MarLIN (1999-2010) sensitivity assessment methodology

Note - the MarESA approach supersedes and replaces the MarLIN approach but while MarLIN sensitivities remain online, the following explanation is provided for reference.

The MarLIN 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). 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 was 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 the 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' is 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, the 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.

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 the cessation of 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 the quality of available data. 

The MarLIN programme operates an internal quality assurance procedure, to ensure that only the most accurate available information is provided online. The quality of the available evidence and our confidence in our assessments (based on the 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 or experiments that looked at the effect of the specific factor on the species, or targeted work or 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.

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).

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 the 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 online.

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 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 Table1.

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.
No information  No relevant information (or data) was found or the information was insufficient for an assessment to be made. 

Note: where there is insufficient information (or data) 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.

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, intolerance has been given more 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
Sensitivity Recoverability
Intolerance None Very low
(>25 yr.)		 Low
(>10/25 yr.)		 Moderate
(>5 -10 yr.)		 High
(1 -5 yr.)		 Very high
(<1 yr.)		 Immediate
(< 1 week)
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

Note: the intolerance, recoverability and sensitivity ranks should be read in conjunction with the online explanatory rationale for each assessment, which outlines the evidence and key information used and any judgements made in the assessment. The information used and the 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 are made before the review goes online 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.

Assessing the sensitivity of 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 the quality of available data. 

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

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 publications).

6. Assess the 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 below for intolerance and recoverability. The definitions of biotope intolerance (revised in March 2003) are shown in the relevant glossary. Knowledge of the biology and likely sensitivity of other species in the biotope is also taken into account, especially if they have been researched as a part of the MarLIN programme.

The procedure to derive biotope intolerance based on indicative species intolerance. 

  1. Are any key structural or key functional species intolerant of the factor?
    • If yes, go to 2
    • If not, go to 3
  2. Do these species have a 'High' intolerance to the factor?
    • If yes, record a biotope intolerance assessment of 'High' intolerance
    • If not, go to 3
  3. Do the important characterizing species have a 'High' intolerance to the factor?
    • If yes, record a biotope intolerance assessment of 'High' intolerance
    • If not, go to 4
  4. Are important structural or important functional species more intolerant of the factor than the above species?
    • If yes, record a biotope intolerance assessment of one rank higher (more intolerant) than the key or important characterizing species
    • If not, go to 5
  5. Are the important structural or important functional species of less or equal intolerance of the factor than the above species?
    • If yes, record a biotope intolerance assessment equal to that of the key or important characterizing species, and move to step 6
  6. Review other key information that may affect intolerance to the factor e.g., ecological relationships between species, habitat complexity, substratum preferences or hydrographic conditions). 
  7. Modify the intolerance assessment based on step 6 if necessary. 

The procedure to derive biotope recoverability based on indicative species recoverability.

  1. Are any key structural or key functional species likely to recover immediately?
    • If yes, go to 3
    • If not, go to 2
  2. Do these species have a 'Very low' recoverability to the factor?
    • If yes, record a biotope recoverability assessment of 'Very low'.
    • If not, go to 3
  3. Do the important characterizing species have a 'Very low' recoverability to the factor?
    • If yes, record a biotope intolerance assessment of 'Very low'.
    • If not, go to 4
  4. Are important structural or important functional species likely to take longer to recover from the factor than the above species?
    • If yes, record a biotope recoverability assessment of one rank lower (slower recovery) than the key or important characterizing species
    • If not, go to 5
  5. Are the important structural or important functional species of less or equal recoverability from the factor than the above species?
    • If yes, record a biotope recoverability assessment equal to that of the key or important characterizing species, and move to step 6
  6. Review other key information that may affect recoverability from the factor e.g., ecological relationships between species, habitat complexity, substratum preferences or hydrographic conditions. 
  7. Modify the recoverability assessment based on step 6 if necessary. 

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 the 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 online rationale for each assessment. The source of all information used is clearly referenced online.

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.

