts of estuaries (perhaps because of shelter from waves or
wind), then these areas may contain different assemblages of animals and plants, prior
to any development. It will then be very difficult to distinguish between prior differences in the assemblages and ongoing differences cased by the activities of the marina
itself, unless data are obtained prior to the development.
Finally, there is an increasing tendency to change from pylons and fixed jetties to
walkways with free-floating pontoons for attachment of the boats. This. is, in part, due
to decreased costs of maintenance and in part due to the perception that free-floating
structures will allow greater flow of water and therefore be more "environmentally
friendly". The surfaces of floating structures may support dense assemblages of animals (Fletcher 1980), many of which may not generally be found in nearby natural structures. Similar structures, such as racks for cultivation of mussels, have very deleterious effects on the sediments below the racks, because of the large quantities of waste
produced (Kaspar et al. 1985). The consequences of the decision to change from jetties
to floating pontoons are not known and do not necessarily appear to be under consideration. The necessary experiments to test for the environmental effects of this decision are straightforward, but relatively expensive (testing environmental effects on
assemblages in sediments is generally expensive because of the time needed to sort
samples). They are, however, necessary. Mangers need to recognize the potential consequences of their decisions and to plan experimental tests of these consequences before decisions become widespread and generally accepted as "good for the environment".
6.3.3
Restoration of Wetlands
As another example, consider the managerial decision to restore (rehabilitate) wetlands
or other degraded and damaged habitats. The reasons for such a decision are usually
specific to each project and often driven by societal (rather than ecological) needs. For
example, damaged habitats may be restored to provide recreational or aesthetic amenities. Even when the stated need is restoration of habitat for wildlife (Zedler 1996), it is
not always dear that the process of restoration will achieve this. Restoration is frequently