Biodiversity & Conservation

Sensitivity assessment rationale - a summary


The sensitivity assessment rationale was developed by the MarLIN team in consultation with the MarLIN Technical Management Group and ratified by the MarLIN programme Steering Group, both of which include representatives of the major users of marine information, statutory agencies, regulators, and marine research institutes. The MarLIN sensitivity assessment rationale, definitions of terms and scales used prior to March 2003 are given by Tyler-Walters et al. (2001) and their development in Tyler-Walters & Jackson (1999) and Hiscock et al. (1999) (Go to reports). The definition of sensitivity was revised in March 2003 based on the definition suggested by the RMNC (Laffoley et al., 2000) and developed by MarLIN in consultation with our Technical Management Group and Sensitivity Mapping Advisory Group.

The revised 'sensitivity' scale introduced another step into the MarLIN approach to sensitivity assessment previously outlined in Tyler-Walters et al. (2001) and on the MarLIN Website. The revised sensitivity assessment rationale for species and biotopes, as amended in March 2003, is summarized below together with the relevant definitions of intolerance, recoverability, and sensitivity.

The MarLIN approach to assessing sensitivity built on a review of the strengths and weaknesses of existing and prior approaches to sensitivity assessment, especially earlier work by Holt et al. (1995, 1996), which thought through many of the concepts of vulnerability, sensitivity, and recoverability. Studies commissioned or undertaken by the nature conservation agencies in the UK, the ICES Benthos Working Group workshops and meetings of the OSPAR IMPACT group, the recent Review of Marine Nature Conservation (RMNC) (Laffoley et al., 2000), together with subsequent development by MarLIN, have all contributed to the core definitions below.

Core definitions


'Biotope' refers to the combination of physical environment (habitat) and its distinctive assemblage of conspicuous species. For practical reasons of interpretation of terms used in directives, statutes and conventions, in some documents, 'biotope' is sometimes synonymized with 'habitat'.

'Habitat' the place in which a plant or animal lives. It is defined for the marine environment according to geographical location, physiographic features and the physical and chemical environment (including salinity, wave exposure, strength of tidal streams, geology, biological zone, substratum), 'features' (such as crevices, overhangs, or rockpools) and 'modifiers' (for example sand-scour, wave-surge, or substratum mobility).

'Community' refers to a group of organisms occurring in a particular environment, presumably interacting with each other and with the environment, and identifiable by means of ecological survey from other groups. The community is usually considered the biotic element of a biotope.

'Intolerance' is the susceptibility of a habitat, community or species (i.e. the components of a biotope) to damage, or death, from an external factor. Intolerance must be assessed relative to change in a specific factor.

'Recoverability' is the ability of a habitat, community, or species (i.e. the components of a biotope) to return to a state close to that which existed before the activity or event caused change.

'Sensitivity' is dependent on the intolerance of a species or habitat to damage from an external factor and the time taken for its subsequent recovery. For example, a very sensitive species or habitat is one that is very adversely affected by an external factor arising from human activities or natural events (killed/destroyed, 'high' intolerance) and is expected to recover over a very long period of time, i.e. >10 or up to 25 years ('low'; recoverability). Intolerance and hence sensitivity must be assessed relative to change in a specific factor.

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Assessing the sensitivity of species


The assessment rationale involves judging the intolerance of a species to change in an external factor arising from human activities or natural events. The rationale then assesses the likely recoverability of the species following cessation on the human activity or natural event. Intolerance and recoverability are then combined to provide a meaningful assessment of their overall sensitivity to environmental change.

The rationale used to prepare a review of the biology and sensitivity key information for a species is given below.

  1. Collate key information on the species. The best available scientific information required to describe the biology and likely sensitivity of the species is collated using the resources of the National Marine Biological Library (NMBL), the World Wide Web, and the expertise of marine biologists based at the Marine Biological Association of the UK (MBA), Plymouth.

