support more informed management to respond in more
effective ways. This awareness starts with a better knowledge and appreciation of the types of changes observed on
mangrove coasts and what can be inferred from key indicators of change.
Mangrove coasts as indicators of change
Tidal wetlands of the mangrove coast are ancient ecosystems having evolved over 100 million years. During this
time, the earth, sea-level, and climate have changed dramatically. Mangrove coasts of today are comprised of
plants that are the survivors of all previous changes
through the millennia. These ecosystems consequently
have well-developed strategies for survival with a defined
capacity for dealing with change. As tidal wetland ecosystems respond to change, they rely on inherent adaptive
capacity (Duke et al., 1998). Where changes can be identified, described, measured, and monitored, they form
the basis for a more enlightened monitoring and assessment strategy. For example, if a tidal wetland habitat had
shifted upland, this might demonstrate and quantify the
effects of sea-level rise. Two deductions to be made from
such observations are that mangroves responded to sealevel rise and that we might evaluate the rate of net change.
The value in this approach in combination with direct
instrument measures, like sea/tide level elevation stations,
is that mangrove coast plants integrate daily and seasonal
term fluctuations. These changes, when viewed from
above, are significantly enhanced along characteristically
low-profile slopes in numerous locations. Furthermore,
the exaggerated shifts can be readily determined retrospectively based on interpretation of vegetative condition
and specific location from historical aerial imagery.
There are also questions about what causes such
changes. This would be better understood if we were able
to expand our general knowledge and monitoring of the
full complement of forces or drivers that influence mangrove coasts. Such drivers act at local and global levels,
with some delivered directly, others indirectly, and, of
course, some are natural. In all situations, tidal wetlands
are responding to changing influences in characteristic
ways that are useful as indicators of change. With systematic identification of the different types of change in tidal
wetlands, we are able to identify the responsible drivers
and quantify their importance and anticipated
consequences.
Key pressures on mangrove coasts
Pressures on mangrove coasts with their tidal wetlands
(Figure 2) can be conveniently grouped under three broad
headings (Duke et al., 2003):
• Direct human pressures, as mostly intended and
obvious
• Indirect human pressures, as mostly unintended and less
obvious
• Natural; being not obviously human influenced, if at all
These classifications are useful when making decisions
about sustainable management of coastal and estuarine
ecosystems, and they form the basis for classification of
all types of observed change. As it happens, the more
direct human influences are those that are more easily mitigated, resulting in relatively rapid, improved environmental outcomes. By contrast, it has been inherently
difficult to differentiate between human and natural influences on global temperatures. So, it is appropriate at this
time to group these more indirect human influences along
with the natural pressures. This accepts that some drivers
might be somewhat subjective with overlaps and
ambiguity.
Indicators of change in mangrove coasts
Changes are usually measured in terms of ecosystem
responses to external pressures. Estuarine, coastal, and
marine ecosystems are influenced by a number of key factors acting as primary stressors and drivers. The responses
of affected habitats are often unique and distinctive making them useful indicators of the key drivers.
The six overall drivers of change for mangrove coasts
may be grouped under the following headings:
• Severe Human Disturbance
• Hydrology and Sediments
• Pollutants
• Pests and Pathogens
• Climate Change
• Severe Natural Disturbance
While these drivers often act in combination, their
effects on tidal wetland ecosystems however predominantly result in recognizable and distinct responses. These
outcomes are often observed in patches of habitat dominated by dramatic and noticeable change. In such
instances, the key characteristics and features present can
be used as an indicator, or proxy, of each dominant
prevailing driver. Based on such information, it is possible
to develop more effective management intervention
actions taking account of the full array of circumstances.
For instance, where pressures are largely natural or globally affected, then a local management response might
best be one of adaptation and accommodation. By contrast, if a stressor were predominantly locally derived, then
this could be managed and controlled locally to mitigate
such effects. The difference between these two management response options is extreme. It emphasizes why prior
knowledge of influencing factors and change can greatly
facilitate effective and sustainable outcomes.
In general, the many specific types of change can be
grouped under each of these headings (Figure 2).
Twenty-one types of change are listed. These represent
most of all possible changes likely. The following sections
describe briefly the drivers of change and the influencing
factors affecting mangrove coasts; along with some illustrative examples. Comparative quantification of these
pressures essentially can be derived from measures of area
MANGROVE COASTS
415
effective ways. This awareness starts with a better knowledge and appreciation of the types of changes observed on
mangrove coasts and what can be inferred from key indicators of change.
