Merse-bergs and Mudshrimps

The samphire, Salicornia, looked grey and wizened, worn down by the winter and there were still traces of snow on Criffel’s northern slope. It was a cold, windy day in March on the Solway Firth, and I was heading out onto the merse and mudflats of the River Nith with Adam Murphy and Andy Over, both Reserve Officers at Caerlaverock National Nature Reserve. We were on an ‘expedition’ to look for Mudshrimps, Corophium volutator, at Scar Point, on the east bank of the River Nith. The Point is also known as Fishermens’ Bush (it’s a favoured spot for fishing when the tide flows in) or even Phyllis’s: Phyllis Laurie, who died in 1942 at the age of 72, lived nearby and according to the Solway Firth Partnership’s little booklet Tide Islands and Shifting Sands, was a “character” who was “feared by local children”. She owned a horse and cart, and the story has it that if she became incapable of driving after visiting the pub on a Saturday night, the horse always knew its way home. Phyllis might be pleased that the Point has been given her name – but perhaps less impressed that her name also distinguishes a nearby creek across the mud.

Footsteps

Adam, in his thirties and with a reddish-brown beard, strode out onto the merse, and Andy – older, shaven-headed, recently arrived at Caerlaverock from ten years with SNH on Harris – kindly held out a hand whenever creek-jumping required longer legs than mine. As we walked across the merse Adam pointed out the partly-exposed gnarly rhizomes of sea-aster, the fleshy spikes of arrow-grass and the shiny leaves of two species of scurvy grass,  amongst the thin film of sediment on the short ‘turf’ of salt-tolerant Pulcinellia.

When poet Norman Nicholson wrote about the saltmarshes on the Solway’s English coast in the 1940s, he was writing during a time when iron-ore smelting and steel-making around Workington were important parts of the West Cumberland economy. He was attracted to the marshes even when “as around Workington and Maryport, they are soiled and smeared by smoke and scum from the iron and steel works.” The residues of industry affected even the white flowers of scurvy-grass – “Many people despise this plant, perhaps because … it gets clogged with coal-dust as in Workington Harbour, or with red ore-dust in the iron country.” Those industries are long-gone and in March the scurvy-grass flowers were “a welcome mass of white”, and the surfaces of the saltmarshes unsullied. Adam told me that sailors used to eat it as a source of vitamin C. Norman Nicholson noted, “It must have been nearly as unappetising as boiled cabbage” (1)

We found otter spraint, glittering with fish-scales, and discussed whether it smelled of violets (it did not, but was not unpleasant); and wind-blown mermaids’ purses, the square matt-black egg-cases of the Thornback Rays which are common in the Firth. The north-westerly wind was ferocious and cold, blowing our words away and tearing the pages of my notebook. Five Pink-footed Geese came beating across the flats, heading slowly into the wind, their wingtips almost touching the mud. The edge of the merse was ragged and unfocussed, a perfect example of the estuary’s give-and-take. Little troops of samphire had boldly marched out during the previous summer, and had gathered new ground around themselves before losing heart and shrivelling.

Just beyond the saltmarsh’s edge the mudflat was stippled with tiny holes, and conical mounds of mud, a couple of millimetres high, betraying the openings of the Mudshrimps’ burrows. I dug the spade into the mud and lifted it gently so that the divot of mud broke apart but remained on the blade, and Andy – who was unfamiliar with Mudshrimps – exclaimed at the burrows that were exposed, some caught in section, others clearly U-shaped. In one of them, a small Mudshrimp wriggled, its antennae waving. The burrows were barely two centimetres deep, and the shrimps seemed small. Further down towards the falling tide there were drifts of empty shells of Cockles and pink Baltic Tellins, and here the Corophium burrows were densely packed and deeper, the Mudshrimps larger, many at their full size of about one centimetre. The spade came free of the mud with a loud gloop-ing, sucking sound, water spurted from the burrow mouths, and Mudshrimps seemed to explode out, then crawl away. They are defined by their long antennae, nearly as long as their bodies. We watched a shrimp burrowing, and it appeared to sink into the sediment, so rapid was its activity. Here the shrimps had burrowed deeper, some of their tubes reaching down five centimetres, and there were fine burrows containing slim brown polychaete worms, the Ragworm Hediste, too.

The mud on the spade was pale, and below 15 centimetres or so was interwoven with orange-brown fibres, possibly the decomposing roots of former plants. Andy collected some of the mud in my kitchen sieve, and swirled it in a shallow pool before tipping the captured objects into the white enamel pie-dish. Mudshrimps swam about, testing the meniscus and the bottom of the dish with their long, sensitive antennae. We watched them, entranced; they seemed so small and delicate – and yet they can burrow, so very quickly.

Further out on the mudflat were scattered islets, new “lumps of merse” as Adam called them, now stabilised by thin patches of grass; he had watched how the merse had grown outwards in just two seasons. Now, at a low Spring tide, the estuary’s width was obvious and Adam explained how the river channel had shifted over to the western side, leaving great sloping mudflats here on the East. But deep crevasses were carved through the central whale-back of mud, as though the river was trying to break back through again to nibble at the newly-accreted merse. At Campfield Marsh on the southern side of the Firth I had seen metre-high towers at the seaward side of the marsh, capped with vegetation but with steep bare sides. Some of the towers and hummocks had collapsed and were being smoothed and re-distributed by the sea. Here too at Caerlaverock the tides had picked away at the lower tier, shifting the mat of vegetation and exposing compacted sediment and a sharp ‘cliff-edge’. Columns of merse had been isolated. “We call them merse-bergs,” Adam said. “If you’re out here on a quiet day, sometimes you hear a rumble, a bit like thunder – and then you realise that one of the bergs has collapsed.”

Growth-rings in trees, fish-scales, stromatolites and oyster-shells: they are the sequence of responses of living organisms – plants and bacteria and animals – to diurnal and seasonal changes in their environment. The bodies of the bergs and towers of the saltmarsh are not alive, but where they have been sliced open by the tides their inner structure is exposed, striated with subtly different colours and textures, bands of jagged white shell fragments and rounded pebbles between the layers of silt, a record of particles that have been swirled into their environment throughout the years. The marshes and merses erode and accrete, the removal and deposition of sediment changing with the weather and the tides, the seasons and the years and on geological timescales.

(1) Norman Nicholson (1949) Cumberland and Westmorland. London, Robert Hale

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