Skip to main content

Is ‘minimising the footprint’ an effective intervention to maximise the recovery of intertidal sediments from disturbance? Phase 1: Literature review

Smyth, K; Mazik, K

Authors

K Smyth



Abstract

Intertidal sediment habitats and the communities they support can be subject to significant physical disturbance resulting from both natural processes and anthropogenic activities (e.g. intertidal fishing activities, construction work and recreational activities). Whilst natural physical disturbance plays a key role in the structuring of soft sediment communities, the need for economic development means that coastal and intertidal areas are under increasing pressure of disturbance from human activities. The ecological and socio-economic importance of intertidal areas necessitates effective management of these pressures to enable economic development without compromising their integrity. Current advice by Natural England is to minimise the impacts of anthropogenic physical disturbance by ensuring that disturbance is localised, accepting that disturbance intensity may be high. That is, a high level of impact over a small spatial area. Whilst there is evidence to suggest that soft sediment habitats and communities will recover following physical disturbance, the processes and timescale for recovery are not well understood, particularly in relation to different disturbance types, scales and intensities. It is hypothesised that the recovery potential of intertidal soft sediment habitats may be increased by increasing the area of impact, thus reducing its intensity, i.e. a low level of impact over a wide spatial area. This study aimed to review the evidence for recovery following different types of physical disturbance in different soft sediment habitats. In general, there was strong evidence to suggest that intertidal soft sediment habitats and their communities have the potential to recover following physical disturbance of varying types and intensities and over varying spatial scales. However, there was a high degree of variability in the definition of recovery between studies and very few studies addressed the potential for recovery of ecological function. Indeed, whilst several methods for determining ecological function exist, many of them are only indicative (few provide a quantitative measure of function) and there is currently no clear guidance on what functions should be measured. With respect to macrofaunal communities, the most widely used interpretation of recovery appears to be comparable species richness, abundance and, in some studies, community structure to pre-disturbance or reference levels. This generally appears to be achievable within 6-12 months (although may be longer where particularly large scale disturbance has taken place). The fastest recovery times were recorded when recovery was allowed to begin coincidentally with the summer larval recruitment period. However, if population structure and biomass are considered, recovery time can be up to five years, or greater. It is of note that this is an important aspect of ecological functioning. Meiofaunal communities generally recover rapidly (based on the definition of recovery provided by individual authors), within hours or days. In contrast, seagrass recovery times of between 2 and >18 years have been reported with poor dispersal ability being a key factor in recovery time. Where permanent habitat changes have taken place (e.g. changes in elevation, sediment composition or hydrodynamic regime), recovery to a pre-disturbance or reference state may be unrealistic. The evidence for recovery following physical disturbance is variable due to: Definition of recovery and the physical/biological parameters used to measure it. The state of the community when the processes of recruitment and colonisation leading to recovery began (total or partial defaunation). This relates to the scale and intensity of disturbance but also to the longevity, fragility and tolerance of the species present. Proximity to undisturbed habitat and a source of adult colonists. Degree of physical modification to the sediment (changes in elevation, particle size, redox gradients, porosity). The level and nature of disturbance experienced by the reference community. That is, how representative is the reference community of undisturbed conditions. The biological feature and the parameters being monitored. In the context of this study, biological features include meiofauna, macrofauna and seagrass. Differences in the scale and source of the disturbance. Recovery times appear to increase with the spatial scale of disturbance although the relationship between scale and recovery is unclear due to variation in the parameters being measured and the point at which recovery is considered to be complete. Temporal variability in community. Some studies showed convergence of community structure and then divergence several months later and variability in the reference community has also been found to imply recovery. However, few studies have compared temporal patterns in recovering and reference communities, or convergence/divergence between the two after the point at which recovery is considered to be complete. The monitoring timescale and frequency which influence the recorded recovery time in that frequent sampling will enable detection of recovery as it happens. In contrast, annual monitoring programmes may only enable detection of recovery several months after it has occurred, potentially giving a false indication of recovery time. The time taken to achieve recovery is habitat and disturbance type (and a combination of both) specific and differences in these parameters between studies mean that the effects of spatial scale and intensity cannot be separated from those associated with habitat, disturbance and experimental design parameters. Overall, there was a broad indication that widespread impacts over large areas and/or high intensity disturbance will lead to prolonged recovery times. However, the variability in the definition of recovery between studies, together with variability between habitats, disturbance types and experimental design, makes it difficult to draw any firm conclusions about the relationship between disturbance scale and intensity and recovery. Furthermore, the timescale of many of the studies reviewed was insufficient to confirm recovery with many studies reporting recovery times of >9 or >12 months (i.e. greater than the duration of the study). Finally, very few studies have replicated the scale and intensity of disturbance associated with construction work where sediment excavation or smothering to depths of tens of centimetres can occur over large areas. Due to the nature of such activities, it might be difficult to minimise the impacts by spreading the disturbance out.

Report Type Research Report
Publication Date Jan 31, 2013
Publisher Natural England
Pages -
Series ISSN 2040-5545
APA6 Citation Smyth, K., & Mazik, K. (2013). Is ‘minimising the footprint’ an effective intervention to maximise the recovery of intertidal sediments from disturbance? Phase 1: Literature review. England: Natural England
Publisher URL http://publications.naturalengland.org.uk/file/5078414
;