Increasing roughness • Invertebrate exclusion mats

Increasing roughness

In an attempt to combat erosion, enhancing the bed roughness has also been attempted using artificial seaweed. This consists of polypropylene fronds attached at one end to a geotextile mat which is anchored to the seabed. However, this has been largely unsuccessful due to the difficulties of attaching the mats to the unstable bed under breaking wave conditions.

Other techniques to increase surface roughness have included seeding mudflats with mussel sprats. Further information on this subject is provided in Soft engineering techniques for high and low energy coasts produced by UK-CHM (Defra and JNCC). The full report can be downloaded at www.chm.org.uk/library/ecosys/marine/ETMC001.pdf.

Invertebrate exclusion mats

Recent research by Hughes and Paramour (2004) has demonstrated that saltmarsh accretion and colonisation of pioneering species can be promoted by removing invertebrates using mulch mats. In particular, they discuss the effects of the polychaete worm, Nereis diversicolor, in terms of sediment instability (through burrowing) and herbivory (feeding on Salicornia spp seeds). They also suggest that the decline in recent years of the seagrass Zostera spp. may also contribute to saltmarsh erosion and suggest that sea grass beds could be transplanted to dissipate wave energy.