  2. Indicate quality of available data. The MarLIN programme operates an internal quality assurance procedure, to ensure that only the most accurate available information is provided on-line. The quality of the available evidence and our confidence in our assessments (based on availability of information) is clearly stated and ranked against a standard scale (see evidence/confidence scale).

  3. Assess the intolerance of the species to change in environmental factors. The likely intolerance of the species is assessed with respect to a specified magnitude and duration of change (view benchmarks) for 24 separate environmental factors (see list of environmental factors).

    Precedence is given to direct evidence of effect or impact. For example, information from targeted studies / experiments that looked at the effect of the specific factor on the species, or targeted work / experiments on the effects of similar factors on similar species or studies of the likely effects of a factor. The assessment of intolerance (see intolerance scale) is then made by reference to the reported change in environmental factors and their impact, relative to the magnitude and duration of the standard benchmarks and other relevant key information.

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    In the absence of direct evidence, the MarLIN rationale includes simple decision trees to aid intolerance and recoverability assessment based on the available key information for the species. The decision trees provide a systematic and transparent approach to assessment. The decision trees are described in full by Tyler-Walters et al. (2001) (Go to Reports page).

  4. Assess the recoverability of the species. The likely recoverability of a species from disturbance or damage is dependent on its ability to regenerate, regrow, recruit or recolonize, depending on the extent of damage incurred and hence its intolerance. The recoverability of a species is assessed against the recoverability scale (see recoverability scale) by reference to direct evidence of recruitment, recolonization or recovery (e.g. after environmental impact or experimental manipulation in the field) and/or key information on the reproductive biology, habitat preferences and distribution of the species.

    Precedence is given to direct evidence of the effects of changes in environmental factors on a habitat, its community and associated species (i.e. the components of a biotope), and its subsequent recovery. The intolerance of a biotope to change in each environmental factor is assessed against a standard 'benchmark' level of effect (view benchmarks), which allows the user to compare the recorded sensitivity to the level of effect predicted to be caused by a proposed development or activity. The evidence and key information used to assess sensitivity and any judgements made are explained in the on-line rationale for each assessment. The source of all information used is clearly referenced on-line.

  5. Assess the sensitivity of the species. The overall sensitivity rank is derived from the combination of intolerance and recoverability using the rationale shown in Table1 and Table 2.

    The sensitivity assessment rationale uses the question 'does it matter if?', together with the definitions of sensitive habitats and species proposed in the Review of Marine Nature Conservation (Laffoley et al., 2000) as touch-stones throughout. Due to the importance of recoverability in assessing the continued survival of a habitat or species population, the scale is intuitively weighted towards recoverability. However, where recovery is likely to occur in a short period of time, intolerance has been given a greater weight rather than under-estimate the potential sensitivity of marine habitats and species. The sensitivity scales and definitions are designed to be meaningful in marine environmental management, protection, and conservation.

    For instance, if a habitat or species is very adversely affected by an external factor arising from human activities or natural events (killed/destroyed, 'high' intolerance) and is expected to recover over a very long period of time, i.e. >10 or up to 25 years ('low'; recoverability) then it would be considered to be highly sensitive. Similarly, if a habitat or species is adversely affected by an external factor arising from human activities or natural events (damaged, 'intermediate' intolerance) but is expected to recover in a short period of time, i.e. within 1 year or up to 5 years ('very high' or 'high' recoverability) then it would be considered to be of low sensitivity. The scenarios used to derive the sensitivity scale are listed in Table1.

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    Table 1

    Defining 'sensitivity' sensu lato for habitats and species. (**) 'Reduced viability' includes physiological stress, reduced fecundity, reduced growth, and partial death of a colonial animal or plant.

