Mudflats - Introduction

Mudflats form in sheltered areas in the intertidal zone, where fine sediment particles such as clay or silt (<0.125mm) will accumulate due to calmer waters with less energy and movement. Mudflats are a typical habitat of estuaries and sheltered bays, and are a wide, level, open habitat which can appear to have a 'watery sheen' even when the sea is at low tide (fig. 1). Mudflats often transition into other habitats when succession occurs, such as saltmarsh. (Lake et al, 2015). 

The UK has over 580,000 ha of 'estuarine resource', of which 270,000 ha is intertidal flats (mud and/or sand). It is estimated that the UK hosts around 15% of the North-West European estuarine habitat (BRIG, 2011). One key area for intertidal mudflats on the East Grampian coast is the Ythan Estuary. 

Biodiversity:
Mudflats are not species-rich, i.e. there are a lower number of species which exist in mudflat environments, but they are highly biologically productive and abundant areas with a high density of individual organisms (BRIG, 2011; Lake et al, 2015). For example, it is estimated that 1 cubic metre of mudflats could contain over 1000 worms (Lake et al, 2015). The diversity of species is influenced by a number of factors including salinity levels, softness of sediment, and levels of sand vs mud (i.e. is it a sandy mud or a muddy sand that makes up the intertidal flat). 

Mudflats are a key area for invertebrates such as polychaete worms, bivalves, and mud snails. This is turn provides a food source for waders and wildfowl such as curlew (Numenius arquata) (fig. 2), shelduck (Tadorna tadorna), eider (Somateria mollissima). As such, mudflats and estuaries can  be key feeding and resting areas for internationally important populations of migrating and/or wintering waders and wildfowl. Mudflats can also provide nursery areas for species such as flatfish (BRIG, 2011; Lake et al, 2015).

Ecosystem Services:
(Austen et al, 2011; BRIG, 2011; Lake et al, 2015; Lebreton et al, 2019)
Mudflats provide a number of ecosystem services, following the four classifications introduced in the Millenium Ecosystem Assessment (2005).

Supporting: Mudflats can support primary production through micro-algae. Invertebrates in mudflays will carry out nutrient cycling through feeding, burrowing, and irrigation activity.

Provisioning: Mudflats can provide fish and shellfish for consumption and also for use as bait. Mudflats provide habitat for invertebrates and birds.

Regulating: One key ecosystem service that mudflats provide is hazard regulation and coastal protection Mudflats can dissipate wave energy, and therefore reduce coastal erosion and flooding. Mudflats often provide a first line of defence from the sea, and their absorption of wave energy can also protect saltmarsh and other coastal habitats from erosion.

Cultural: Mudflats, and wider estuaries, are important as a source of education and scientific study, an area for recreation (e.g. walking), an area for welbeing (meaningful space, exercise), and as a source of inspiration for art. 

Conservation Status:
Intertidal Mudflats are a Priority Marine Habitat on the UK Biodiversity Action Pland and Scottish Biodiversity List ((BRIG, 2007; NatureScot, 2020).