MUDFLATS, ESTUARIES AND SALTMARSHES
To the unenlightened eye, estuaries and mudflats may seem like featureless expanses of mud and little else. However, the vast numbers of birds that feed on these habitats during the winter months testify to their unseen productivity and the extraordinary diversity of invertebrate life they support.
BENEATH THE SURFACE
Evidence for the wealth of marine life found in mudflats and estuaries is not always easy to detect, although worms casts and the carpet of small marine molluscs on the surface hint at the productivity in the mud itself. In fact, incredible numbers of invertebrates do thrive in the oozing substrates that make up our estuaries and mudflats, their numbers supported by the organic matter deposited when river meets sea. Lugworm and ragworm species are typical representatives of their kind, while marine molluscs include various species of cockles, clams and other bivalves, as well as minute but abundant Laver Spire Shells.
Lugworm casts at Budle Bay, Northumberland. Home to internationally important concentrations of waders and wildfowl in winter, Britain’s estuaries and mudflats are among the finest in the world. Vast numbers of invertebrates live buried beneath the surface in the treacherous sediment.
ESTUARY BIRDLIFE
It is between autumn and spring that estuaries and mudflats come into their own in terms of birdlife. During the summer months, many of the species so familiar on our estuaries in winter are nesting elsewhere, many in the Arctic. But once breeding is complete, they return to our estuaries in autumn.
Outside the breeding season, waders are the most characteristic group of estuary birds. Each species has a bill length and feeding strategy adapted to suit a particular food source and this helps reduce feeding competition. Wildfowl are also present in good numbers: Shelduck filter minute animals from the mud with their bills, while Brent Geese and Wigeon favour plant material.
Curlews use their long, curved bills to probe the soft mud for invertebrate prey, particularly juicy Lugworms.
SALTMARSHES
During the winter months, most estuaries are positively dreary in botanical terms, studded with a mosaic of bedraggled-looking vegetation and very little else. But come the summer months, the upper reaches of the mudflats – those areas least affected by the tides – come to life. Specialist salt-tolerant plants colonise and stabilise the oozing mud, creating saltmarsh. Able to cope with twice-daily inundation by sea water, these colonisers include species of glasswort and sea-lavender, as well as Sea Purslane and Annual Sea-blite.
A colourful saltmarsh community on the north Norfolk coast in July, with abundant Common Sea-lavender.