    Rank Definition
    Very High "Very high" sensitivity is indicated by the following scenario:
    • The habitat or species is very adversely affected by an external factor arising from human activities or natural events (either killed/destroyed, "high" intolerance) and is expected to recover only over a prolonged period of time, i.e. >25 years or not at all (recoverability is "very low" or "none").
    • The habitat or species is adversely affected by an external factor arising from human activities or natural events (damaged, "intermediate" intolerance) but is not expected to recover at all (recoverability is "none").
    High "High" sensitivity is indicated by the following scenarios:
    • The habitat or species is very adversely affected by an external factor arising from human activities or natural events (killed/destroyed, "high" intolerance) and is expected to recover over a very long period of time, i.e. >10 or up to 25 years ("low" recoverability).
    • The habitat or species is adversely affected by an external factor arising from human activities or natural events (damaged, "intermediate" intolerance) and is expected to recover over a very long period of time, i.e. >10 years (recoverability is "low", or "very low").
    • The habitat or species is affected by an external factor arising from human activities or natural events (reduced viability **, "low" intolerance) but is not expected to recover at all (recoverability is "none"), so that the habitat or species may be vulnerable to subsequent damage.
    Moderate "Moderate" sensitivity is indicated by the following scenarios:
    • The habitat or species is very adversely affected by an external factor arising from human activities or natural events (killed/destroyed, "high" intolerance) but is expected to take more than 1 year or up to 10 years to recover ("moderate" or "high" recoverability).
    • The habitat or species is adversely affected by an external factor arising from human activities or natural events (damaged, "intermediate" intolerance) and is expected to recover over a long period of time, i.e. >5 or up to 10 years ("moderate" recoverability).
    • The habitat or species is affected by an external factor arising from human activities or natural events (reduced viability **, "low" intolerance) but is expected to recover over a very long period of time, i.e. >10 years (recoverability is "low", "very low"), during which time the habitat or species may be vulnerable to subsequent damage.
    Low "Low" sensitivity is indicated by the following scenarios:
    • The habitat or species is very adversely affected by an external factor arising from human activities or natural events (killed/destroyed, "high" intolerance) but is expected to recover rapidly, i.e. within 1 year ("very high" recoverability).
    • The habitat or species is adversely affected by an external factor arising from human activities or natural events (damaged, "intermediate" intolerance) but is expected to recover in a short period of time, i.e. within 1 year or up to 5 years ("very high" or "high" recoverability).
    • The habitat or species is affected by an external factor arising from human activities or natural events (reduced viability **, "low" intolerance) but is expected to take more than 1 year or up to 10 years to recover ("moderate" or "high" recoverability).
    Very low "Very low" is indicated by the following scenarios:
    • The habitat or species is very adversely affected by an external factor arising from human activities or natural events (killed/destroyed, "high" intolerance) but is expected to recover rapidly i.e. within a week ("immediate" recoverability).
    • The habitat or species is adversely affected by an external factor arising from human activities or natural events (damaged, "intermediate" intolerance) but is expected to recover rapidly, i.e. within a week ("immediate" recoverability).
    • The habitat or species is affected by an external factor arising from human activities or natural events (reduced viability **, "low" intolerance) but is expected to recover within a year ("very high" recoverability).
    Not sensitive "Not sensitive" is indicated by the following scenarios:
    • The habitat or species is affected by an external factor arising from human activities or natural events (reduced viability **, "low" intolerance) but is expected to recover rapidly, i.e. within a week ("immediate" recoverability).
    • The habitat or species is tolerant of changes in the external factor.
    Not sensitive* The habitat or species may benefit from the change in an external factor (intolerance has been assessed as "tolerant*").
    Not relevant The habitat or species is protected from changes in an external factor (i.e. through a burrowing habit or depth), or is able to avoid the external factor.
    Insufficient information

    NB: Where there is insufficient information to assess the recoverability of a habitat or species (insufficient information) the precautionary principle will be used and the recovery will be assumed to take a very long time i.e. low recoverability in the derivation of a sensitivity rank.

    The above definitions and scenarios give rise to the decision matrix shown in Table 2. The decision matrix is used to automate the combination of intolerance and recoverability within the MarLIN biology and sensitivity database.

