Intertidal areas by definition have low, middle and high tidal heights and the productivity of these areas differs with respect to the tidal elevation and shore slope (Gray 1981). Most of the infaunal community is found in the mid-tidal region, with any decrease in tidal height taking the area towards greater current speed near channels and any increase in height will result in greater exposure to air and thus desiccation of the organisms. Changes in tidal height over the intertidal zone create a less predictable environment where there may be more extreme changes in temperature, salinity, dissolved oxygen and water content than in the sublittoral zone (Hayward 1994). The gradient of the shore reflects the energy conditions – that of muddy sands being gently-sloping and reflecting low-medium energy conditions. Microbial activity has a valuable role in stabilising estuarine organic fluxes by reducing the seasonal variation in primary production, ensuring a relatively constant food supply, and allowing the re-absorption of dissolved nutrients. (Robertson 1988). The bacteria living on particulate or dissolved organic matter makes the primary production more readily available for animal consumption (McLusky 1989).Intertidal sandflats also support microphytobenthos in the interstices of the sand grains. Mucilagenous secretions produced by these algae may stabilise fine substrata (Tait & Dipper 1998). Macrophytes of intertidal sand are few unless there are some stones or shells for attachment. The community may include mats of Enteromorpha and Ulva, possibly in large aggregations to form so-called ‘green tides’ (Piriou, Menesguen & Salomon 1991).

The presence of high densities of adult invertebrates may inhibit the recruitment of potential colonising stages from water (Olafsson, Peterson & Ambrose 1994). This may account for juveniles occupying less favourable parts of the intertidal areas, for example juvenile Arenicola settles in areas outside the optimal distribution for the adults.

Coastal mudflats have a very poor productivity (McLachlan 1983).

None.

Intertidal areas are well defined as juvenile fish feeding areas (Costa & Elliott 1991). Sandflats are important nursery areas for plaice (Lockwood 1972; Marshall 1995; Marshall & Elliott 1997), as well as feeding areas for sea bass and flounder (Elliott & Taylor 1989). Fish such as sole Solea solea and gadoids frequent sandy areas, but many also occur on coarser and mixed grades of sediment. The most important marine predators on intertidal sandflats are the flatfish sole Solea solea, dab Limanda limanda, flounder Platichthys flesus and plaice Pleuronectes platessa which feed on polychaetes and their tails (e.g. Arenicola), bivalve young and siphons (e.g. of Macoma and Angulus) and tidally active crusteaceans such as Bathyporeia and Eurydice species (Croker & Hatfield 1980; McDermott 1983; McLachalan 1983). In summer, large numbers of plaice and dab juveniles move over the sand at high tide to feed on mobile epifauna, sedentary infauna and protruding siphons and tentacles (Elliott & Taylor 1989). The muddy sand biotopes are used by important wintering and passage birds for feeding and roosting. Shorebirds form important predators on north-west European intertidal mudflats during long migrations over long distances from breeding to wintering grounds. Particularly dependant species are Brent geese, shelduck, pintail, oystercatcher, ringed plover, grey plover, bar-tailed and black-tailed godwits, curlew, redshank, knot, dunlin and sanderling, whilst grey geese and whooper swan may use this habitat for roosting (Jones & Key 1989; Davidson et al. 1991). In comparison to mudflats, muddy sands tend to support a more extensive bird population.

No information available.

No information available.

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