An approach to sensitivity assessment
The following information regarding sensitivity
assessment provides just one example of how such a review can
be undertaken. It is not an example of the specific techniques
and procedures followed by the Countryside Agencies, and in
no way reflects the views and opinions of the agencies.
Assessing Feature Sensitivity
Sensitivity analysis has been carried out on
coastal sites mainly to assess the possible effects of oil spills.
More recently, a number of projects have been assessing the
sensitivity of marine areas to recreational use.
‘Sensitivity’ was defined by Hiscock (1996)
as ‘the intolerance of a habitat, community or individual of
a species to damage or death from an external factor".
It is important to distinguish between intolerance, (intolerance
- the inability of a habitat, community or individual
(or individual colony) or a species to cope with exposure to
an external factor) which brings about death or reduces populations
to levels from which recovery is impossible or very unlikely,
and intolerance to damage from which recovery and survival may
be possible with repair of the damage. Assessment of sensitivity
therefore needs to take account of ‘recoverability’ –
the ability of a species to return to its former status once
original conditions return (MacDonald et al 1996). However,
the Habitat Directive Regulations do not include characteristics
of the activity within the guidance on assessment criteria and
in addition some of these factors may not be relevant to the
sensitivity of the site features.
Changes in behaviour, displacement from breeding
or feeding grounds or long and short term disturbance may be
important indicators of responses to stressors, but they may
also occur as part of the natural long-term life cycle of specific
For marine recreational activities, it may
be possible to assess feature vulnerability, (vulnerability
- the exposure of a habitat, community or individual
(or individual colony) to an external factor to which it is
sensitive (Hiscock, 1996), both geographically (spatially) and
also across time periods (temporal). Some organisms may not
be vulnerable/sensitive to a particular action if they are frequently
exposed to a particular stress. However, the same species in
another location, which does not commonly experience this stress,
may be sensitive/vulnerable because natural resistance to the
stress or acceptance of the activity has not evolved. However,
there is insufficient knowledge about the recoverability of
many marine habitats and species that may be vulnerable to marine
Assessment of sensitivity to recreational use
has typically focused on ‘spatial’ vulnerability – the existence
of a species or habitat in a given location that is likely to
be affected by a specified activity. This must take account
of the time scale over which changes occur. For example, a recreational
activity that has the potential to cause damage may only occur
when the species at risk is absent. As recreational activities
are now carried out throughout the year, impacts may increase
particularly on species that locate in the area on a seasonal
basis. For example, improved wetsuit technology has extended
the season for immersion sports into the winter season. Often
such activities will access the water via intertidal sand and
mudflats. At high tide potential effects will be limited, but
at low tide these mud flat areas are used by wintering waterfowl
for food and rest. Disturbance may occur to species that only
use the site during the winter period.
The potential for an increase in the conflict
between nature conservation interests and recreational interests
thus becomes greater as new and seasonally unrestricted recreational
activities introduce new stresses into the marine environment.
Conflicts between innovative new uses and established ones may
bring about changes in the location of activities and so spread
the stresses on marine species and habitats to new areas. However,
there is only limited understanding of these effects as species
and communities can be highly sensitive to some stresses and
not at all sensitive to others.
Sensitivity assessment is a flexible approach
that can be applied at any geographical or temporal scale. It
is consistent with both sustainable management and the development
of sustainability indicators. The key feature of sensitivity
assessment is that it takes a holistic approach to the impacts
of activities on the environment, identifying those areas most
susceptible to change (whether positive or negative). It considers
the tolerances and thresholds of features to different types
and scale of activity and is flexible to emerging trends.
Sensitivity assessment should be an integral
part of any project planning process and is not scale limited.
It has demonstrable benefits in that it provides the baseline
upon which more detailed studies and assessments can be carried
out (perhaps at EIA level if necessary).
Some approaches to sensitivity assessment use
a flow diagram template against which case studies can be tested.
This provides a pathway through the process of decision making,
making it easily understood. It relies on a simple set of questions
asked at key points. The response provides a particular pathway
to the next step of the process.
Sensitivity assessment can also help to identify
the most critical assets within an area to be protected whilst
allowing sustainable management for the optimal (but not maximum)
use of marine resources. The more comprehensive and reliable
the information which feeds into the assessment process, the
smaller the critical areas identified are likely to be. The
critical areas are of course the core areas for management and
will be based upon sensitivity of the features and existing
and potential activities within the area as well as external
The Process of Sensitivity Assessment
It is generally agreed that the following questions
need to be asked in order to identify the levels of sensitivity
of a feature and the vulnerability induced by recreational activities.
What are the Characteristics of the Feature?
The size, abundance, rarity, robustness, distribution,
and social importance of the feature need to be reviewed. The
level and format of the information which is currently available
will dictate the effective completion of this step in the process.
relevant authorities, site managers and recreational participants
should be aware of issues concerned with quality assurance of
the information base and questions need to be asked about the
the source of information
reliability of data and information
completeness of data/information
levels of understanding of this information
Once these questions have been considered,
if lack of information restricts the decision making process
further, information requirements should be highlighted and
appropriate research undertaken. It is especially important
to identify both Characteristic Species ( special or
especially abundant in a particular situation or biotape. Characteristic
species should be immediately conspicuous and easily identified
(based on Hiscock & Connor, 1991 in Hiscock, 1996) and Keystone
Species (biologically structuring species that are vital
to the ecological integrity of communities, and whose absence
would cause the community to significantly alter, dysfunction
or disappear (Masters & Gee, 1995).
