Another Life: Drifting seeds have colonised some of our shores

Michael Viney: Climate warming could facilitate exotic newcomers on western coasts

The sea pea is a nomad, seeking to raise its beautiful blue-purple flowers on ocean strandlines around the temperate zone. Illustration: Michael Viney

The sea pea is a nomad, seeking to raise its beautiful blue-purple flowers on ocean strandlines around the temperate zone. Illustration: Michael Viney

 

It’s some 30 years since Dan Minchin, a marine biologist, took me for a trudge along a winter shore in south Connemara. As a veteran beachcomber, he was my mentor along the tideline.

I wanted to know, for a start, about these small plastic cylinders I’d been finding, about the size of a cigar. Minchin had one handy and twisted it sharply, whereupon it glowed brightly on a dull day. It was a chemical light-stick, used in long-line, deep sea fishery on the other side of the Atlantic.

There was more plastic among the seaweed at the furthest reach of the tide – a confetti of tiny pellets in assorted colours. Today they’re called “nurdles”, the form in which raw plastic is shipped around the world. Their menacing pollution, some of it gaseous, was even reported to Cop26.

Minchin, however, was scanning between the nurdles to gather some amber, pea-like seeds. Along with his mainstream studies of aquatic invaders to Ireland – alien seaweeds, Asian clams and crabs and more – has come a personal obsession with a vagrant plant whose drifting seeds have colonised some of our shores.

Exposed shores

The sea pea, Lathyrus japonicus, is a nomad, seeking to raise its beautiful blue-purple flowers on ocean strandlines around the temperate zone. It has populations on exposed shores from Newfoundland to New Jersey and from Norway to the Baltic. In Ireland some may survive for decades, then disappear after sand-eroding storms, making it a rare plant.

Irish records go back centuries – in Dingle Bay, to 1756. Minchin’s latest paper reports on Ireland’s only known flowering population, expanding along an estuary in Co Cork. He revisited it a dozen times over almost 30 years to count its plants, increasing from a small group of 16 to several thousands. By 2020 it needed a drone to map them.

Over the same years he had searched, often with his daughter, along 148 separate shores, some of them 10 times and more. From strands in Co Donegal to Co Waterford, he collected more than 500 seeds.

Along with them, he gathered North American fishery tags. A single beach on Achill Island yielded 68 in one year, most of them from the Canadian lobster fishery. Hard proof of the seeds’ transatlantic origin would need genetic analysis, but Minchin finds it at least “plausible”.

That’s a bit cautious compared with the judgment of botanist Charles Nelson, writing on Irish drift seeds in 2000: “While I cannot prove that the sea peas found in such large numbers in Ireland and Cornwall all come from North America, I am convinced that this is the least improbable improbability.”

Horse-eyed bean, Mary’s bean, sea purse and nickar nut are others that bob along the same way, taking perhaps 400 days to make the journey

Nelson, based for many active years at the National Botanic Gardens at Glasnevin, wrote what has become a bible for Irish beachcombers patrolling stormy strands for drift seeds. Sea Beans and Nickar Nuts, his authoritative handbook for the Botanical Society of Britain and Ireland, is now listed online by Summerfield Books.

On its cover, crowded with the fascinating variety of transatlantic drift seeds, the big one is Entada gigas, the “sea heart”, up to 6cm across and with a tough, dark skin that invites fondling, taking on a polish like Moroccan leather.

Falling from a metre-long pod of a rampant liana in tropical America, it arrives here by way of the Gulf Stream and North Atlantic Drift. Horse-eyed bean, Mary’s bean, sea purse and nickar nut are others that bob along the same way, taking perhaps 400 days to make the journey.

I have a goodly platter of beans, mostly of the sea heart variety but topped by the grapefruit-sized husk of my one prize offering: the box nut Barringtonia asiatica, retrieved from a beach on the Inishkea Islands and the first found on a European shore.

Sumptuous trays

As my beachcombing years tapered off, sea hearts seemed to be getting scarce and I speculated on the destructive pace of Caribbean mansions and golf courses. From the US, however, online Beachcombing Magazine offers sumptuous trays of a collection currently amassed from a southern Texan island. Such beans!

Spurred on by the resilience of the sea pea, beachcombers weigh the chances of getting other drift seeds to grow.

Given a rub with sandpaper, Lathyrus may indeed flourish in well-drained patio pots, but anything tropical will need a constant 25 degrees, high humidity and a very lofty livingroom. In experiments at Glasnevin, sea purse and horse-eye beans both topped 1.5 metres within 17 weeks.

If they could survive the frosts of Irish winters, wrote Nelson, “our western coasts would be festooned with vines of monkey-ladders, horse-eye beans and Mary’s beans and thick with prickly shrubs of nickar nuts”.

The way climate is going, their needs may indeed be met by the end of the century.

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