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    The decision matrix shown in Table 2 is not symmetrical because the scale represents scenarios in which the potential damage to the species or habitat matters. The scale is intuitively weighted towards recoverability, although in a few cases intolerances has been given a greater weight rather than under-estimate the potential sensitivity of marine habitats and species.

    Table 2

    Combining 'intolerance' and 'recoverability' assessments to determine 'sensitivity'. NS = not sensitive, NR = not relevant

    Recoverability
    None Very low (>25 yr.) Low (>10/25 yr.) Moderate (>5 -10 yr.) High (1 -5 yr.) Very high (<1 yr.) Immediate (< 1 week)
    Intolerance High Very high Very high High Moderate Moderate Low Very low
    Intermediate Very high High High Moderate Low Low Very Low
    Low High Moderate Moderate Low Low Very Low NS
    Tolerant NS NS NS NS NS NS NS
    Tolerant* NS* NS* NS* NS* NS* NS* NS*
    Not relevant NR NR NR NR NR NR NR

    Please note that the intolerance, recoverability and sensitivity ranks should be read in conjunction with the on-line explanatory rationale for each assessment, which outline the evidence and key information used and any judgements made in the assessment. The information used and evidence collated is fully referenced throughout.

  6. Signing-off. MarLIN reviews are checked by the Programme Director for accuracy and clarity and the required changes made before the review goes on-line on the Website.
  7. Referee. As a final stage in the MarLIN quality assurance, Key Information reviews are subject to peer review by an external marine biologist where possible.

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Assessing the sensitivity of habitats and their associated species (biotopes)


The MarLIN approach to the assessment of the sensitivity of biotopes assumes that the sensitivity of a community within a biotope is dependent upon and, therefore, is indicated by the sensitivity of the species within that community. The species that indicate the sensitivity of a biotope are identified as those species that significantly influence the ecology of that component community (see 'species indicative of sensitivity criteria'). The loss of one or more of these species would result in changes in the population(s) of associated species and their interactions. The criteria used to identify species that indicate biotope sensitivity subdivide species into key and important based on the likely magnitude of the resultant change.

The rationale used to prepare a review of the biology and sensitivity key information for a biotope is given below.

  1. Collate key information on the biotope. The best available scientific information required to describe the ecology and likely sensitivity of the biotope is collated using the resources of the National Marine Biological Library (NMBL), the World Wide Web, and the expertise of marine biologists based at the Marine Biological Association of the UK (MBA), Plymouth.

  2. Select species indicative of biotope sensitivity. Species are selected based on the review of the ecology of habitat and community, where direct evidence of community interaction or dependency is available, or where the species are important characterizing (see 'species indicative of sensitivity criteria' ).

  3. Review key information for the selected species. Key information on the biology and sensitivity of the indicative species is researched (see species sensitivity assessment rationale summary above).

  4. Indicate quality of available data. The MarLIN programme operates an internal quality assurance procedure, to ensure that only the most accurate available information is provided on-line. The quality of the available evidence and our confidence in our assessments (based on availability of information) is clearly stated and ranked against a standard scale (see evidence/ confidence scale).

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  5. Assess the intolerance, recoverability and sensitivity of indicative species to environmental factors. The sensitivity of the indicative species is assessed with respect to change in 24 separate environmental factors (see list of environmental factors). Precedence is given to direct evidence of effect or impact. In the absence of direct evidence, the MarLIN rationale includes simple decision trees to aid intolerance and recoverability assessment based on the available information. The decision trees provide a systematic and transparent approach to assessment. The decision trees are described in full by Tyler-Walters et al. (2001) (see Reports).

  6. Assess overall intolerance and recoverability of the biotope. The intolerance and recoverability of the biotope are derived from the intolerance and recoverability of the species identified as indicative of sensitivity, using a simple procedure shown in Figure 1 for intolerance and in Figure 2 for recoverability. The definitions of biotope intolerance (revised in March 2003) are shown in the relevant glossary.

