Biodiversity & Conservation

Sensitivity assessment ‘READ ME’ – Notes for interpretation

The following is a short summary of the key assumptions involved in MarLIN sensitivity assessments and notes on their interpretation. Information on the development of the sensitivity assessment approach is detailed in Hiscock et al. (1999) and Tyler-Walters & Jackson (1999), the full approach is outlined in Tyler-Walters et al. (2001) and, as revised in 2003, on the MarLIN Website (see the 'sensitivity assessment rationale').

Introduction

Marine organisms may be affected by a number of human activities and natural events. The magnitude or scale of the effect of an activity (or event) is dependent on the receiving environment. The same activity (or event) in different locations may have different effects. For example, an activity that markedly increased siltation may have little effect in a turbid estuary whereas it would probably have significant effects in a sheltered embayment. Therefore, the effects of an activity and the resultant change in environmental factors are site specific and cannot be generalised.

In addition, any one activity (or event) may change one or more environmental factors (see ‘effects of specified marine and coastal activities or natural events’). Similarly, it is not possible to take into account every set of environmental conditions to which a species or biotope are exposed throughout their range.

In order to achieve a practical, systematic, and transparent approach, the assessment of intolerance, recoverability, and sensitivity required a standard set of definitions and scales (see ‘sensitivity assessment rationale summary’). The assessment of intolerance required a specified level of environmental perturbation. Therefore, the MarLIN programme developed a set of ‘benchmark’ levels of environmental change in the environmental factors against which to assess sensitivity. The benchmarks also allow intolerance and hence sensitivity to be compared against the predicted effects of planned projects or proposals (see the ‘sensitivity assessment benchmarks’).

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Sensitivity assessment

Sensitivity assessments and key information reviews are designed to provide the information required to make scientifically based environmental management decisions. It is not possible for sensitivity assessment to consider every possible outcome and is indicative. MarLIN sensitivity assessments are indicative qualitative judgements based on the best available scientific information. They do not allow quantitative analysis. The sensitivity assessment represent the most likely (or probable) result of a given change in an environmental factor on a species population or biotope.

Sensitivity assessments require expert interpretation on a site-by-site or activity-by activity basis. MarLIN sensitivity assessments should be read in conjunction with the explanation and key information provided, together with the relevant benchmark. In all cases, an explanation of each intolerance, recoverability and hence sensitivity assessment is provided, together with a summary of the relevant key information, and references highlighted.

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Assumptions

The following decisions and assumptions are inherent in the MarLIN approach to sensitivity assessment.

The intolerance, recoverability, and sensitivity of a species or biotope to a specified level of environmental perturbation are dependent on the biology of the species or ecology of the biotope.
Intolerance, and hence sensitivity, depends on the magnitude, duration, or frequency of change in a specific environmental factor.
The effects of an activity or natural event and the resultant change in environmental factors are site specific and cannot be generalised. Therefore, a series of standard level of effect or change in each environmental factor are used for assessment (the benchmarks).
MarLIN sensitivity assessments are not site specific. The intolerance of a hypothetical ‘average’ species population is assessed, representing a population in the middle of its range or habitat preferences. Populations at the limits of their environmental preferences are likely to be more intolerant of environmental perturbation.
Recoverability assumes that the impacting factor has been removed or stopped and the habitat returned to a state capable of supporting the species or biotope in question. The time taken for the habitat to return to a state capable of supporting the species or biotope is not assessed.
Where the collated key information and other evidence suggests a range of intolerances or recoverabilities, a precautionary approach is taken, and the ‘worst case’ scenario, i.e. the higher sensitivity, is reported.
In all cases, the explanation behind each sensitivity assessment, the relevant key information and references are highlighted.

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Interpretation of sensitivity assessments

Sensitivity is based on the assessment of intolerance against a benchmark level of change in an environmental factor, and the likely recoverability of the species population or biotope.

The benchmarks are intended to be pragmatic guidance values for sensitivity assessment, to allow comparison of sensitivities between species, and to allow comparison with the predicted effects of project proposals.
Species or biotopes are likely to be more intolerant, and hence potentially more sensitive, to any activity or natural event that causes a change in a specific environmental factor of greater magnitude and/or longer duration and/or greater frequency than the benchmark. For example:
- if the predicted change in an environmental factor has a greater magnitude than that used in the benchmark, then it is likely that the species population / biotope will have a greater sensitivity to this change;
- if the predicted change in an environmental factor has a longer duration than that used in the benchmark, then it is likely that the species population / biotope will have a greater sensitivity to this change;
- if the predicted change in an environmental factor is likely to occur at higher frequency than used in the benchmark, then it is also likely that the species or community will exhibit a higher sensitivity;
- if the frequency of the predicted change in an environmental factor is greater than the time required for recover then the species or community will probably exhibit a higher sensitivity,
- while if the species or community is likely to recover between the impacting events then it may not exhibit an increased sensitivity.
Similarly, if a species population is isolated from sources of recruitment, for instance in isolated water bodies (e.g. sea lochs or lagoons) or by hydrography, then the recoverability may lower, and hence the population may exhibit a higher sensitivity. Isolation is already factored into the recoverability assessments for relevant biotopes and lagoonal species.

Activities that result in incremental long term change, such as climate change, are difficult to assess since the given level of change varies with time. Synergistic and antagonistic effects are also difficult to predict and are poorly understood, especially for pollutants. These effects have not been addressed within the sensitivity assessments. However, benchmarks could be compared to the predicted level of change at specific time intervals.

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