2007; Mander et al. , 2007; Elliot, 2015). The community may change after facilitating tidal exchange, compared to what it was before. For example, at Osaka Port, Japan, the number of shorebirds increased five-fold after tidal introduction on reclaimed land (Natuhara et al ., 2005), with ducks (e.g. Common Pochard Aythya ferina ) being replaced by plovers (Charadriidae) and sandpipers (Scolopacidae). Habitat preference may differ among species. For example, at a restored site in California, USA, Willet Catoptrophorus semipalmatus and dowitchers ( Limnodromus spp). preferred extensive tidal flats, while godwits ( Limosa spp.) and sandpipers ( Calidris spp.) preferred habitats with a mix of water and tidal flats (Armitage et al. , 2007). Note that there may be a trade-off when creating habitat for birds, between breeding and foraging space. Effect on invertebrates: Macrobenthic invertebrates can colonise quickly, with biomass densities reaching similar levels to those in comparable areas of 'natural' tidal flat within two to five years (Mazik et al. , 2010; Malcom Ausden, pers. comm.), but it can take decades for the community structure to fully develop (Craft & Sacco, 2003; Reading et al. , 2008). In a restored tidal flat in Osaka, Japan, chironomids were replaced by polychaetes and gammarids after reinstating tidal flow, and there were fewer brachyurans and molluscs compared to natural tidal flats in Japan (Natuhara et al., 2005). The time taken for invertebrates to reach natural levels will depend on the characteristics of the species and their requirements. For example, in created marshes in North Carolina, USA, species with dispersing larval stages reached natural levels within three years, while earthworms (oligochaetes) took 25 years to reach densities similar to natural marshes (Craft & Sacco, 2003). Effect on vegetation : In many cases where tidal exchange has been facilitated (and where areas were of a suitable elevation), vegetation characteristic of salt marshes develops within one to two years (Barrett & Niering, 1993; Dagley, 1995; Brockmeyer et al. , 1996; Burdick et al. , 1996; Roman et al. , 2002; Thom et al. , 2002; Williams & Orr, 2002; Badley & Allcorn, 2006; Garbutt & Wolters, 2008; Wolters et al. , 2008; Hughes et al. , 2009; Howe et al. , 2010; Mossman et al. , 2012; Rochlin et al. , 2012; Elliot, 2015; Chang et al. , 2016; Flitcroft et al. , 2016; Clifton et al. , 2018). However, the vegetation community of restored areas may remain different from natural salt marshes after more than 30 and 50 years (Elphick et al. , 2015; Flitcroft et al. , 2016). In some cases, facilitation of tidal exchange is followed by little or no change in the amount of vegetation for up to four years (Buchsbaum et al. , 2006; Konisky et al. , 2006; Kadiri et al. , 2011).
3. Factors that can affect outcomes
Site area : Before facilitating tidal exchange, the amount of space available for intertidal habitat needs to be considered. If infrastructure is too close to the coast, new intertidal habitat and its associated wildlife will have limited space to develop behind the breached defences (Howe et al. , 2010; Morris, 2013). The size (and isolation) of a restoration site may also influence the species that establish there. Small sites may never develop the full range of biodiversity that is seen in large natural sites (Atkinson et al. , 2004; Wolters et al. , 2005). One review found that the highest species diversity occurred in sites over 100 ha (Wolters et al. , 2005). At a site in Japan, the population of large sandpipers and snipe (Scolopacidae) decreased even after the enlargement of the tidal flat and it is speculated that the area (2.6 ha) was too small for these species (Natuhara et al. , 2005).
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