creation may already see birds using it if the required vegetation cover (ranging from none to substantial, depending on the target species) has been achieved (see Cutts et al., 2024a). For feeding habitat, the created tidal flat needs to have been able to build up a population of invertebrates before the birds can start feeding on them, which may require a colonisation interval (Evans et al ., 1999). Invertebrates : Macrobenthic invertebrates can colonise created tidal flats and reach similar overall abundance to that of natural tidal flats. For example, a study in Ago Bay, Japan, saw similar or even higher biomass of macrobenthic fauna develop over a 20-month period compared to nearby natural tidal flats. In Moune Bay, Japan, restored tidal flats (following an earthquake and tsunami) were found to be inhabited by a diverse and abundant benthic fauna dominated by juvenile clams within 14 months (Chiba et al. , 2015). However, sometimes it may take decades for the community structure to fully develop to a ‘natural’ state (Craft & Sacco, 2003; Bolam et al. , 2006; Reading et al. , 2008). Polychaetes are typically among the first pioneers to colonise; they are habitat generalists (Diaz-Castañeda & Reish, 2009) but species in later successional stages can vary as their responses to disturbance differs (Zajac & Whitlatch, 1982) and may vary depending on differences between the existing sediment and the added dredged sediment (Imai et al. , 2008; Ishii et al. , 2008; Nasser et al. , 2019). A study in the UK that noted late colonisation of invertebrates suggested that it was due to too much compaction of the earth caused by heavy machinery (Evans et al. , 1999). The dispersal capacity of the species will influence the time taken for colonisation of a new site (Craft & Sacco, 2003). Vegetation : Salt marsh vegetation can develop naturally on dredged sediment, but the time taken has shown to vary among sites. For example, in Louisiana, USA, some salt marshes were created by pumping dredged sediment into open water (Edwards & Proffitt, 2003). The created marshes were colonised from nearby natural marshes, but it took between 4 and 17 years for the vegetation community to reach similarity to natural marshes. In South Carolina, USA, LaSalle et al. (1991) found that vegetation biomass on areas of deposited sediment reached similar levels to that of natural marshes within four years. Further research in South Carolina showed that it took between 6 and17 years for monospecific stands of vegetation to develop on areas of deposited sediment, with a minimum of 13 years for mixed communities to develop (Alphin & Posey, 2000). The vegetation community that develops on created marshes may be different from natural marshes, as Edwards & Proffitt, (2003) found in one of their sites, where the plant community was different eight years after creation.
3. Factors that can affect outcomes
Sediment characteristics : Differences in sediment composition (e.g. grain size and organic:inorganic ratio) can affect how biodiversity develops and manifests. For example, using coarser sediment, or compacted sediment, can affect its suitability for benthic invertebrates (Evans et al. , 1999; Peterson et al. , 2006), and can make it more difficult for vegetation to establish (if the goal is to create a salt marsh) (Haltiner et al. , 1996). A pilot study creating two artificial tidal flats at mesocosm scale (3.6 m 2 ) in a tidal flat simulator in Japan, found that increasing the percentage of silt and clay increased the emerging number of macrobenthos (Ishii et al. , 2008). An experiment in the UK found that a higher organic content
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