To What is the Feature Sensitive?
Relevant authorities, site managers and others
involved in the policy process should be aware of the possible
implications of natural processes and human uses of the site
and their effects on its sensitivity. Furthermore they should
take steps to assess the vulnerability of the site and its species.
This will be dependent upon the available data and information.
Consideration should be given to the quality of the information
and if necessary further research should be commissioned to
aid the development of policy and practices.
What are the Characteristics of the Activity?
For each mSAC site, consideration should be
given to a range of both natural and human criteria. These include
the area’s size and extent, naturalness and fragility. Specific
recreational issues include diversity and levels of activities,
aesthetic appeal, cultural significance, etc.
What are the Levels of Acceptable Change (LACs)?
The levels of stress imposed on a site, feature
or community will have implications for its overall stability.
High species richness is maintained in communities at intermediate
scales of disturbance. However, additional levels of stress
may cause damage or disruption to the feature or community.
It is essential to establish the limits of recoverability with
respect to specified disturbances for natural and managed communities.
The extent to which a community may be disturbed before it shifts
to a less desirable form should also be assessed. The sensitivity
assessment should provide a basis for judging the probability
and acceptability of these threats. The checklist boxes below
summarise the main issues to be considered:
What features are located in the site (both
habitats and species)?
Is the value of the habitat geological,
archaeological or geomorphological or as a home for keystone
How resilient are the habitat’s geological,
archaeological and geomorphological features?
Are keystone species valuable at a community
level or at an individual species level?
To what extent do external stresses, including
those caused by recreational activities, affect the habitat,
species or community?
Is the habitat/species able to cope with
stresses (is it robust?)
Is the habitat/species able to recolonise
following exposure to an external factor?
Is the species able to avoid the effects
of such exposure by temporary emigration or withdrawal into
shell or shelter?
Is this ability to avoid the effects driven
by other factors, eg proximity of other populations, barriers
Figure 2 Recreational Issues to Consider
Are human influences direct – physical
damage, disturbance, degradation?
Are the levels of these impacts occasional,
regular or constant?
Are human influences indirect, eg competition
for space, water, quality, noise?
Are the levels of these effects occasional,
regular or constant?
Where do these impacts take place?
Are the locations static or do pressure
points change depending on the season?
Are they land side or water side effects?
The above process should provide the following
Assessment of sensitivity of a habitat or species,
at the level of the species' ability to cope/recolonise/avoid.
Identification of the source of disturbance
and assessment of its effects on the habitat and species’ sensitivity.
For example, if the stress is repeated but the organism has
strategies for temporary avoidance, the species suffers damage
but is able to cope.
Once this process has been completed, it may
be possible to devise a scale of sensitivity to summarise the
findings. Having identified the component impact associated
with a maritime activity (a sensitivity factor), it may be possible
to assess the factor intensity, i.e. the magnitude of a factor
on a pre-defined scale.
In practice, for many species it will not be
possible to assign their sensitivity to more than a simple scale
of neutral, sensitive, neutrally sensitive or damaged, and so
for many sites the simple allocation of species, sites, features
and communities to a sensitivity scale of benign, neutral
or damaged will be the initial level at which sensitivity
can be assessed. There will be overlapping sensitivities, thus
in a specific area one species may be very sensitive to particular
recreational activities whereas others are unaffected. Judgements
need to be made about the geographical resolution to which sensitivities
will be applied. Nevertheless, it is essential to recognise
that habitats, processes and organisms are often finely tuned
to disturbance, but that once a sensitivity threshold has been
crossed, recovery may be slow or impossible.
It should be possible to use the following
or similar statements to judge the level of sensitivity:
The action positively effects the process or
eg marina construction provides a new rocky
habitat for limpets.
The habitat, processes or organisms are sensitive
to short term disturbance, eg birds fly from feeding areas when
disturbed by a passing vessel, then settle back to the earlier
If a disturbance is repeated or sufficiently
intense, organisms move to alternative areas, although they
may re-occupy the area if the source of disturbance is removed,
eg a change of wind direction requires change in launch points
or accidental spillage of fuel causes localised bird mortalities.
This level of disturbance may also affect organisms’ breeding
The habitat, process or organism is sufficiently
sensitive that if further stresses from other activities occur
it will be seriously damaged and become fatally sensitive. For
example, a small breeding population already adversely affected
by climate is disturbed by increase in water-based recreation
during breeding season (this is probably sub-lethal).
The habitat, process or organism is so sensitive
to this effect that it will die or change irrevocably.
To assess the possible negative or positive
implications of recreation on specific marine features or species,
it is important to have an understanding and appreciation of
the often variable and complex nature of these features.
It is important that observed changes are not
automatically attributed to human disturbance.
To place observed changes within the context
of natural variations over time and the variety of human uses
of the coast it is important to make an assessment of the sensitivity,
recoverability and vulnerability of designated site features.
It is also important to distinguish between
‘intolerance’ to an action from which recovery is impossible
and 'intolerance' to an action from which recovery and survival
may be possible.
Sensitivity assessment provides a robust, flexible
and holistic approach.
The Marlin project supported by the Marine Biological Association
is developing a biological sensitivity database. Its website