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 mudflats are shallow reflecting the low energy conditions. Microbial activity has a valuable role in stabilising estuarine organic fluxes by reducing the seasonal variation in primary production, ensuring a relatively more-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).

The presence of high densities of adult invertebrates may inhibit the recruitment of potential colonising stages (planktonic larvae) from the water column (Olafsson, Peterson & Ambrose 1994). This may account for juveniles occupying less favourable parts of the intertidal areas, for example juvenile Arenicola and Nephtys settle in areas outside the optimal distribution for the adults. Mudflats are important nursery areas for plaice (Lockwood 1972; Marshall 1995; Marshall & Elliott 1997).

Intertidal mudflats are important in the functioning of estuarine systems and may have a disproportionately high productivity compared to subtidal areas (Elliott & Taylor 1989). Estuarine mudflats receive primary production from benthic microalgae and water-column phytoplankton but production may be light-limited in these turbid environments.

None.

Intertidal areas are well defined as juvenile fish-feeding areas (Costa & Elliott 1991). The most important marine predators on intertidal mudflats 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. of Arenicola and Nereis), bivalve young and siphons (e.g. of Macoma) (Croker & Hatfield 1980; McDermott 1983; McLachlan 1983). In summer, large numbers of juvenile plaice and dab move over flats at high tide to feed on mobile epifauna, sedentary infauna and protruding siphons and tentacles (Elliott & Taylor 1989). Within estuaries and on mud, however, many demersal fish are opportunistic predators and the prey choice will reflect the infaunal species distribution of the area (Costa & Elliott 1991).

The littoral mud habitat is 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). Migratory species of fish such as salmon and shad can be found on mudflats when on passage to other wetlands e.g. saltmarshes and freshwater areas, although they appear to have no requirement for the mud and sandflats

No information available.

No information available.

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