    Knowledge of the biology of other species in the biotope, especially if they have been researched as a part of the MarLIN programme, is also taken into account.

    Precedence is given to direct evidence of the effects of changes in environmental factors on a habitat, its community and associated species (i.e. the components of a biotope), and its subsequent recovery. The intolerance of a biotope to change in each environmental factor is assessed against a standard benchmark level of effect (view benchmarks), which allows the user to compare the recorded sensitivity to the level of effect predicted to be caused by a proposed development or activity. The evidence and key information used to assess intolerance, recoverability and sensitivity, and any judgements made are explained in the on-line rationale for each assessment. The source of all information used is clearly referenced on-line.

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    Biotope intolerance rationale

    Examples of biotope intolerance assessment ranks derived from species intolerance assessments. The values shown in the table are for demonstration only and do not take into account other Key Information that may affect sensitivity.

    Species that indicate sensitivity Biotope intolerance
    Key structural Key functional Important characterizing Important structural Important functional
    High High Intermediate Intermediate Low High
    High Intermediate Intermediate Low Low High
    Intermediate Intermediate Intermediate Intermediate Intermediate Intermediate
    Intermediate Low High Low Low High
    Low Low Intermediate Low Low Intermediate
    Low Intermediate Low High Intermediate High
    Low Low Low Intermediate Low Intermediate
    Low Low Low Low Low Low
    Low Low N/A N/A N/A Low
    Not sensitive Not sensitive Intermediate N/A N/A Intermediate
    Not sensitive Not sensitive N/A Intermediate High Low

    N/A = No important species identified.

    Biotope recoverability rationale

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  7. Assess sensitivity. The overall sensitivity rank is derived from the combination of intolerance and recoverability using the rationale shown in Table 1 and Table 2.

    The sensitivity assessment rationale uses the question does it matter if?, together with the definitions of sensitive habitats and species proposed in the Review of Marine Nature Conservation (Laffoley et al., 2000) as touch-stones throughout. Due to the importance of recoverability in assessing the continued survival of a habitat or species population, the scale is intuitively weighted towards recoverability. However, where recovery is likely to occur in a short period of time, intolerance has been given a greater weight rather than under-estimate the potential sensitivity of marine habitats and species. The sensitivity scales and definitions are designed to be meaningful in marine environmental management, protection, and conservation.

    For instance, if a habitat or species is very adversely affected by an external factor arising from human activities or natural events (killed/destroyed, high intolerance) and is expected to recover over a very long period of time, i.e. >10 or up to 25 years (low recoverability) then it would be considered to be highly sensitive. Similarly, if a habitat or species is adversely affected by an external factor arising from human activities or natural events (damaged, intermediate intolerance) but is expected to recover in a short period of time, i.e. within 1 year or up to 5 years (very high or high recoverability) then it would be considered to be of low sensitivity. The scenarios used to derive the sensitivity scale are listed in Table 3.

    NB: Where there is insufficient information to assess the recoverability of a habitat or species (insufficient information) the precautionary principle will be used and the recovery will be assumed to take a very long time i.e. low recoverability in the derivation of a sensitivity rank.

    Please note that the intolerance, recoverability and sensitivity ranks should be read in conjunction with the on-line explanatory rationale for each assessment, which outline the evidence and key information used and any judgements made in the assessment. The information used and evidence collated is fully referenced throughout.

  8. Assess the likely effect of the environmental factors on species richness. Change in an environmental factor may not significantly damage key or important species but may still degrade the integrity of the biotope due to loss of species richness. Therefore, the likely effect of the factor on species richness in the biotope is indicated (see species richness glossary)

  9. Signing-off. MarLIN reviews are checked by the Programme Director for accuracy and clarity and the required changes made before the review goes on-line on the Website.

  10. Referee. As a final stage in the MarLIN quality assurance, Key Information reviews are subject to peer review by an external marine biologist where possible.

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References

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