Mangrove coasts as indicators of change
Tidal wetlands of the mangrove coast are ancient ecosystems having evolved over 100 million years. During this
time, the earth, sea-level, and climate have changed dramatically. Mangrove coasts of today are comprised of
plants that are the survivors of all previous changes
through the millennia. These ecosystems consequently
have well-developed strategies for survival with a defined
capacity for dealing with change. As tidal wetland ecosystems respond to change, they rely on inherent adaptive
capacity (Duke et al., 1998). Where changes can be identified, described, measured, and monitored, they form
the basis for a more enlightened monitoring and assessment strategy. For example, if a tidal wetland habitat had
shifted upland, this might demonstrate and quantify the
effects of sea-level rise. Two deductions to be made from
such observations are that mangroves responded to sealevel rise and that we might evaluate the rate of net change.
The value in this approach in combination with direct
instrument measures, like sea/tide level elevation stations,
is that mangrove coast plants integrate daily and seasonal
term fluctuations. These changes, when viewed from
above, are significantly enhanced along characteristically
low-profile slopes in numerous locations. Furthermore,
the exaggerated shifts can be readily determined retrospectively based on interpretation of vegetative condition
and specific location from historical aerial imagery.
There are also questions about what causes such
changes. This would be better understood if we were able
to expand our general knowledge and monitoring of the
full complement of forces or drivers that influence mangrove coasts. Such drivers act at local and global levels,
with some delivered directly, others indirectly, and, of
course, some are natural. In all situations, tidal wetlands
are responding to changing influences in characteristic
ways that are useful as indicators of change. With systematic identification of the different types of change in tidal
wetlands, we are able to identify the responsible drivers
and quantify their importance and anticipated
consequences.
Key pressures on mangrove coasts
Pressures on mangrove coasts with their tidal wetlands
(Figure 2) can be conveniently grouped under three broad
headings (Duke et al., 2003):
• Direct human pressures, as mostly intended and
obvious
• Indirect human pressures, as mostly unintended and less
obvious
• Natural; being not obviously human influenced, if at all
These classifications are useful when making decisions
about sustainable management of coastal and estuarine
ecosystems, and they form the basis for classification of
all types of observed change. As it happens, the more
direct human influences are those that are more easily mitigated, resulting in relatively rapid, improved environmental outcomes. By contrast, it has been inherently
difficult to differentiate between human and natural influences on global temperatures. So, it is appropriate at this
time to group these more indirect human influences along
with the natural pressures. This accepts that some drivers
might be somewhat subjective with overlaps and
ambiguity.
Indicators of change in mangrove coasts
Changes are usually measured in terms of ecosystem
responses to external pressures. Estuarine, coastal, and
marine ecosystems are influenced by a number of key factors acting as primary stressors and drivers. The responses
of affected habitats are often unique and distinctive making them useful indicators of the key drivers.
The six overall drivers of change for mangrove coasts
may be grouped under the following headings:
• Severe Human Disturbance
• Hydrology and Sediments
• Pollutants
• Pests and Pathogens
• Climate Change
• Severe Natural Disturbance
While these drivers often act in combination, their
effects on tidal wetland ecosystems however predominantly result in recognizable and distinct responses. These
outcomes are often observed in patches of habitat dominated by dramatic and noticeable change. In such
instances, the key characteristics and features present can
be used as an indicator, or proxy, of each dominant
prevailing driver. Based on such information, it is possible
to develop more effective management intervention
actions taking account of the full array of circumstances.
For instance, where pressures are largely natural or globally affected, then a local management response might
best be one of adaptation and accommodation. By contrast, if a stressor were predominantly locally derived, then
this could be managed and controlled locally to mitigate
such effects. The difference between these two management response options is extreme. It emphasizes why prior
knowledge of influencing factors and change can greatly
facilitate effective and sustainable outcomes.
In general, the many specific types of change can be
grouped under each of these headings (Figure 2).
Twenty-one types of change are listed. These represent
most of all possible changes likely. The following sections
describe briefly the drivers of change and the influencing
factors affecting mangrove coasts; along with some illustrative examples. Comparative quantification of these
pressures essentially can be derived from measures of area
MANGROVE COASTS
415