Note: 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 online explanatory rationale for each assessment, which outlines the evidence and key information used and any judgements made in the assessment. The information used and the evidence collated is fully referenced throughout.

8. Assess the likely effect of 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 are made before the review goes online on the website.

10. Referee. 

As a final stage in the MarLIN quality assurance, biology and sensitivity reviews are subject to peer review by an external marine biologist where possible.

Bibliography

Note all MarLIN reports are available under publications.

  1. Hiscock, K, Jackson, A. & Lear, D., 1999. Assessing seabed species and ecosystem sensitivities: existing approaches and development, October 1999 edition. Report to the Department of Environment, Transport and the Regions from the Marine Life Information Network (MarLIN). Marine Biological Association of the United Kingdom, Plymouth. [MarLIN Report No. 1.]
  2. Holling C.S., 1973. Resilience and stability of ecological systems. Annual Review of Ecology and Systematics, 4(1), 1-23.
  3. Holt, T.J., Jones, D. R., Hawkins, S.J. & Hartnoll, R.G., 1997. The sensitivity of marine communities to man-induced change. Nature Conservation and the Irish Sea seminar. 6th February 1997, pp. 6-23. Irish Sea Forum, Liverpool, Seminar Report No. 15.
  4. Holt, T.J., Jones, D.R., Hawkins, S.J. & Hartnoll, R.G., 1995. The sensitivity of marine communities to man-induced change - a scoping report. Countryside Council for Wales, Bangor, CCW Contract Science Report, No. 65.
  5. Laffoley, D.A., Connor, D.W., Tasker, M.L. & Bines, T., 2000. Nationally important seascapes, habitats and species. A recommended approach to their identification, conservation and protection, pp. 17. Peterborough: English Nature.
  6. Mainwaring, K., Tillin, H. & Tyler-Walters, H., 2014. Assessing the sensitivity of blue mussel beds to pressures associated with human activities. Joint Nature Conservation Committee, JNCC Report No. 506., Peterborough, 96 pp. 
  7. McMath, A., Cooke, A., Jones, M., Emblow, C.S., Wyn, G., Roberts, S., Costello, M.J., Cook, B. & Sides, E.M., 2000. Sensitivity mapping of inshore marine biotopes in the southern Irish Sea (SensMap): Final report. Report by the Countryside Council for Wales (CCW), Ecological Consultancy Services Ltd (Ecoserve), Dchas, the Heritage Service, 116 pp. [Maritime Ireland /Wales INTERREG Reference no. 21014001].
  8. Oakwood Environmental Ltd, 2002. Development of a methodology for the assessment of cumulative effects of marine activities using Liverpool Bay as a case study. CCW Contract Science Report No 522.
  9. OSPAR, 2003. Annex V to the OSPAR Convention. Criteria for the Identification of Species and Habitats in need of Protection and their Method of Application (The Texel-Faial Criteria). OSPAR 03/17/1-E.   13 pp. 
  10. OSPAR, 2008. OSPAR List of Threatened and/or Declining Species and Habitats (Reference Number: 2008-6). OSPAR Convention For The Protection Of The Marine Environment Of The North-East Atlantic <http://www.jncc.gov.uk/pdf/08-06e_OSPAR%20List%20species%20and%20habitats.pdf>
  11. Tyler-Walters, H., Hiscock, K., Lear, D.B. & Jackson, A., 2001. Identifying species and ecosystem sensitivities. Report to the Department for Environment, Food and Rural Affairs from the Marine Life Information Network (MarLIN), Marine Biological Association of the United Kingdom, Plymouth. Contract CW0826.
  12. Tyler-Walters, H. & Jackson, A. 1999. Assessing seabed species and ecosystems sensitivities. Rationale and user guide, January 2000 edition. Report to English Nature, Scottish Natural Heritage and the Department of the Environment Transport and the Regions from the Marine Life Information Network (MarLIN). Plymouth, Marine Biological Association of the UK. (MarLIN Report No. 4.).