Saltmarsh erosion and management of saltmarsh restoration; the effects of infaunal invertebrates

Abstract

1. Loss of saltmarshes in SE England poses significant problems for conservation and for flood defence. The functioning of internationally important estuarine habitats is at risk and the loss of vegetation which protects sea walls is potentially expensive. 2. Managed realignment, where some sea walls will be allowed to fail, or breached deliberately, in the expectation that saltmarsh will develop behind the sea wall, could ameliorate both problems. 3. This paper questions whether managed realignment will lead to saltmarsh development when established saltmarshes are eroding. The processes operating behind two unmanaged breaches are examined, one where saltmarsh did not develop, and an older site where saltmarsh developed but has eroded since. 4. The data indicate that herbivory and bioturbation by the invertebrate infauna, particularly Nereis diversicolor and Corophium volutator are responsible, at least in part, for the loss of saltmarsh vegetation, particularly in the pioneer zone. 5. A hypothesis is proposed to relate the losses of saltmarshes in SE England over the past four decades to the activities of the infauna, particularly N. diversicolor, which some evidence indicates has increased in range and abundance over the same time‐scale. 6. Development of saltmarsh, in managed realignment sites and elsewhere, may not occur without management to reduce the effects of the infauna. Copyright © 1999 John Wiley & Sons, Ltd.

The effects of the polychaete Nereis diversicolor on the distribution and transplanting success of Zostera noltii

“…Beukema 1989;Jensen 1992), but also in the estuaries of south-east England (Hughes 1999). Hughes and Gerdol (1997) found Nereis in 93% of the sites examined in the estuaries of the Crouch and the Blackwater.…”

“…They partially emerge from their burrows to engulf sediment and larger particles, including plant material, before withdrawing into their burrows (Olivier et al 1996). Hughes (1999) considered the possibility that Nereis has increased in abundance over the past few decades, as it has in the Wadden Sea (e.g. Beukema 1989;Jensen 1992), and consequently may have had, and may continue to have, an effect on the ecology of these systems, including the potential to reduce colonisation of mud by pioneering plants.…”

The effects of bioturbation and herbivory by the polychaete Nereis diversicolor on loss of saltmarsh in south‐east England

“…There is some evidence that Nereis has increased in abundance over the past few decades (Hughes 1999), and the accelerated creek erosion identified here and linked to its presence may also be similarly recent in extent. Export of sediment from the creeks may entrain a positive feedback as the increase in floodable volume leads to increased current speeds, especially at the seaward end of long creek systems, and hence to further erosion.…”

“…The natural response of marsh vegetation to sea level rise is upward inland migration, but this is prevented by the sea walls and consequently the saltmarsh habitat is lost by being squeezed between the rising sea level and the hard sea defences (Boorman 1992; Burd 1992; English Nature 1992; Turner 1995). However, Hughes (1999, 2001) could find no evidence to support the coastal squeeze hypothesis, and enquiries and searches of the relevant unpublished reports during this study also failed to uncover any evidence. Hughes (1999, 2001) and Hughes et al .…”

“…However, Hughes (1999, 2001) could find no evidence to support the coastal squeeze hypothesis, and enquiries and searches of the relevant unpublished reports during this study also failed to uncover any evidence. Hughes (1999, 2001) and Hughes et al . (2000) developed alternative hypotheses for recent marsh erosion based upon bioturbation and herbivory by the infauna at the saltmarsh–mudflat interface.…”